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SOIL FOR RAISED BEDS

written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published- JULY 4, 2014

SOIL FOR RAISED BEDS

Today’s homeowners have smaller yards and less space for vegetable gardening. Many have opted to use raised beds for growing vegetables as a way to maximize space and minimize garden maintenance.

‘Square-foot’ gardening, popular with some gardeners, is a raised bed system for optimizing garden production promoted by Mel Bartholemew. His system includes using a potting mix that he calls Mel’s Mix. It contains compost, peat moss, and coarse vermiculite. It can be very pricey, especially if you are filling a number of beds.

Gardeners wanting to grow in raised beds do not need to invest in an expensive soil or potting mix. They can use their own soil in low-sided raised beds. Set up the beds and then take the native soil in the pathways around the beds and mix it with some good quality compost (no more than 10 per cent by volume) and place it in the beds.

If there is not enough soil to fill the beds, you will need to bring in soil. True topsoil is natural surface soil scraped up and transported to a site. Topsoil in many regions is more desirable than the subsoil (the soil layer beneath the topsoil) because natural processes have created a crumbly soil structure that is conducive to good plant growth. However, digging and transporting topsoil elsewhere generally destroys this crumbly structure and nullifies its benefits.

Dr. Craig Cogger, WSU Extension Soil Specialist, recommends sandy landscaping fill as a compromise but notes it will not hold much water and will dry out quickly. (True topsoil in our region generally lacks the crumbly structure found in areas with more rainfall.)

Sandy landscaping fill is sandy soil mixed with organic matter (OM). Probably much of what is sold commercially as topsoil in our region is basically sandy landscaping fill. If you decide to purchase sandy landscaping fill or ‘topsoil’ for your raised beds, ask where the soil came from and what it contains.

Buy your soil or fill from a reputable company. Not all soils sold as ‘topsoil’ should be used in raised bed gardens. They can contain broken glass, too many rocks, wood waste, and other debris. Inspect the topsoil before your buy it and before you accept delivery. You also do not want soil that may have come from an area that was treated with long-term residual herbicides or other chemicals.

Ask if the company has had the topsoil tested or knows how much OM it contains. If the topsoil or landscape fill already contains 10 per cent or more OM by volume (5 per cent by weight), you do not need to add compost or other OM. Dr. Linda Chalker-Scott, WSU Extension Horticulturist, indicates that 10 per cent OM is adequate from a fertility perspective. Adding substantially more OM to the soil contributes to high nutrient levels that can lead to plant health problems. Chalker-Scott recommends before adding organic amendments to the soil in your beds, have it tested to determine the OM content and nutrient levels.

Finally if the soil in your beds is distinctly different from the native soil beneath, it can impede drainage. Cogger recommends mixing the introduced soil with your native soil as you build the bed to create a textural gradient that will allow for better drainage. For more on raised beds consult WSU Extension Fact Sheet FS075E at http://cru.cahe.wsu.edu/CEPublications/FS075E/FS075E.pdf

Published: 7/4/2014 11:40 AM

BUILDING THE SOIL IN YOUR RAISED BEDS

written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
Published 1/25/2013

Back in early December I talked about the first steps of raised bed gardening and promised to talk about ‘building’ the bed or developing the soil in which the plants will grow.

Some proponents of raised beds insist that success is only possible if you fill the beds with a soil-less mix of peat moss, vermiculite, and compost. This mix can be prohibitively expensive and discouraging for a gardener on a tight budget. It also provides a limited volume of soil in which plant roots can grow making it much like growing your garden in a pot.

So what’s an alternative to the soil-less mix for raised beds? Why not use the soil that’s already there? Unless you’re placing your raised bed on a paved surface, you can try to use the soil already present. Start ‘working up’ the soil by digging down 12 inches or more (if possible) and turning over the soil in the bed. (If the soil is dry, water it the day before to moisten the soil.)

Deep digging for some will be impossible because of rocky soil or a thick layer of caliche. In these situations, the use of a soil-less mix or locally available clean topsoil are options. Note that the ‘topsoil’ sold at many nurseries is not true topsoil scraped off the surface of the ground. It’s typically simply a mix of sand and compost.

This faux topsoil should work well in raised beds because it has large pores (spaces between soil particles) which provide good water drainage. Also, it already contains organic matter that helps retain moisture and nutrients. It should be noted that the soil-less mixes and the faux topsoil are likely to dry out more quickly than most native soils because of the large pores. This is an advantage in some areas of the state, but creates a challenge in our region because of our very hot, dry summer growing conditions.

Digging may be arduous, but most area gardeners will find that they can use their regular soil even if it’s a little rocky. When building more than one raised bed, many gardeners take some of the soil between the beds to add to the soil in the raised beds. However, this is usually not enough to completely fill the raised bed. Added faux topsoil will be needed.

