Living SoilWhen the last tomatoes come out, what do you do with the beds? Pull everything, rake them bare and leave them until spring? Or leave it all standing and hope for the best?
Here is the part most gardeners miss. Fall is not the end of the soil's year. One extension page calls it the best time to add organic amendments, and compost, leaves or aged manure added now can decompose over winter, ready for spring. A bare, raked bed gets none of that, and is left open to erosion.
The big idea: putting a bed to bed for winter means three things: take out what carries disease, feed the soil, and cover it. Everything else is detail.
Fall garden cleanup: what goes and what stays
Disease is the reason to clean up. Many diseases can survive the winter on small pieces of leaves and stems, and diseased plants left over winter can supply fungal or bacterial spores waiting to infect next year's plants. Take those plants out, and keep them out of the compost pile too, because fungal spores can persist.
Healthy plants are different. Instead of pulling them, one extension page suggests cutting them off at ground level and leaving the root system in place. That reduces soil disturbance while adding organic matter, and organic matter is what soil life feeds on. In borders, leaves from healthy plants can stay where they fall.
Perennial stems are worth a second look before you cut them. Many wild bees lay their eggs in the stems of perennials, and leaving the stems until spring gives those native pollinators a chance to hatch.
Add compost in fall, and let winter do the work
Fall is the time to feed the soil. Well-rotted manure, leaves, compost and disease-free garden waste can all go on now, and compost, shredded leaves or aged manure can be turned into the soil to decompose over winter. If you are mulching in fall for a spring planting, one extension guide says you may even use green, non-composted material.
Three cautions:
- Manure must be aged. One extension page says all manure needs to be at least six months old, to prevent root burning and the possible transfer of human pathogens. Our article on manure in the garden covers the rest.
- Know where it came from. Manure, straw and hay may carry long-residual herbicides or troublesome weeds.
- More is not always better. One extension writer reports seeing more and more vegetable gardens with an excess of phosphorus, which can stunt vegetables. Another extension page advises holding off on organic matter or fertilizers until a soil test can guide you.
The living soil reason for all this: microbes need a constant supply of organic matter, or their numbers decline. Fall, with its leaves and spent plants, is a natural time to give it.
Should you till in the fall?
Here is where the sources differ.
- For fall tilling: one extension answer says a fall-tilled garden dries out and warms up more quickly in spring, so cool-season crops can go in earlier.
- Against it: one extension page says that if your soil has been improved over several years and is loose and soft to the touch, you don't need to till in the fall, and that over tilling breaks soil into very small pieces that remove air spaces and cause compaction.
For soil life, the wider research leans one way. Extension guidance on soil organisms says to till as little as possible, and one extension page says tilling compacts soil, destroys air and water pores, and can increase runoff and erosion. Another extension writer warns that rototillers, if overused, destroy soil structure and reduce soil organic matter. If your beds are already loose, there is little to gain. Our article on no-till gardening explains what tilling does below the surface.
Leaves: on top, or mixed in?
The sources differ on where leaves should spend the winter.
- Mix them in: one extension page says to mix leaves into the soil rather than leave them on top through the winter, so the soil is not kept too cold and wet to work in spring.
- Leave them on top: another says whole leaves can be layered on the soil and pulled back in spring to let it warm and dry. A third says to cover bare soil with shredded leaves to prevent erosion, and that the leaves reduce weeds and can stay as mulch next spring.
The mix in advice is about soil that stays too cold and wet to work in spring. If you would rather not dig, layering and pulling back in spring answers it without turning the soil. For pile, bag and lawn uses, see how to make leaf mold.
Sow a winter cover crop, or cover the soil
One extension page puts it plainly: don't leave the soil bare. A cover crop is the living way to cover it. Fall is a good time to plant one, such as winter rye, to improve the soil and reduce erosion. Timing is tight: in one extension guide, fall-sown cover crops go in during a two-month window, from mid-August to no later than mid-October. For a first try, or if you want to plant early in spring, the same guide suggests oats, which are killed by the first hard freeze and leave a brown, decomposing mat by spring. Too late to sow? Use shredded leaves or another mulch instead. Our guide to cover crops for home gardens covers which to choose and how to end them.
Winter mulch on perennials is a different job, with different timing. Its goal is to keep plants dormant, so it goes on after the ground is cold and plants are fully dormant: one extension page says to apply mulch after the ground freezes, and another gives a 3-6 inch layer of shredded leaves over tender perennials after several hard freezes.
The fall soil test
Fall is an excellent time to test your soil. Lime takes time to change soil pH, so one extension page says to apply it well before planting, a minimum of three months. But do not assume you need lime: soil pH can be too low or too high, depending on the soil. Apply lime or sulfur only if the lab recommends it. Most vegetable and fruit crops grow best at 6.0 to 6.8 pH. Our article on soil testing explains how to take a sample.
Where to start
- Clean up by health. Remove diseased plants, and keep them out of the compost. Cut healthy ones at ground level and leave the roots.
- Feed and cover. Spread compost or leaves, then sow a cover crop if you are still in time, or mulch the bare soil.
- Test now. Send off a soil sample this fall, and lime only if the lab recommends it.
When spring comes, read spring soil prep without tilling. For how soil life uses everything you add this fall, start with the living soil guide.