Feeding Cole Crops
Although they're heavy feeders, cole crops don't have special fertilizer needs; a moderate dose of a basic commercial fertilizer is fine. Work it into the transplant hole for seedlings or, for seeds, the top 3- to 4-inches of soil on planting day.
Chemical fertilizers supply the three elements that are vital to plant growth. These are nitrogen, phosphorus and potassium. Their presence in a bag of commercial fertilizer is indicated as a percentage of the total (for instance, 10-10-10 or 5-10-10). The elements are always listed in the same order: nitrogen (N), phosphorus (P) and potassium (K).
Organic fertilizers, such as dehydrated animal manures, are also excellent sources of plant nutrients. They should be mixed into the soil at the same time and at the same rate as chemical fertilizers, about 5 to 6 pounds per 100 square feet. Organic fertilizers also condition the soil while providing nutrients to the plants.
No matter what type of fertilizer you use, if you know your soil is already very rich in organic matter such as leaves or compost, you can add a little less fertilizer. You may want to try a combination of organic and commercial fertilizer in your garden. The organic material conditions the soil, and the plants get their fair share of nitrogen (which aids in leaf and stem growth), phosphorus (for strong roots) and potassium (for the overall health of the plant).
When planting seedlings, take special care not to overfertilize. Even after hardening, transplants are tender, and if they grow too fast when you first set them out, they may be weak in the long run. It's better to go easy on the fertilizer when they're transplanted and side-dress later in the growing season. Use only a small handful of fertilizer for each plant at transplant time.