How To Rejuvenate Garden Soil

I'm a soil scientist and a former faculty instructor for Oregon State University's Extension program, where I've taught and consulted with farmers and gardeners. My own half-acre garden in southern Oregon is my laboratory where I experiment to find new ways to improve the soil.

After spending years learning how to make garden soils light, fluffy, and easy to work, I wrote Building Soil: A Down-to-Earth Approach, a guide to everything you need to know to improve soil. Here are 10 of my top tips to improve soil:

1. Feed it an Organic Diet

Above: Florist Clare Day raises her own organic flowers on her 12-acre farm in British Columbia. See more at Organic Flowers at Red Damsel Farm.

Spring brings a flurry of underground activity that we can't see. Billions of soil organisms stretch and yawn, exploding into existence. It's this living soil below ground that helps gardens thrive above ground by recycling nutrients, capturing water, improving soil tilth, and fighting pests and disease.

We build soil health all year-round by feeding and caring for it. How? Living soil has the same four basic requirements we do: food, water, shelter, and air.

Autumn is the best season to start. Organic materials, the key ingredients for healthy soils, abound. You can add fallen leaves, garden debris, kitchen scraps, and even apples raked from beneath fruit trees to soil.

Chop organic material directly into the top 2 inches of soil with a heavy bladed hoe and cover with mulch. Ideally, add concentrated manures, mineral phosphorous and potassium fertilizers, and lime at the same time. Adding these materials in the fall gives them time to break down for use when plants need them in the spring.

2. Till With Worms

Above: Photograph by Jim Powell for Gardenista. For more, see DIY Composting: A Man Obsessed.

Instead of breaking out the rototiller, or breaking my back double digging, I like to let the worms do my tilling for me by using sheet mulching techniques.

Sheet mulching is the process of building compost right on the soil surface. For new gardens, I'll add a smothering bottom layer of cardboard to kill existing vegetation, then alternate 2- to 4-inch-inch thick green and brown compost layers. This invites worms to burrow through the soil as they transport food. In the process, they dramatically improve soil structure, while depositing power-packed worm manure castings.

Sheet mulching takes advance planning. Ideally, start sheet mulches for new gardens the year before you plan to plant (and for existing gardens a few months before planting). Sheet mulching will build new garden soil literally from the ground up. It maximizes nutrients, smothers weeds, and keeps soil life intact and undisturbed.

3. Grow Your Own Soil

Green manures and cover crops—such as buckwheat and phacelia in the summertime and vetch, daikon, and clovers in the fall—are my favorite way to improve soils. Whenever I have a window before planting, I grow a cover crop to add organic matter, lighten and loosen soil structure, and enrich garden nutrients. Cover crops also act as a living mulch to shelter soils and control weeds in the off-season.

Chop over-wintered cover crops directly into spring soils a few weeks before planting. During the growing season, sow a quick-growing cover crop, such as buckwheat, to fill the gap between spring and fall crops. When it's time to plant, pull the buckwheat cover and use it as a mulch for fall garden beds.

4. Test for Success

Above: A Soil Test Kit in a sturdy plastic case is $20.95 from Home Science Tools.

Soil tests are an indispensable garden tool. I always recommend taking one when starting a new garden, or when garden health declines. If an essential nutrient is missing, garden and soil health will suffer. For best results, take nutrient tests in the late summer or early fall. Submit a soil test to a certified lab to add the right balance fertilizers and lime materials to new gardens. For a list of certified labs visit NAPT.