Fall Garden Bed Prep: Clean Up and Feed Soil for Winter

The Fall Routine in Five Jobs

Fall bed prep comes down to five jobs done in order: clear out the spent crops, take a soil sample, adjust the pH if the test calls for it, spread one or two inches of compost or shredded leaves, and cover the soil with a cover crop or mulch before winter. Lime is the reason to do this now and not in April. Clemson’s soil specialists note that liming material can take three to four months to change soil pH, which makes fall the time to apply it for next spring.

The same routine works for raised beds and in-ground rows. Flower borders are handled differently, and the section on stems and leaves below explains why.

Clear Out Spent Vegetables and Weeds

Start by removing what is left of the season’s annual crops along with any weeds that have come up. Oregon State University Extension is blunt about vegetable beds: remove everything, because pulling spent plants reduces the risk of soilborne diseases that can persist for years.

Sort the debris as you pull it. Healthy plant material can go on the compost pile, according to University of Illinois Extension, while diseased plants should be completely removed. Oregon State adds that diseased material should never go into home compost. That covers tomato vines with blighted leaves, mildewed squash and anything else that looked sick in August. If your pile has its own problems, the fixes in why a compost pile smells bad are worth a look before you add a season’s worth of vines.

Pick up fallen and leftover fruit too. Oregon State notes that clearing it from the trees and the ground cuts down on next season’s disease and pest problems, apple scab and codling moth among them.

Containers get the same treatment. Illinois Extension suggests tossing the old roots and potting media on the compost pile and cleaning the pots with a mild bleach solution of 10 parts water to one part bleach.

Leave Some Stems and Leaves Standing

Vegetable beds are cleared. Perennial borders are better left partly standing. Oregon State lists ornamental grasses, coneflowers, Joe-Pye weed, sedum and black-eyed Susan as plants that provide winter habitat for insects and seeds for birds.

Stems matter to native bees in particular. An Oregon State guide on bee habitat recommends leaving an extra 8 to 10 inches of stem when you cut back plants with pithy or thick stems, such as raspberries, elderberries, hydrangea, coneflowers, sunflowers and asters. The next generation of bees emerges from those stems the following spring. University of New Hampshire Extension goes further and suggests leaving stalks up all winter, then cutting perennials back to about fifteen inches above the ground in spring.

Fallen leaves do a similar job. New Hampshire’s guidance points out that the leaf layer shelters and insulates pollinators that overwinter in it. Rake leaves off the lawn and paths, and let them lie under shrubs and in the back of borders.

Test the Soil and Adjust pH in Fall

University of Wisconsin Extension calls fall a great time for soil testing, provided the soil is not too wet. The report will include soil pH and, where needed, a lime or sulfur recommendation. Our guide on how to read a soil test report walks through the other lines on it.

To take the sample, University of Vermont Extension suggests collecting soil from about ten random spots across the garden, each dug 6 to 8 inches deep, and mixing them. Wisconsin gives the same 6 to 8 inch depth.

Most vegetable plants prefer a slightly acidic soil pH of 6.0 to 6.5, according to Clemson. If your result is below that range, the lab’s recommendation tells you how much lime to use. As one regional example, Oregon State advises 5 pounds of lime per 100 square feet when vegetable garden soil tests below pH 6. Rates differ by soil type, so follow your own report where it gives one. Clemson adds that lime is most effective when it is tilled into the soil, and that dolomitic lime supplies magnesium as well as calcium.

Soils that test too alkaline are treated with elemental sulfur, which can also be applied and worked in during fall.

Spread Compost and Hold the Nitrogen

Once any lime is in, spread one or two inches of homemade compost or shredded leaves over the soil surface. Vermont Extension suggests leaving that layer in place over winter and working it into the soil in spring.

Fertilizer is a different matter. Vermont’s advice is that apart from materials that adjust pH, all other nutrients, especially nitrogen, should wait until spring.

If you are starting a bed from scratch this fall instead of renovating one, the sequence in building healthy soil for a new garden bed covers the first-year steps.

Sow a Cover Crop Before the Window Closes

A cover crop holds the soil over winter and adds organic matter when it is cut down. University of Maryland Extension says fall-sown cover crops are typically planted in a two-month window that starts in mid-August and ends no later than mid-October. That window is written for Maryland, so gardeners farther north should aim for the early end. Choosing a species for each bed is covered in more depth in cover crops for a small vegetable garden.

Maryland’s seeding rates for a home garden are small enough to measure on a kitchen scale.

Cover crop	Seed per 100 square feet	In spring
Winter rye	3 to 4 ounces	Cut down before it sets seed
Winter wheat	3 to 4 ounces	Cut down before it sets seed
Spring oats	3 to 4 ounces	Already winter-killed, leaves a dead mat
Hairy vetch	3 to 4 ounces	Cut down before it sets seed
Crimson clover	1 to 2 ounces	Cut down before it sets seed
Forage radish	1 to 2 ounces	Already winter-killed, leaves a dead mat

For a mixture, use about 60 percent of the recommended amount of each. Broadcast the seed by hand, preferably before a rain, rake it gently into the surface, then walk over the bed to press the seed into the soil.

Rye is the pick for a late sowing. Maryland notes that winter rye can be planted the latest in fall, and Penn State Extension’s page on cereal rye as a cover crop notes that it germinates at temperatures as low as 34°F. Spring oats and forage radish suit gardeners who want an early start in spring, because both die in the cold and leave a mat of dead vegetation that can be planted through.

Mulch the Beds You Cannot Sow

A bed that was cleared too late for a cover crop should still not sit bare. Vermont Extension notes that an inch or two of mulch protects the soil over winter. Shredded leaves are the cheapest material in most yards. Oregon State recommends spreading leaves over vegetable beds to help prevent compaction from winter rains, suppress weeds, boost fertility and improve soil structure.

Illinois Extension suggests a second use for the surplus: rake extra leaves into a pile near the garden so they are on hand as mulch next spring and summer.

Plan the Spring Handoff

Overwintered cover crops have to be killed before they set seed. In Maryland that means mowing, flattening or turning them into the soil in late April or early May. Allow about 2 weeks for the residue to break down before planting, which can delay early spring crops. Beds sown with oats or radish skip that wait.

Timing matters most with rye. Penn State notes that once rye reaches its reproductive stage and its carbon to nitrogen ratio passes 40, soil nitrogen is not readily available to the next crop as the residue decomposes. Cutting it while it is still leafy avoids the problem.