Washington State University Extension

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GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written October 25, 2015

I occasionally get asked to give a presentation on “putting the yard and garden to bed for the winter.” Fall garden chores are pretty simple and can be designated as “should-do” and “good-to-do”. I am not sure I could give a thirty minute or longer presentation, but here are the “should-do’s” for fall.

RAKE LEAVES: On the should-should do list is raking leaves. If you have a number of trees like I do, the leaves can certainly pile up. They tend to blow around and pile up at my back door and elsewhere in the landscape. As we start to get more dew and moisture, these leaves can mat down and smother the grass and other plants. Get those leaves raked up and consider using them for making compost or tilling them into your vegetable garden soil where they will decompose over the winter and help improve the soil.

MOW THE GRASS: After the stress of a very hot summer, your lawn needs all the help it can get. You should keep mowing if the lawn is growing. Do not mow the grass extra short and then put the mower away. Also, do not leave it extra long, as this can lead to matted grass and favorable conditions for snow mold. (This past spring snow mold fungus showed up in many area lawns and caused significant damage.) Mow at the recommended height of about 2.5 inches until you no longer need to mow. The good news is that as the weather cools, you will not need to mow as often.

TREAT FOR BROADLEAF WEEDS: If broadleaf weeds, like dandelions or clover, have shown up all over your lawn, now is the time you should treat for these weeds with an herbicide spray. However, if you only have a few of these weeds here and there, dig them out by hand or pop them out with a “weed popper.”

Herbicide sprays for broadleaf weeds will not control grassy weeds. Annual grasses, such as crabgrass will die with a hard frost, and need to be controlled next spring with pre-emergent herbicides or “preventers” that will keep the seed from germinating and growing. Perennial grasses, such as Bermuda grass, are not controlled with fall chemical applications.

DIG TENDER BULBS: Many of the tender bulbs, corms, rhizomes, and tubers that we plant in our gardens, including cannas, calla lilies, gladiolas, and dahlias, are tropical plants from warmer climates (Zones 7 to10) where they can stay in the ground over the winter. In cooler climates (Zones 6 and lower) like ours, they should be dug each fall and stored for the winter in a cool, dry protected location where they will not freeze. Some years in our area these tubers and bulbs may survive if left in the ground and heavily mulched. However, if winter brings severely cold temperatures, they will be killed.

To store them, wait about two weeks after frost kills their tops and then carefully lift the tubers, rhizomes or corms from the soil; shake off as much of the soil as possible; rinse them with clean water; and let them dry in a protected dry spot. Place them in cardboard boxes or paper bags using dry sawdust, wood shavings, or peat moss for packing.

You know, maybe I could give a talk on getting your yard and garden ready for winter. There seems to be a lot to do in the fall. More soon on the “good-to-do” fall garden tasks.


GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written September 6, 2015


This summer was tough on many area lawns, especially those where watering was restricted. Owners of ravaged lawns are wondering what to do now.

The first thing to do is assess the damage. Are spots and areas truly dead or did the grass just go dormant? With cooler weather and more water available, dormant grass should be starting to show signs of life. Check the brown areas closely looking for new grass blades. Once water becomes available, grass that is dormant greens back up within two weeks.

If no green growth is apparent and patches are a crispy yellow-brown or a grayish color, it is likely the grass is completely dead. Fall is a good time to re-seed or re-sod those areas, as long as irrigation water is available.

Because it takes some types of grass seed, like that of Kentucky bluegrass, up to two weeks to germinate, seeding must be done early enough to allow time for the seed to germinate and grow mature enough before hard frosts occur and before irrigation water is turned off. The average date of the first hard frost in this area is October 15th (note this is only an average date), so lawns must be seeded in early September. Re-sodding can be done later in the fall, as long as water is available and the soil is not frozen.

Water is critical to the success of both re-seeding and re-sodding. The soil must be kept moist to enable germination and provide moisture for root growth. If water is not available, you will be wasting time and money.

If more than 50 percent of your lawn is dead, you will probably want to consider complete renovation. You must get rid of the dead grass and any thatch before you can re-seed or re-sod. Seed and sod roots must be in touch with bare soil. Do this by mowing as low as possible and then using a rake, dethatching machine, or sod cutter to remove grass and thatch. Once you have bare soil, apply a starter fertilizer and the seed at the recommended rates on the labels and then rake the seed into the top of the soil.

