In the last month, I've received calls and emails asking about what should be done to prepare the garden soil in the spring once the ground is no longer frozen and ready to be worked for the gardening season. Questions include what fertilizer should I apply, can I apply manure to my garden, if I do apply manure should it raw or composted, what about peat moss or should I use regular compost?
Out of the gate, the first thing I ask is if a soil test done. A soil test gives us a starting point for what our soils might need. I sometimes look over soil tests, and I see extreme amounts of potassium and phosphorous already present in the soil. These excessive levels could cause problems for your plants, inhibiting growth or yield or limiting uptake of other nutrients. In situations like those, it's recommended to avoid adding the nutrient in excess and to retest in a few years to see how things are looking.
The other question I often get is how much lime I should add to my soil. The answer to this is straightforward -- until you've had a soil test don't apply any lime.
Lime affects soil pH by raising it, and pH directly relates nutrient availability in the soil. Different plants have different pH requirements. For example, if you want to plant blueberries, before you get started it's important to have a soil test done. Blueberries prefer acidic or low-pH soils about 4.5 to 5.5, and lowering pH is accomplished through applying sulfur (not lime). In our area, a lot of the soils are close to neutral (7.0). If you want to plant blueberries, you need to have time for the soil pH to change after applying material and incorporating it into the soil the season before.
Depending on where the pH level is and where you want to get to (if change is necessary) will determine what product and how much to apply. Check with your local Extension office for advice on amounts after obtaining a soil test or if application is necessary depending on what you want to grow.
As for adding compost to your garden, it's a great way to improve soil quality -- in structure, texture, water-holding capacity and improving heavy clay soils, just to name a few assets. You can apply 2 to 4 inches of compost to gardens and, if possible, till it in. Otherwise, you can carefully incorporate it around existing plants.
If you are curious about using manure in your garden, the recommendation is to apply well-composted manure. This is because of concerns about potential E. coli contamination on edible crops. If you do want to apply manure, it's also best to incorporate it into the garden in the fall or early spring. If you want to apply composted manure to your garden, here is some other advice from Sandy Mason, University of Illinois Extension master gardener state coordinator, from her article "Using Manure in the Garden" (web.extension.illinois.edu/cfiv/homeowners/000513.html):
º Don't use manure around plants during the active growing season.
º Mulch the soil thoroughly to keep vegetables and fruit off the ground. Straw, shredded leaves or wood chips limit the produce's contact with the soil, as well as splashing from the soil surface.
º Wash all produce thoroughly before eating, especially root crops such as carrots, beets, radishes and onions. Do not use soaps unless specifically formulated for produce.
º Roots that appear rotten should be discarded.
º Think of the manure more as a soil conditioner than as a plant fertilizer. Manure adds organic matter, which is important for plant growth. However, most animal manures have low nutrient levels, and it takes a large quantity to produce good growth.
º Don't apply manure fertilizer within two months before harvest.
º Grow plants on supports as much as possible to keep produce off the ground.
º Wash your hands thoroughly before preparing and eating any food.