Increase Next Year’s Vegetable Production with Fall Soil Care
Diana Alfuth
UW-Extension Horticulture Educator
Probably the biggest thing you can do now to have a great and productive garden next year is test your soil and amend it as needed.
The better your soil, the better your plants! There are three types of “fertility” that your soil has: Physical fertility, chemical fertility, and biological fertility. All three are necessary to grow healthy, vigorous plants that produce lots of tasty, healthy vegetables.
Physical fertility refers to the texture and structure of the soil. Whether you have sand or clay as the major component of your soil, you can amend it to improve productivity.
Plant roots need not only water to grow, they need oxygen, which permeates from the soil surface through the little air pockets in the soil. Without oxygen in the root zone, plants can’t take up water and nutrients. The ideal soil will have about 45 percent sand, silt or clay particles, 25 percent air pockets, 25 percent water attached to the particles, and 5 percent organic matter. Organic matter is anything that was once a plant. It comes from roots of plants that have died off, or from compost that has been added to the soil. It’s important to protect your soil structure by avoiding excessive rototilling, compaction, and erosion.
Soil also has chemical fertility, which includes all the nutrients plants need, such as nitrogen, phosphorus, potassium, calcium, magnesium and others. This is why we add fertilizer if the soil does not have enough chemical fertility. These nutrients are the “vitamins” the plants need to grow, and if they are short on any of their vitamins, they simply will not produce well.
Finally, but probably most importantly, soil has biological fertility. This refers to the tiny and microscopic microbes that live in the soil. Soil microbes include bacteria, protozoa, fungi, mites, and all kinds of other tiny things, as well as larger things such as worms, insects, and slugs. There are billions of microbes in a tablespoon of soil, and they perform extremely important roles of breaking down organic matter and releasing nutrients (vitamins) into forms that plants are able to take up. Without these microbes, the soil is basically “dead” and the plants would not be able to grow well, if at all.
Your goal as a gardener should be to build your soil so that you have a healthy and robust population of microbes. Microbes need the same things as any other living critter: food, water, and shelter. The shelter comes from good soil structure, the water comes from rain or irrigation, and the food comes in the form of organic matter.
To build good soil structure that has water, oxygen and plenty of food for a robust microbe population, gardeners should add organic matter each year. The general rule for a vegetable garden would be to add two inches of compost each year. If you don’t have enough compost available, there are other ways to add organic matter, including growing and incorporating cover crops and working in mulches. Because of microbe activity and decay of organic matter, there will be only about 5-10 percent left after a year. That’s why it’s important to add additional organic matter each year.
The other thing that is extremely important for growing plants is to have the correct soil pH. The pH is important because if it is too high or too low, plants will not be able to take up nutrients from the soil. Vegetables grow fine in a pH between 6.2 and 7.2. The only way to know for sure what the pH is is to test the soil.
While there are soil test kits available at garden centers, some of them are less than reliable. It is much better to send a soil sample into a quality lab to not only get an analysis of your soil, but recommendations of what to add. The University of Wisconsin soil testing lab, for example, will tell you how much phosphorus and potassium you have in the soil, what your pH is, and how much organic matter you have. It will also tell you how much fertilizer, lime or sulfur you should add to make the soil appropriate for the type of plant you want to grow.
Doing a soil test every 4-5 years is a small investment in a productive garden. Fall is an excellent time to do a soil test. After garden cleanup, incorporate necessary lime, sulfur, or organic matter so that those materials can break down a bit in the soil and you will be ready to plant in spring.
Building a healthy soil should be the first goal of all gardeners. Without it, you simply cannot have healthy plants and maximum production.
For more information on testing your soil and creating the perfect soil, contact Diana Alfuth, Pierce County UW-Extension Horticulture Educator, at (715) 273-6781.