Getting Your Soil in Shape
25 Mar 2013
Roughing up soil is the best way to make it healthy. Here’s a primer on amendments for this area.
BY CAROL O’MEARA Roughing up soil is the best way to get it in shape for both plants and beneficial microbes. Here are the best soil amendments for this area’s growing season.
Every gardener dreams of a verdant yard bursting with riotous blooms. So when spring finally warms the ground, we head outside and eagerly plunge a spade into the earth, where we run smack-dab into the concrete reality of Colorado soil. To put it mildly, it’s not a dream come true.
Heavy clay clings to shovel blades, pushing back attempts to dig deeper. Chipping away, gardeners labor to grub out the smallest of holes in which to tuck precious plants. Out of frustration, we employ pickaxes, consider backhoes, and in the end, realize the soil needs some tweaking before we can realize our dreams.
Organic amendments like compost, sphagnum peat and aged manure are great amendments for Colorado soils, as they create air pockets between the dense clay particles that are essential to vigorous root growth. When adding amendments, spread 2 inches of organic material on the soil and work it in with a shovel or rototiller it in to a depth of 4 to 6 inches. Remember, it takes years to properly improve clay soil, so amend soil for vegetables and flowers yearly, for trees and shrubs at planting.
Not all amendments are created equal, so here’s a brief primer on amendments to get your soil in shape. But the best first step is to get a soil test so you’ll know exactly what your dirt digs.
Helpful Amendments
Plant-Based Compost
For rich, crumbly, healthy soil, a long-term approach is crucial. In annual or vegetable beds, applications of plant-based compost over several years will build up organic matter, which is the most important material you can add to soil. Organic matter is usually low in Colorado soils—less than 2 percent. Ideal soil contains 5 to 6 percent. You can make compost yourself or purchase it in bags or bulk. Several compost sources are available, such as mushroom- or manure-based, but for low-salt, high-performance compost, stick with plant-based compost. Because it’s a source of organic matter, compost encourages the growth and well-being of soil microbes, creating a community that keeps soil rich and plants healthy. Though compost contains some nutrients, it isn't fertilizer. What nutrients it has are released slowly over time, so plants will need additional nutrient sources.Aged Manure
Traditional gardeners consider manure to be the ideal amendment. Cheap and readily available, manure builds up soil organic matter and adds nutrients, depending on its age. Composted manures often have small amounts of nutrients, while fresh manure can be high in ammonia. During composting, ammonia gas is lost from the manure, lowering nitrogen levels. But composted manure can be high in salt, so if your soil is already salty don’t apply manure. Be cautious about applying fresh manure to kitchen gardens, because of the risk of E. coli contamination. For gardens with edible crops, manure should be aged six months or longer before application.
- When adding compost to clay soils, either rototill or spade it in every spring to a depth of 4 to 6 inches.
Sphagnum Peat
Sphagnum peat is a good soil amendment, particularly for sandy soils, as it helps retain water and nutrients and its low pH is useful in our alkaline soils. Look for sphagnum peat sustainably harvested from Canadian bogs, which can re vegetate and grow back relatively quickly if they’re not over harvested. Avoid Colorado mountain peat mined from high-altitude wetlands; these sources take hundreds of years to rejuvenate, if they ever do.Biosolids
Bio-solids, or composted sewage sludge, add slow-release nutrients and organic matter to soil. Containing 5 to 6 percent nitrogen, bio-solids benefit the soil, but use this amendment in moderation as some brands are extremely high in salts. Check the bag or contact the distributor for an analysis; if the bio-solids have more than 10 ds/m (a measure of electrical conductivity), avoid them. Choose only Grade 1 bio-solids, which means the product doesn't contain excessive heavy metals and the pathogens have been killed. Also, never use bio-solids on root crops because of exposure to the plants’ edible parts. Make yearly applications of this amendment only if you routinely test soil for salt. Bio-solids are available from some communities or sewage-treatment plants, or in bags at garden supply stores.
- Never add sand to clay soil, which is the most prevalent soil in the Front Range. The dirt will turn to brick that plant roots won’t be able to penetrate.