If “only” 25 to 50 per cent of your lawn is dead, complete renovation can be avoided with over-seeding. First mow the lawn at a height of one and a half inches. Then you will need to rent a machine called a slit seeder or find a lawn care company who can come in and do this for you. The slit seeder cuts down through the grass and thatch and into the soil, dropping grass seed into the slit it creates. If you do this yourself, make two passes over the area in opposite directions. Check to make sure the seed is ending up planted at least 1/4 deep in the soil. Finish up with an application of lawn starter fertilizer and a light raking.

Next, moisture is needed to promote the germination and growth of the seedlings. This can be tricky as you need to water frequently enough to keep the soil moist but not too wet. Excess moisture can lead to disease problems. Once the grass germinates and plants develop several leaves, you should water more deeply and less frequently.

For lawns that survived the heat and are still green and growing, fall is the best time to fertilize. Apply fall lawn fertilizer in early September and again in early November.


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published- MAY 9, 2014


I grow all my annual flowers in big pots on my back patio. At last count, there were ten of them and replacing the potting mix in them every year would bankrupt me. Instead of buying new potting mix each spring, I “refresh” and reuse the old.

I start by digging out all the dead roots and stems of last year’s plants, if I didn’t remove them in the fall. Potting mixes tends to compact over the course of the growing season, so next I use a trowel and garden knife to break apart residual roots and loosen the mix to a depth of at least eight inches. Along with loosening the mix each spring, I also add some controlled-release fertilizer and work it into those top eight inches.

After refreshing the mix, I add some new potting mix if the level in the pot has declined due to decomposition or from removing the old plant roots intermingled with mix. After several years, I may replace the old mix in the top half of the pot with new because it is not draining well due to the break down of organic matter over time. When I remove old mix, I don’t throw it away. Instead, I mix it into my sandy garden soil.

I recommend investing in a quality potting mix when starting a new container. I prefer a mix that consists of peat moss or coconut coir, perlite or pumice, earthworm castings, and some compost. I also like the ones that contain controlled-release fertilizer that the label indicates will last for several months.

I mentioned earlier adding fertilizer to potting mix that is being reused. This is necessary because last year’s plants probably used up most of the available nutrients and whatever they did not use was likely lost through leaching with the frequent watering necessitated by hot weather. The addition of fertilizer to reused potting mix is important for the good growth of the annuals, flower or vegetables, planted in containers. Just imagine the fertilizer needs of a vigorous growing sweet potato vine, trailing petunia, or tomato vine!

I prefer controlled-release or “time-release” fertilizers for use in my containers. They are more expensive than traditional water soluble granular fertilizers, but I like the convenience of not needing to reapply them frequently during the season. When I select a controlled-release fertilizer, I look for one that is a balanced fertilizer, one that contains nitrogen (N), phosphorus (P), and potassium (K). The percentage of these by total weight is indicated somewhere on the product label in that order: N, P, and K. Because the amount of nutrients vary with different types and brands of fertilizer, I follow the recommendation on the label for the amount to apply to a particular size pot.

Product labels also indicate the length of time that the nutrients should last. However, because hot summer and early fall weather in our region dictates frequent watering, it may not last that long. You should consider applying the same fertilizer again in mid-summer. If not, you can use a water soluble liquid or crystallized fertilizer to add some nutrients later in the season if the plants are showing signs of nutrient deficiency, such as yellowing leaves or poor growth.

Anxious to get started, I readied by containers over a month ago. Now I am anxiously waiting for consistently warm and calmer weather before I get started. Maybe this weekend? We’ll see.

Published: 5/9/2014 11:43 AM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published 9/6/13

As the garden season winds down, many gardeners may be thinking it is time to relax. It is not. Now is the time to make a checklist of fall gardening chores that should be done before fall’s end.

First on the list should be fertilizing the lawn. Early September and late October are the two most important times of year to fertilize your lawn. During the hot part of summer cool season grasses become stressed. Grass shoot and root growth slows to a stop. As the weather cools in fall, the grass begins to grow well again, establishing new roots and putting on sideways growth that increases lawn thickness. Nitrogen applied in the fall helps the grass recover from the stresses of summer.