Whether using a soil-less mix or faux topsoil, it’s important that you don’t create an interface of two distinctly different textures of soil. This results in poor water drainage. To avoid this, add a three to four inch layer of faux topsoil and mix it together with the native soil by digging and turning the soil. Add another layer of material and mix again, repeating until you have reached the top of your structure. When finished you should have a soil that is at least 12 to 18 inches deep that gradually transitions to the native soil beneath the bed.

Next, how much fertilizer is needed? The only way you can tell for sure is to get your soil tested at a local lab. Once you have a soil test done you’ll know how much nitrogen, phosphorus, and potassium is needed. Then you can decide whether to use organic fertilizer or synthetic fertilizer. As you may already know, my personal fertilizer preference is rabbit manure. For more detailed information on raised bed gardens go the WSU publication on ‘Raised Beds’ at http://cru.cahe.wsu.edu/CEPublications/FS075E/FS075E.pdf

Sidebar: How to Start a School or Community Garden Workshop: WSU Extension and the WSU Master Gardeners are sponsoring this special workshop for anyone interested in starting a successful community or school garden. The workshop will be on February 13th from 4:00 to 6:30 p.m. at the Kennewick Senior Center, 500 S. Auburn Street in Kennewick. Pat Munts, from the WSU Extension Small Farm Teams, will share her insight and experiences working with a number of successful community gardens in Spokane. WSU Master Gardeners will also be available to discuss and answer questions on creating raised beds, preparing the soil, and planting vegetables. There is no charge for the workshop. For more information call 531-5913 or email wtdixon3@gmail.com.

Published: 1/25/2013 10:16 AM

LUMBER FOR MAKING RAISED BEDS

written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
Published 12/14/2012

If you’re building raised beds in your garden or some other type of garden structure, one of your major decisions is what type of wood to use.

Over 20 years ago, gardeners used recycled railroad ties treated with creosote for edging or terracing their landscapes. If railroad ties weren’t available, they would use wood treated with pentachlorophenol (PCP). Significant concerns arose over the human health and environmental hazards that both of these chemicals posed. Both were found to be a risk and the Environmental Protection Agency (EPA) ruled that there are ‘no approved uses of creosote to treat wood for residential use’ and that PCP treated lumber should not be used in home landscape construction.

After the loss of creosote and PCP, a new preservative was developed for outdoor lumber. By the 1970s the lumber industry was offering lumber pressure treated with chromated copper arsenate (CCA).

Unfortunately, health concerns also surfaced regarding the use of this lumber in landscapes and gardens, including play equipment, compost bins, and raised beds. It was found that over time arsenic and chromium leach from the CCA treated wood into the surrounding soil. Both of these heavy metals can be absorbed by vegetables and accumulate in plant tissues. With these concerns, the lumber industry voluntarily phased out the use of CCA lumber and since 2004 the EPA has not permitted any residential uses of CCA lumber.

It’s all pretty scary. So what type of materials should a gardener use to build raised beds? There are still several adequate choices. Wood naturally resistant to wood rot is an acceptable choice. However, resistant to wood rot only means that it will decay more slowly than other types of wood and will need to be replaced at some point. Some naturally rot resistant lumber includes cedar, redwood, juniper, white oak, locust, and Douglas fir.

Another alternative is to use the newest types of pressure treated lumber that utilize alkaline copper quaternary compounds (ACQ) and copper azoles. This type of copper treated lumber is currently considered safe for use in raised beds and other garden structures.

Yet another option is plastic lumber, which is typically the most expensive of all the alternatives. There are three main types:
– Composite plastic lumber generally contains about 50% wood fiber and 50% plastic. It’s not as strong or as stiff as natural wood lumber. Plus, composite lumber is susceptible to stains and attack by molds and mildew. It also discolors and degrades with time. It generally requires more maintenance than 100% plastic lumber.

– Plain plastic lumber contains 95% to 100% Single Polymer/High Density Polyethylene (HDPE) and is made from recycled plastics. It isn’t susceptible to rot or staining, but it’s also not as stiff as wood and also can swell and deform in hot weather.

– Some plastic lumber is made with HDPE (from recycled plastic) that’s mixed with mineral additives to make it stiffer and stronger and to decrease the expansion and contraction that’s a problem with other types of plastic lumber.

You can also use other materials to build raised beds such as concrete blocks, bricks, and stones. A less expensive option is the use of various recycled materials, such as recycled sidewalk concrete used as blocks.

If you chose any type of lumber for your beds, the next step is construction. We’ll talk more about that soon.
Published: 12/14/2012 2:30 PM

STARTING A RAISED BED GARDEN

written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
Published 12/07/2012

Raised-bed gardening has become very popular in our region and across the nation. For some, raised beds are probably just a trendy gardening fad, but there are some very sound reasons their use has been burgeoning.

The size of new home landscapes is generally decreasing, providing limited space for vegetable gardening activities. Because raised beds can be built in limited space areas, they’re often preferable to larger vegetable garden plots. Plus, raised beds encourage more intensive gardening, yielding greater production from each square foot of garden space.

