Autumn Soil Boosters

Prepping garden soil in fall helps prepare it for next spring’s growing season

By Sara Bruskin

The end of the growing season is always a bit sad, but many gardeners are ready for a break when autumn rolls around—and the soil is, too. To prepare garden soil for next spring, follow these tips and your soil will be ready to weather the winter. When you’re planting next year’s garden, be sure to factor in crop rotation to keep your soil in the best possible condition.

1. Test Time, No Studying Required

Get your garden soil tested, especially if you’ve moved to a new gardening space. The Soil, Water and Plant Testing Laboratory at Colorado State University analyzes soil to determine its pH value, salt and nutrient levels. Testing is important, because adding amendments without knowing whether your soil needs them or not is a waste of money, and it can exacerbate existing problems. You can find the lab’s soil testing kits at The Flower Bin in Longmont, JAX Ranch & Home in Lafayette and McGuckin Hardware in Boulder. When you get your results back, bring them with you to your local garden supply store, where they can help you find soil amendments to address any issues.

2. pH Problems

A soil’s pH is a measurement of its acid-base balance. In moderately acidic environments, plants can more easily absorb iron, manganese, boron, copper and zinc. In more alkaline soil, plants readily absorb nitrogen, phosphorus, potassium, calcium and magnesium. Soil with a neutral pH is often ideal because necessary nutrients can all be absorbed to a significant degree. Beneficial soil microbes also flourish in this pH environment. Colorado has fairly alkaline soil, which can be nudged toward neutral pH with sulfur-based amendments, like aluminum and iron sulfates. But the changes will be subtle, so it’s best to grow plants that can tolerate a bit of alkalinity.

3. Compost Complete

Colorado has clay-rich soils, which are especially crucial to supplement with organic matter. Soil needs to be porous to drain, but Colorado’s packed-down clay is very dense. “Adding organic material will improve soil structure and increase microbial activity, which leads to stronger root development and improved nutrient uptake next season,” says Michael Morris, hardgoods manager at The Flower Bin in Longmont. He recommends adding 2 to 3 inches of compost to beds and working it into the existing soil. Compost helps aerate the soil and enables it to drain better, while slowly releasing nutrients.

4. Mission: Mulch

Watering in winter is still vital, as the soil’s microbes and mycelium will need moisture to stay healthy over winter. Mulch allows less moisture to evaporate from the soil’s surface, but there’s another reason to mulch in cold weather: “Winter mulching keeps the ground frozen by shielding it from the warmth of the sun,” Morris says. “A steady temperature will keep the plant in dormancy and prevent it from triggering new growth during a brief warm spell.” The Front Range’s extreme weather fluctuations, like those odd 70-degree winter days, can mislead perennials. It takes immense energy to put forth new growth, and that energy goes to waste when the weather turns cold again and kills off new shoots.

5. Grow Green Things

Cover crops add nutrients to the soil, help maintain moisture levels and prevent erosion over winter. Morris recommends planting winter rye, buckwheat or oats. “Cover crops help protect the earthworms and microorganism population by providing moisture and food through the winter,” he explains. Come spring, mix those plants into the soil to act as green manure, which will fix nitrogen levels and add organic matter.