Fertilizer applied now helps stimulate shoot growth. A late fall fertilization, applied after the grass stops growing, promotes root growth and the storage of food reserves needed for spring growth. This late fall application also keeps the grass looking greener through the winter and you should not need to fertilize again until April or May.

WSU recommends using a top-quality lawn fertilizer that contains some slow-release or controlled-release nitrogen, such as IBDU, sulfur-coated urea, or urea formaldehyde. These fertilizers release nitrogen over an extended period of time and allow for more even growth during the growing season. Fertilizers with soluble nitrogen, such as ammonium sulfate or urea, with nitrogen in a quickly available form are best for late fall fertilization.

Next on your list should be taking care of lawn weeds. If you just have a few weeds here and there, take them out with a weed digger. If the problem is more serious, you may want to consider the application of a broadleaf weed killers. October is a good time for applying these materials.

For weeds like black medic, bindweed, mallow, dandelions, plantain, and clover a combination herbicide product containing 2,4 D and MCPP should provide good control. A lawn product containing triclopyr will help with tough-to-control broadleaf weeds, like oxalis, prostrate spurge, henbit, ground ivy, and lawn violets. As with any pesticide product, be sure to read and follow label directions.

Now is also a good time to order or purchase spring flower bulbs for planting next month after the weather cools. Keep in mind that bigger (more expensive) bulbs produce bigger flowers. If your bulbs are packaged in a plastic or closed paper bag take them out and place them in an open well ventilated tray located in a cool (50 to 60 degrees Fahrenheit) spot.

Wait to plant the bulbs until the soil temperature drops below 60 degrees Fahrenheit. This temperature allows for root growth without stimulating leaf growth. Don’t forget the bulbs need water, so water them in right after planting and whenever needed during mild fall and winter weather to keep the soil slightly moist.

Other tasks to put on your list include:

raking up leaves

building a compost pile

dividing spring and early summer flowering perennials that have become crowded

cutting back to the ground the dead tops of perennial flowers

weeding and cleaning away plant refuse in garden and landscape beds

aerating your lawn if the soil is compacted

giving all your trees, shrubs and perennials a good deep watering before the water is shut off for the season


Whew! That’s a lot of work. You and I should get busy.



Published: 9/6/2013 2:28 PM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
Published 4/6/2013

It’s very hard to wait to fertilize your grass in the spring when everything else in the yard is turning green, but you should wait. ‘Greening’ your lawn up early in the spring may make you feel good, but it’s not recommended.

Wisdom regarding why you should wait to fertilize until later in spring comes from Dr. Peter Landschoot, the extension turfgrass management specialist at Penn State University. He points out that while marketers may call fertilizer ‘plant food’ the real food that fuels turfgrass are the carbohydrates that grass makes via photosynthesis. Like all green plants, grass uses light energy to convert water and carbon dioxide into carbohydrates.

While fertilizers are nutrients required for plant growth, carbohydrates provide the fuel for growth. Landschoot points out that these self-manufactured carbohydrates are stored in the stem and crown of the grass plant when more are made than are being used. Similar to many other perennial plants, the carbohydrates are stored in the greatest amounts in the fall as plant growth slows. These extra carbohydrates are kept in reserve to help the grass recover when stressed or injured in the coming growing season.

Carbohydrates are used up at a high rate in the spring ‘especially under low mowing heights and high nitrogen fertility,’ says Landscoot. That’s why you should not apply nitrogen fertilizer in early spring or mow below the optimum mowing height. (WSU recommends a mowing height of 1.25 to 2 inches for Kentucky bluegrass lawns.) Turf experts at Cornell University also point out that fertilizing healthy lawns in early spring ‘increases top growth (and mowing chores) at the expense of root growth. ‘

WSU recommends fertilizing your lawn no earlier than May 1 in eastern Washington unless nitrogen deficiency is apparent. Exceptions to the May 1 date are lawns that weren’t fertilized the previous fall or lawns that have sustained winter injury. However, fertilizer should not be applied until the soil temperature has warmed to 55 degrees Fahrenheit.

It is important to note that the very best time of year to fertilize your lawn is early November (November 1–15) when the soil is cooler and the grass plants are recovering from summer heat and growing new roots and tillers.

