Healthy soil is the key to healthy plants, whether you are growing Rhubarb or Roses, Carrots or Clematis vines. Most NW native soils are low in nutrients due to their high percentage of sand and our frequent rains, which leach the nutrients down below the level of plant roots, or wash them away. Compaction is also a major problem in many soils, with foot traffic and/or rain pushing all the air out of the soil. Adding a generous amount of compost and mulch to your soil will allow it to retain more air, nutrients, and summer water, yet still allow it to drain well during our rainy months. The microorganisms that live in healthy soil form a symbiotic relationship with plant roots, which adds significantly to their health.

Worm bin compost contains an incredible amount of microorganisms, and worm bins are a fun and easy way to compost your food scraps at home. For info on all the ways to make great compost at home, visit http://www.seattle.gov/util/Services/Yard/Composting.

Soil Amending

1. Where new beds are being created in open areas, incorporate 3 inches of organic compost to a depth of 9 inches prior to planting. However, do not do this in areas where roots of surrounding trees and shrubs fill the soil, as it will severely damage them. In these areas, just install 2 inches of compost on top of the soil, scratch it down into the top couple of inches, then let rain, worms, and other microorganisms incorporate it gradually.

2. Two other ways to add organic materials and nutrients to your soils are cover-cropping and sheet mulching. Cover crops are plants sown into the garden that are incorporated into the soil before they reach maturity. Many are legumes, which add more nitrogen than other crops. Sheet mulching is a longer-term approach, where layers of newspaper or cardboard are covered with organic materials and left to decompose for 6-12 months before being incorporated. This is a great way to turn lawn into garden over the long wet winter!

3. Most vegetables thrive in a soil with a neutral PH, and amending with lime can reduce the acidity of our native soils and add calcium, which is a vital micronutrient for most plants. It's best to get a soil test to check for PH before amending, but it is usually safe to add about 4 pounds per 100 square feet every 2-3 years. Some food crops such as Blueberries prefer acidic soil, as do many of our native ornamental plants, so don't add lime until you have determined what you will be planting and where.

4. Amending the soil each year with organic fertilizer is also important for healthy and productive annual food crops, most of which tend to be "heavy feeders". For great tips on how to apply the proper amounts, visit http://www.seattletilth.org/learn/getting-growing-with-a-good-fertilizer. If you are adding edibles to existing ornamental beds, remember to match their fertilization needs as well. IE: Root or fruit crops need less fertilization than leafy greens, so Strawberries or Garlic are well-suited to grow in the root zone of an established shrub, and Lettuce or Spinach good under Roses which are also heavy feeders.

5. Mounded or raised beds allow soil to warm up earlier in the spring, and improve drainage. You can use the soil dug for the pathways to add to the height of your mounds, or purchase good quality topsoil that contains sandy loam and organic compost. Keep in mind that the mounds will eventually settle to a lower height than when originally created, so build them slightly above the ultimate height you want to achieve. It is also important to first loosen up the soil beneath the mound, in order to create good water permeability, drainage, and air exchange there too.

READ THIS BEFORE DECIDING TO BUILD ANY MOUNDED OR RAISED BEDS
Raising the soil height more than a couple of inches over the top of the root zone of established trees and shrubs can cause restricted air movement for their far-reaching roots, and result in stress, decay, and long-term health problems. It can take years for any symptoms of decline to appear in the canopy, and in some cases can cause death of mature trees and shrubs. It is especially important to be conservative before adding mounded beds near all members of the Rhododendron family, which have a very shallow, wide root system and are easily suffocated.

Mulching

Mulch is a very important element in building healthy soil, because it conserves water in the soil during our dry summers, helps to control weeds, and slowly feeds the soil as it decomposes.

In a vegetable garden, it is important to use organic materials that can be eventually incorporated into the soil. Fall leaves, straw, or grass clippings are good mulching materials because their coarser texture also helps prevent compaction by winter rains, but you can also just use a layer of compost as mulch.

Coarse wood chips are best for mulching fruit trees and berries, as well as ornamental shrub beds, as they also help prevent compaction by sun, rainfall, pets, and humans. For the same reason, wood chips also make great path surfaces between vegetable beds. However, it's very important to allow the chips to decompose on the soil surface but not turn them under, as they will temporarily "steal" nitrogen if incorporated down into the soil, which can damage nearby plants.

Finely-shredded wood chips or beauty bark are not good mulch materials, as they knit together quickly to form a compacted and impenetrable barrier to water and air, and an inhospitable environment for beneficial insects, worms, and other beneficial soil organisms.

All mulches of any type should be kept 3-6 inches away from the trunks of trees and shrubs, and the crowns of perennial plants, in order to maintain good air circulation, which is vital to long-term plant health. Buried crowns and trunks are one of the primary causes of plant decline and death, and can develop for many years before showing visible (and many times irreversible) decline in their flowering, leaf growth, and canopy.

For info on using compost and mulch throughout your landscape, visit http://www.seattle.gov/util/Services/Yard/Natural_Lawn_&_Garden_Care

All photos on this page are the property of Emily Bishton