Washington State University Extension

Garden Tips

Archive for August 2016


GARDEN TIPS – Written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Published August 7, 2016

Kudos to our firefighters for their hard work in fighting the recent wildfires and successfully protecting local homes. Since they do their part in keeping us safe, local home owners should help in the protection of their properties with fire-resistant landscaping. In the short term, there are some easy steps you can take to provide some protection to your home. If your home is situated in an area vulnerable to wildfire, the longer term actions of designing and creating a fire-resistant landscape should be undertaken.

Mulches: Many of you know I favor bark mulches in the landscape because they add organic matter to the soil as they decompose, conserve soil moisture, control weeds, and keep the soil cooler than rock mulches. However, when working to create a fire-resistant landscape, the use of bark or wood chips should be eschewed in favor of non-flammable gravel or rock mulches. Gravel or rock mulches are best especially when mulching any areas that are close to buildings, fences, wood decks, or other wooden structures.

Raised Beds: Raised beds are a big trend in gardening right now, but they are predominantly constructed out of wood. In fire-vulnerable areas, it is better to build raised beds with bricks, concrete blocks, rocks, corrugated metal, or other non-flammable materials.

Landscape Maintenance: While not everyone craves a neat and tidy landscape, yard cleanup and the removal of plant litter is one way to reduce fuel for potential wildfires. So get busy now raking up the layers of dead pine needles and arborvitae foliage beneath these evergreens, dry leaves that have piled up in nooks and crannies around the yard, or bunches of dry plant litter anywhere else. If pines or other needled evergreens are situated close to your house, regularly remove their litter that accumulates on the roof and in gutters.

Keeping potential sources of fuel in mind, be sure to store any firewood 30 to 100 feet away from structures and also keep vegetation away from area. Eliminate any piles of plant litter, such as grass clippings, you may be accumulating. Also, remove dead shrubs and tree branches in your landscape. Cut down weeds and brush in areas of your property that are not landscaped.

Lawns: In regions like ours where the supply of irrigation water is a constant concern, limited areas of lawn are advocated to conserve the amount of water needed to keep grass green during the heat of summer. However, green lawns do resist fire well and efforts should be taken to maintain this green space around your home. However this is not a license to apply water heedlessly. You should still water more deeply, less frequently to save water and promote a healthy green lawn.

Trees: Because I like trees and appreciate the cooling value of their shade, I have ten trees in my yard. If I was in a fire-vulnerable area, I would need to consider pruning off the lower limbs of my trees to remove this ladder fuel. Ladder fuel is plant vegetation, green or dry, that permits fire to ascend into the tops of trees. Pruning off limbs from 6 to 15 feet up is recommended. For the health of the trees, this is best done with proper pruning cuts when the trees are young.

Landscape Design: Creating a well designed “firewise” landscape is very important if your home is situated where it is vulnerable to wildfires, especially if in the wildland-urban interface area. You can help defend your home with sound firewise landscaping. For information on firewise landscape design, go to the University of Idaho’s publication “Protecting and Landscaping Homes in the Wildland/Urban Interface” available at For a list of firewise landscaping plant materials go to:


GARDEN TIPS – Written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Published July 31, 2016

While both new and experienced gardeners know that garden soil may benefit from the addition of compost, they do not know about the problems that can arise when from adding too much or using poor quality compost. Let’s take a little time to chat a bit about the pitfalls of adding compost to garden soil.

While good quality compost is considered the holy grail of garden organic matter, there are no set standards for compost. The quality of compost varies with the types of materials composted and the composting processes used. Mature compost is one where the organic materials are fully broken down into stable organic matter. Quality compost is mature compost that is not high in salts, contains no contaminants from industrial waste, has few weed seeds, and can provide plant nutrients.

You can not discern quality compost by looks. If purchasing commercially made compost, ask the seller for a copy of the laboratory analysis provided by the compost producer. Look for the carbon to nitrogen ratio (C:N) that indicates the stability of the organic matter (OM). A ratio between 12:1 to 15:1 is an indication that the OM is stable. If the ratio is less than 10:1, it is an indication that it contains organic materials that are still in the process of decomposing. A ratio above 25:1 indicates that the compost contains high carbon materials that break down very slowly and will tie-up available nitrogen as it decomposes, depriving garden plants of nitrogen and hampering plant growth.

On the analysis look for the EC or electrical conductivity of the compost. This is a measure of the soluble salts in the soil. High soluble salt levels are harmful to plant roots. Compost with an EC above 8mmho/cm are high in salts and should be avoided. It is better to purchase compost with an EC that is between 0 and 4 mmhos/cm.

Also, pay attention to the percent (by dry weight) of organic matter in the compost. If the percentage is lower than 30 per cent, it means that soil or sand have been added to the mix. If higher than 60 percent, it is unfinished or immature compost containing undecomposed organic materials.

Be aware that each batch of compost that a producer makes varies in its analysis. One time the salt levels may be acceptable and the next time they may be too high, so check the analysis each time you purchase compost even if it comes from the same supplier or producer.

While local soils often benefit from the addition of quality compost, it is possible to over do it. Too much compost can cause problems including excess nutrient levels, especially nitrogen and phosphorous, high soluble salts, and excessive levels of organic matter. (Levels of organic matter above 5% to 8% by weight are too high.)

The general rule of thumb when adding compost to the soil in vegetable gardens or annual flower beds is to add no more than 2 to 3 inches of quality, low-in-salt compost to garden. The compost should be thoroughly incorporated into the top 6 to 8 inches of soil before planting. Done annually, the level of organic matter in your soil will increase. To avoid excessive levels of organic matter, reduce the amount of compost you are adding to only 1 inch after three years or get a soil test to determine the level of organic matter in your soil. As with so many things in life, too much of a good thing can be bad. The same goes for compost.

Garden Hint: How much compost do you need to apply one inch to the garden? Three cubic yards will cover 1,000 square feet to a depth of one inch.



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