How much fertilizer should be applied? Kentucky bluegrass, the predominant grass in most local lawns, should receive 2 to 4 pounds of nitrogen per 1000 square feet of lawn. Use the two pound rate, if you have an older lawn or if you are returning your clippings to the lawn with a mulching mower. The four pound rate is recommended for young lawns, lawns on sandy soils, or lawns where the clippings are being removed. Apply only one pound of nitrogen per 1000 square feet per application. The optimal times for applications of nitrogen, in addition to the November and May dates, are mid-June (June 15) and early September (September 1).

As much as you and I want to see that green grass growing in our yards, our wisdom and patience will be rewarded with a healthier, denser lawn that can better resist drought stress, weed invasions, and attack by diseases.

Published: 4/6/2013 11:11 AM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA

Eager first-time gardeners may be so anxious to start their garden that they fail to take the time to adequately prepare the soil. The key to garden success starts with the soil. If you have bad soil, your success will be limited.

So what’s considered a ‘bad’ soil? Soils that are compacted, or don’t drain well, or drain too well and don’t retain moisture, or don’t contain nutrients are bad soils that need help to become productive.

Organic matter is the magic potion for creating a better soil from bad soil. Organic matter (OM) improves the drainage of compacted or heavy soils by increasing the porosity. It helps sandy soils retain water and nutrients. OM also acts as a slow-release fertilizer over time, releasing nitrogen, phosphorus, and sulfur.

However, OM can turn into ‘bad magic’ if you add too much. Don’t overload the soil by applying more than one to two inches of organic matter before tilling it into the soil. Fall is a good time to add uncomposted OM to your soil, especially when starting a new garden.

The wrong types of OM will can also spell trouble. The microbes in the soil responsible for breaking down organic matter need nitrogen to reproduce. Materials with a high carbon to nitrogen (C:N) ratio will tie up all the available nitrogen. The garden plants will suffer because they can’t get enough nitrogen from the soil for healthy growth. That’s why it’s best not to use straw, straw bedding, sawdust, wood chips, or bark as the source of organic matter because they all have a very high C:N ratio.

Organic matter with a low C:N ration, such as fresh manure and grass clippings, are a good source of nitrogen, but usually aren’t as good in building the soil. Materials with a moderate C:N ratio, such as chopped tree leaves, compost, and cover crops, don’t provide as much nitrogen to plants, but do a better job of adding OM to the soil.

More Bad Magic: When adding manure from a feed lot or dairy barn, be aware that these materials may be high in accumulated salts because of animal urine. Fall is a good time to on to apply manure so winter precipitation can leach salts away.

Health Alert!… More Bad Magic: When adding manures to your vegetable garden, you risk exposing you and your family to E. coli bacteria and other pathogens in the manure. To reduce the risk, WSU recommends against using fresh manures on your garden. If you do use fresh manure on the garden, they recommend waiting 120 days after application before harvesting high risk crops and 90 days before picking harvesting for low risk crops.

High risk crops are those in direct contact with the soil and that are often eaten raw. This includes leafy greens, such as lettuce and spinach; as root vegetables, such as carrots and radishes; and vining crops left to sprawl on the ground, such as melons or cucumbers. Low risk crops are those that don’t touch the ground or that are typically cooked before eating, such as sweet corn, squash, and eggplants.

To minimize the risk it would be best to apply fresh manure to the garden in the fall of the year or use professionally composted manure from a commercial facility where hot composting was practiced.

Keep in mind that organic matter can be the magic potion that transforms a bad soil into a good, but be sure to apply the right kinds of OM, don’t add too much, and be careful when using manures.

UPCOMING CLASS: Marianne Ophardt, WSU Extension Regional Horticulture Specialist, will be teaching a Backyard Composting Workshop on Saturday, April 28 from 9:30 a.m. to noon inside the Highland Grange Hall, 1500 S. Union Street. Participants registering for this free program will receive a free composting bin and book for attending. Seating is limited. For more information or to register, call 735‑3551.

Published: 4/6/2012 9:38 AM


written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA

Whether your lawn is pampered or neglected, weed free or overcome with weeds, fall is the most important time of the year to give it the attention it deserves.

Summer heat stresses the cool season turf grasses in our lawns. As the weather cools in early fall, lawns start to recover. You can help that recovery along with properly timed fertilizer applications. An early September (Labor Day) plus a late October (Halloween) or early November application are recommended for our region.

You still need to irrigate your lawn, but as the weather cools you should be cutting back on the amount of water being applied. If you’re watering everyday, you may only need to water every second or third day. By watering everyday when the lawn doesn’t need it you’re wasting water, washing away needed nutrients, and encouraging the growth of weeds.

