Using more compost than necessary can create gardening problems. Depending on the compost origin and amounts used, soil minerals can actually become excessive and unbalanced. Correct ratios of minerals in the soil are important. Practices like “Lasagna” and/or “Square-Foot” gardening call for large amounts of organic matter. These are practices that will generally not yield vegetables that are dense in nutrients. With an excess of soil nitrogen, you often get excessive vegetative growth and poor fruit and seed development. Excessive use of compost can also raise the P, K, and Ca levels to more than are needed. Remember, if you keep a healthy (non-chemical) soil, it will be moving in the direction of increasing the organic matter on its own, through all the natural processes.
I have dealt with these issues with gardeners this past month. The AR Soil Lab would not even do a soil test on “soil” sent in from one Square-Foot gardener. The Soil Lab reply was, “send us some mineral soil, not just the soil mulch.” This does not surprise me. The recommended Square-Foot gardening “soil” material is all derived from various kinds of organic matter.
I have looked at many materials for advice on application of compost. The book, How to Grow More Vegetables, by John Jeavons is certainly one of the best for organic/sustainable gardening approaches. John recommends, “a maximum maintenance dressing of ½ inch of compost should be added to the soil before the crop per 4-month growing season.” That is equivalent to 4 cubic feet per 100 square feet of garden bed. I only recommend using high quality, mature compost. Cheap compost that is not fully decomposed is generally not a bargain.
For new beds in our typical NW Arkansas soils (where soil depths can vary from 6 to 20 inches), I recommend that you begin by double digging. In such cases, I recommend that you put 2/3 inch of compost into the lower layer and 1/3 inch on the surface. That equates to 40 and 20 gallons on each respective layer per 100 square feet. So, as you begin, 1 cubic yard of soil is enough for more than 300 square feet.
Tomato Time Hopefully, you have set your tomatoes out and they are doing okay. If you buy plants in tiny pots, I always recommend that you first move them to larger pots. See they picture below. Both plants are of same age (7 weeks), but note the huge (more than doubled-size difference), when the one plant on the left was moved to a 2-gallon pot when the plant was 6 inches tall.