Amendments for your Organic Garden

Greg Jubinsky showing the relationship
between vegetable plants and 
soil amendments

Recently I ran across a photo of market gardener and permaculture designer Greg Jubinsky which reminded me about the types of soil supplements you may need depending on the vegetable plants you are growing.  For an open house at Greg’s farm some years ago, he prepared a poster showing these important relationships which are summarized for you here. 

Most of the time adding compost several inches deep should supply all the nutrients needed in slow release form, which is ideal.  But if a soil test indicates you need nutrients or you want to give the compost a modest boost, this information should be helpful. 

For growing plants with fruit—Tomatoes, Cucumbers, Squash, etc., you need

    Less nitrogen (N) and more phosphorus  (P) and Potassium (K)

For growing leafy greens--Lettuce, Mustard, Brassicas, etc., you need

    More N, and less P and K

For root vegetables--Carrots, Radishes, Onions, etc., you need

    Less N, and more K

Amendments which supply Nitrogen (N):

Compost, animal manure (horse, cow, rabbit, chicken—and must be composted), Blood meal (strong, be careful not to burn young plants, water soluble), Alfalfa meal (also good source of P and K), Cottonseed meal and Soybean meal (Cottonseed meal is slightly acidic and slow release), Feather meal (moderate release rate), Fish emulsion and Fish meal (fast acting, especially in liquid form—apply with care as fast growing green crops attract pests), Green manure legume cover crops such as alfalfa, clover, peas, etc.

Amendments which supply Phosphorus (P):

Compost, Bone Meal and pulverized Rock Phosphate, Green manure cover crops such as Buckwheat and Lupine are good at mining phosphorus existing in the soil.  Unlike nitrogen which is pulled from the atmosphere by micro-organisms and supplied to legumes, minerals like phosphorus and potassium must exist in the soil to be accessed by cover crops.  In order to utilize the minerals mined by the cover crop, cut it and drop in place to decompose and release the minerals back into the soil.  (Additional Phosphorus is usually not needed in Florida soils.  A soil test can make that determination.)

Amendments which supply Potassium (K):

Compost, Seaweed, Wood ashes (alkaline), Greensand, Granite, Deep-rooted cover crops such as grains and daikon-type radishes which are good at scavenging minerals deep in the soil.

It’s also important to rotate your crops.  In addition to crop rotation, every three or four years or between seasons cover crops should be planted based on the vegetables you’ll be growing next. For instance, it’s good to grow field peas in the summer in places where you will be planting greens in the fall as the peas will leave behind nitrogen for the ensuing crop of greens. See the VegHeadz Crop Rotation Schedule for North Florida which takes these relationships into account.