Weed Management:
One of the best ways to manage lawn weeds is to encourage a healthy turf with properly timed fertilizer applications and irrigation. However, weeds still find their way into lawns and October is the best time to apply herbicides for the control of broadleaf weeds. That’s because many of the perennial broadleaf weeds in our lawns, such as dandelions and plantain, are actively growing during the cool fall weather. Herbicides applied when they’re actively growing are more effective.

There are also winter annual broadleaf weeds, such as chickweed, that germinate in the fall and grow during late fall and early spring. These are more easily controlled in the fall when the plants are young and small. Efforts made in the fall to encourage a dense, healthy turf, can also help control summer annual weeds, such as crabgrass, purslane, and pigweed, that will germinate in the spring. A dense turf makes it more difficult for weeds to germinate and grow.

Also, fall is a good time of year to apply herbicides to your lawn because landscape plants are not actively growing and not as susceptible to damage from the herbicides.

Which Herbicides?:
There are a number of broadleaf weed control products on the market. Most broadleaf lawn weeds can be controlled with a combination of 2,4 D, MCPP, and dicamba. However, products containing dicamba should not be used in the root zone of desirable trees and shrubs because they can cause damage. This includes trees and shrubs growing in the lawn area or along the lawn border. Even if trees and shrubs are in a landscape bed, they’re still vulnerable if their roots are growing into the lawn area. Keep in mind that the absorbing roots of a tree can be located in areas as far from a tree as that tree is tall and beyond! If you have vulnerable plants with roots throughout the lawn, it would be advisable to simply spot treat weeds or use a product that doesn’t contain dicamba.

There are also certain lawn weeds that are particularly difficult to control, including bindweed, black medic (Japanese clover), clover, creeping wood sorrel (oxalis), ground ivy, henbit, mallow, prostrate spurge, violet. Better control of these can be achieved with lawn herbicide products containing triclopyr.

Before purchasing any herbicide product for your lawn, identify the weeds you’re trying to kill. WSU Master Gardeners can help you identify your weeds. Just dig them up and place them separately in zipper-locked plastic bags. Bring them to the Extension office (735-3551) in Kennewick in the Benton County Annex at 5600-E West Canal Dr. Of course, read and follow all label directions and precautions on the herbicide product you select.
Published: 9/3/2011 11:48 AM


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

Now what? You’ve decided where to place your garden and how big it will be, plus you’ve already worked up the soil. The next steps are preparing the soil and fertilizing.

STEP FOUR – PREPARING THE SOIL: Few gardeners are satisfied with their soil. Complaints range from soil that’s too heavy and poorly drained to soil that’s too sandy and dry. The solution for both these problems is the addition of stable organic matter. Good quality compost is one of the easiest ways to add organic matter to your soil. The compost should be dark and crumbly, with no identifiable chunks of bark, twigs, pieces of wood, or other items. You can usually purchase compost in bulk from a local garden center.

How much is needed? You should never add more than one-third by volume of relatively stable organic matter to your soil. That means if you’re working the soil to a depth of six inches, don’t add more than two inches of organic matter. Peat moss and coconut coir are two other types of stable organic matter that are readily available to gardeners, but both are considerably more expensive than compost. Some gardeners don’t like to use peat because there are environmental concerns about harvesting it from bog ecosystems in Canada. However, the Canadian peat industry is well regulated and harvesting is balanced with restoration practices to protect this natural resource.

If you have concerns about using peat moss, look for coconut coir. Coconut coir is a renewable byproduct of the coconut processing industry and comes from the coconut husk. It’s sold in dry compressed “bricks.” Look for the fine type, not the coarse, chunky kind, to add to your soil.

To thoroughly mix organic matter into the soil, use a spading fork. This is hard work. If you find the task too backbreaking, consider renting a rototiller. It will also come in handy for working fertilizer into the soil, which is the next step.

STEP FIVE -FERTILIZING: If you’re starting a garden in a brand new spot and adding organic matter, you’ll also want to add some fertilizer. An excellent organic fertilizer is rabbit manure. This is the perfect manure to till into the soil. It’s easy to transport and not as smelly as most other manures. You may be able to find free bunny poop advertised on-line or in newspaper ads. Start with about 20 to 30 gallons of rabbit manure per 100 square feet of garden area. Other manures will work, but they’re often bulkier and smellier, plus some will contain weed seeds that are still viable even after spending time in an animal’s digestive system.