Raised beds can also make gardening less arduous and more successful in areas where the soil is extensively rocky, poorly drained, extremely compacted or very shallow. In areas with poor soils, it’s easier and less costly to add organic matter and other soil amendments to the limited soil volume contained by the raised beds rather than to a larger garden plot.

Another big reason that gardeners like raised beds is that they’re easier to maintain. The area where weeds and other pests must be controlled is limited. Because of the confined area, it’s also easier to use water-conserving methods of irrigation, such as drip or soaker hoses. While many raised beds are only about six inches in height, they can be taller to allow for those who have trouble bending or to provide access for gardeners in wheelchairs.

With so many legitimate reasons, it’s easy to see why raised beds have become popular. If you plan to venture into the world of raised bed gardening, now is a good time to get started. Use these winter months to plan where you want to have your beds located and their dimensions. Here are some guidelines:

1. Beds should be no more than 4 feet wide for ease of access in reaching plants near the center of the bed. Make them narrower if your reach is limited or you’re only able to access a bed from one side.

2. Beds can be any length you want. Many gardeners like beds that are about 8 feet long, but let your allotted space dictate the length and number of beds to construct. Hint: You may want to start out with only one bed the first year.

3. If constructing more than one raised bed, leave at least two feet between beds to allow access to your beds. Make the aisles wider if you want to be able to use a garden cart or wheelbarrow between the rows.

4. If growing vegetables, be sure to locate the bed where it will receive six hours or more of full sun. If possible, the length of the bed should run north and south to prevent taller plants from shading smaller ones.

If the weather stays mild, you may want to go out and stake your planned bed or beds in the spot you’ve decided upon. This should give you a better idea of how well they fit and if you’re allowing yourself enough room between the beds.

Once you’ve figured out the size and placement of your beds, you can start thinking about construction… what type of materials to use, the needed hardware, and how much material will be needed for construction. After that will be soil preparation.

Did you know you shouldn’t use pressure treated lumber because it releases toxic minerals into the soil? Next time we’ll talk about a which woods and materials are best for construction.
Published: 12/7/2012 2:24 PM

STRAW BALE GARDENING IN THE TRI-CITIES

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

Last year I got very exited about an article I read in the June issue of ‘Fine Gardening’ magazine. It was titled ‘Build a Garden Out of Straw,’ by Amy Stewart. Straw bale gardening is a hot new trend in many areas, but gardeners like Stewart that have successful straw bale gardens are located in areas with much cooler summer climates. I wondered if they would work here in the Tri-Cities.

First, what’s a straw bale garden? A straw bale garden is a ‘conditioned’ bale of straw where plants are growing in the straw bale, instead of in the soil. All sorts of vegetable crops can be grown in the bales, including garden favorites like tomatoes, peppers, squash, and melon.

Why garden with straw bales? Straw bale gardens are inexpensive, they don’t require any digging, they can be placed on a patio or driveway, and they’re temporary. Also, the bales create a raised bed situation, making gardening easier with less bending.

A number of local gardeners have adopted square foot vegetable gardening where intensive methods of growing vegetables are utilized. However, square foot gardening requires building structured permanent beds, dividing the beds into one-square-foot grids, and carefully following a schedule for planting, harvesting, and replanting for successive cropping in each square. It takes an attentive gardener to manage a square foot garden well.

In addition, the recommended soil mix used in the square foot garden beds is prohibitively expensive for many. Oat or wheat straw bales are inexpensive ($3 to $5 a piece) and no building materials are required. The only other expenses include a bag of inexpensive fertilizer, such as 21-0-0 to condition the bales before planting, a complete water soluble fertilizer for fertilizing the growing veggies, and some quality potting mix.

To condition the bales and get them ready for planting, they’re first watered thoroughly and then fertilizer is spread across the top of the bale. This jump starts the decomposition of the straw. After two to three weeks the bales are ready for planting. Transplants or seeds can be used for planting in the straw bale. After planting, regular watering and fertilizer are needed to keep the veggie plants healthy and growing.

The bales only last one season, two at the most. When they no longer have integrity as a bale, the partially rotted straw can be composted or tilled into the soil.

This spring, one of our local Master Gardeners, Eileen Hewitt, decided to give straw bale gardening a try. Her home sits on very hard, rocky ground in Kennewick where just digging a hole is a monumental task and tilling the ground for a garden is a virtual impossibility.

Hewitt found a source of oat straw bales ($3 a piece) and placed several in her back yard. She followed the step-by-step instructions for building a straw bale garden and planted tomatoes, squash and melons in her bales and now she’s happily harvesting fruit from all her ‘straw bale’ plants.

With such hard soil Hewitt doesn’t plan to use the disintegrating bales of hay for tilling into her yard, but gardening friends have already asked her for the straw when she’s done with the bales. Can we successfully grow straw bale gardens in the Tri-Cities? Hewitt answers, ‘Yes!’ and she plans to grow in straw bales again next year.

A handout on ‘Straw Bale Gardening’ is available by calling the Benton County WSU Extension Office at 735-3551 or on-line at http://benton-franklin.wsu.edu/.

Published: 8/27/2011 11:33 AM

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