Another great source of nitrogen and organic matter for the garden is alfalfa pellets. Alfalfa pellets are dried, ground alfalfa pressed into pellet form. Look for them at a farm and garden store. For adding to the garden soil, use only plain pellets without any additives. Spread about two to three pounds of pellets per 100 square feet of garden area and till them into the soil before planting.

I’m a big fan of bunny poop and alfalfa pellets, but there are also plenty of commercial boxed organic or inorganic fertilizers available that will help your garden grow.

Published: 2/6/2010 10:26 AM


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

Q:Last week you indicated the optimum times for fertilizing a lawn, but I want to know what’s the best fertilizer to use. I’ve been using 16-16-16 or 15-15-15 for years. What fertilizer do you recommend?

A: It’s best to have your soil tested to find out the levels of the these three major nutrients, nitrogen (N), phosphorus (P), and potassium (K). That’s the only way to find out what nutrients are actually needed for good grass growth in your lawn. There are two local soil testing labs where you can take your soil to be tested. Your lawn may only need nitrogen or it may need a complete fertilizer with nitrogen, phosphorus and potassium (N:P:K).

Without a soil test to tell you exactly what’s needed, look for a fertilizer that applies nutrients in the ratio that the lawn uses them. Fertilizers with an approximate ratio of 3:1:2 (N:P:K) are considered “best” for lawns. Because of our dry climate and hot summer temperatures, we tend to water our lawns frequently. This leaches the soluble nitrogen in fertilizers out of the grass root zone, especially on the sandy soils found in some areas. The best turf fertilizers have at least 30 to 50 per cent of the nitrogen in a slow-release form. Part of the nitrogen is rapidly available to the grass and the other portion is released over time. This provides for more even grass growth and keeps you from washing the nitrogen away before the grass is able to utilize it.

Q: Do I need to aerate my lawn to control thatch? Aeration with a hollow-tined aerifier that pulls out plugs of grass and soil from the lawn will help reduce soil compaction. Aeration does not adequately control a serious thatch problem. However, aeration can be used as a stop-gap measure to alleviate the problems caused by thatch. Excessive thatch can prevent the air, water, and fertilizers from getting to the grass roots. Aeration aids in penetration of these elements, but does not remove a significant amount of thatch. Thick thatch should be removed with a dethatching or power-rake machine in early spring as soon as the frost is out of the ground or in late August.

Q: My neighbor dethatched his lawn and it was a big job. What causes thatch and how can I avoid it?

A: Thatch is a partially decomposed layer of mostly grass stems and roots that develops between the top of the grass plant and the soil. It’s not caused by grass clippings. Believe it or not, one of the biggest factors leading to a buildup of thatch is the height at which you mow your lawn. Grass should be mowed at the recommended height for the type of grass. Both Kenucky bluegrass and turf-type perennial rye grass lawns should be mowed at a height of 1.5 to 2.5 inches.

Overwatering also contributes to thatch. Saturated soils lead to surface rooting because that’s the only place grass roots can get air. The remedy is to water deeply, less frequently. You can also encourage thatch breakdown by fertilizing your lawn at the recommended rates and timing. Nitrogen is needed by the bacterial organisms that are part of the decomposition process.

GARDEN REMINDER: Join the WSU Master Gardeners at the Demonstration Garden today from 9:00 to 1:00 for gardening classes and a plant sale.

Published: 4/25/2009 2:49 PM


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

If you go to the garden store, you’ll find a confusing array of fertilizers. It used to be so simple, you just picked up a bag of 16-16-16 or 10-10-10. Now there are a number of specialized fertilizer products, usually much more expensive than the old familiar ones. What’s the difference and are these new fertilizers worth the extra money?

The main difference is in the form of nitrogen they contain. Many of the newer fertilizers contain nitrogen in a slow-release form. They do this by treating the fertilizer so the nitrogen and other nutrients are released more slowly into the soil. This provides plants with nitrogen over a longer period of time and allows for more even plant growth. It also decreases the potential of burning the plants with fertilizers salts. An added advantage is that the fertilizer doesn’t have to be applied as often. Because the nitrogen is in essence spoon-fed to plants, there’s also less chance of leaching and polluting our groundwater with excess nitrogen. This is of great concern, especially in areas with high rainfall… but it’s also a problem in more arid regions like ours where irrigation water can carry excess nitrogen into the groundwater supply.

The primary disadvantage of many of the slow-release fertilizers is the cost. You pay a lot more per pound of nitrogen for these fertilizers than those with quick-release nitrogen, as much as ten to fifteen times more money. Another disadvantage is that you’re not quite sure when the slow-release fertilizer is done releasing. While the manufacturer may intend for a specific fertilizer to last 3, 4, 6 or more months, there’s no easy way of telling just how long it lasts. In many cases, the release of nutrients depends on the soil moisture and the soil temperature. Excessive moisture or excessive heat can speed up the release process.

One other disadvantage of slow-release fertilizers is a characteristic that also makes them desirable …. the nitrogen they contain is not quickly available. Sometimes you have plants that are badly in need of nitrogen, especially early in the growing season. Slow-release fertilizers can be too slow to meet the immediate needs of these plants. To get around this problem, many of the newer fertilizer products also contain some form of quickly available nitrogen. These are called “blended” fertilizers. To get the most for your money, check the label to see how much of the nitrogen is quick-release and how much is slow-release. If you’re wanting a slow-release fertilizer and are paying extra money to obtain it, at least 50 per cent of the nitrogen should probably be in a slow-release form.

There are different approaches to creating a slow-release fertilizer. A variety of innovative technologies are employed. Generally, the newer the technology, the more expensive the fertilizer. Here are a few of the different types of slow-release fertilizers commonly available today.

Pelleted Fertilizer – consists of relatively insoluble forms of nutrients in a “pellet” or “spike”

form. The larger the pellet size, the slower the fertilizer is released.

Chemically Altered Fertilizer: In some cases a fertilizer has gone through a chemical process that makes part of the nitrogen insoluble in water. For some chemically altered fertilizers, the release of nitrogen is dependent on soil microbial activity. The greater the activity of the microbes, the faster the nitrogen is released. Soil microbe activity depends on soil temperature, pH, and aeration. Their activity increases with temperature and decreases with extremes of pH or poor aeration. One example of this type of chemically treated slow-release fertilizer is ureaformaldehyde (also known as UF or Ureaform) with 38 per cent nitrogen ,of which 70 per cent is water insoluble.

Another chemically treated slow-release fertilizer is isobutylidene diurea, known more commonly as IBDU. It contains 32 per cent nitrogen, of which is 90 per cent insoluble. Unlike the Ureaform, IBDU is not dependent on microbes for the release of the nitrogen into the soil. It’s nitrogen is released by chemical hydrolysis. Therefore, the release of nitrogen is more dependent on particle size, the amount of water, and the pH of the water and soil. Many of the IBDU fertilizers are manufactured to last about 5 to 6 months, but they can be coated with plastic for release over a longer period of time.

Coated Fertilizer: As just noted, one way to slow the release of fertilizer into the soil is by coating fertilizer particles with a synthetic coating or with sulfur. Sulfur-coated urea (SCU) is one type of coated fertilizer. SCU is created by coating hot urea fertilizer with molten sulfur and then sealing it with a polyethylene oil, microcrystalline wax, or polymer outer coating. The release of the fertilizer occurs through pores in the coating. How fast it’s released, depends on the thickness of the coating used and the soil temperature.

The most recent technology in garden fertilizers are plastic coated fertilizers, such as Osmocote, Polyon, Nutricote, and ProKote. Coating materials include resin, polyurethane, and polyolefin. These coatings create a semi-permeable membrane around fertilizer particles. The membrane allows water to diffuse inside and dissolve the enclosed fertilizer. The rate of nutrient release depends on the amount of water, soil temperature, and the thickness of the coating. Generally, the thicker the coating, the slower the release. Technology has allowed manufacturers to create slow-release coated fertilizers that last 12 months or even longer!

Well, now you know more about the newer fertilizers found at the garden store and the reason for the wide disparity in cost. However, gardeners who tend to lean towards the more natural side of gardening will want me to point out that there are natural slow-release fertilizers available too… composted manures. Of course, they come with their own advantages and disadvantages that we’ll talk about some other time.

Published: 6/12/2004 2:23 PM

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