Growing Concerns 559: What, when, how of fertilizer


All things that will decompose in the soil are organic fertilizers


Dear Janet & Steven,

Tell me about fertilizers, please! What do you fertilize with? When? How?

I want to try to use organic gardening methods. Which fertilizers will do the trick that are organic? - M -

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Dear M.,

The ideal time to fertilize is when plants are most actively growing, such as in spring when houseplants resume growth, as outdoor plants leaf out for the year or in summer when fruit is growing rapidly. The trouble is that every plant has its own timetable. The snowdrops in our garden are forming seed now, yet the Japanese anemones that occupy that same space aren't even stirring yet. The cranberrybush viburnum that overhangs and underlies that whole area won't reach its greatest need for fertilizer until June and July as it forms a new crop of brightly colored fruit.

Rather than trying to keep up with all these plants individually, we apply a slow release fertilizer made from poultry manure to the whole bed in spring or in fall, spreading it on the surface and then covering it with mulch so it will become available to the plants a little at a time, whenever the soil is warm enough that its microorganisms and "soil animals" can digest it. Sometimes we follow up with a water soluble fertilizer during summer for the heaviest feeders. Miracle Gro can serve this purpose, or fish emulsion or seaweed solutions.

Photos at right: What's the common link between all the plants and plant categories shown here? They're all in active growth and so nutrients are as critical to them as vitamins to a growing human child. These new leaves will never match the size, color, flowering-/fruiting ability and natural pest resistance of the mature foliage unless the water coming up to it now has come from soil with an ample supply of nitrogen, phosphorus and potassium. (Top to bottom: Common houseplant Schefflera arbicola a.k.a. umbrella plant resuming growth after the winter stall, American beech leaves (Fagus grandifolia) expanding in April, perennial daffodils emerging in spring, and annual seedlings of annual flowers and vegetables.)

Fertilize to correct the soil's lack, not the plant species


The ingredients in fertilizer aren't plant food. Plants make
all of their own food by creating sugar and starch from sunlight, water and air. As they grow, the plants incorporate various minerals from the soil. Fertilizers are mixtures of those nutrients. They are the equivalent of vitamin supplements for the soil. The best fertilizer is one that supplies what the soil around that plant's roots might not have in enough quantity to meet all of the plant's needs.

Most soils have all of the minerals a plant may need, but to grow to its full potential a particular plant may need elements in different proportions than what that soil will provide. A soil test will tell you what to add for your soil to produce a good crop of lawn, flowers, shrubs, Christmas trees, etc.

The soil in our yard tests fine for most elements but is a little low for potassium, so soil test results recommended adding relatively more potassium than other elements. If
we didn't have the test, we would apply a fertilizer with equal amounts of nitrogen, phosphorus and potassium, such as a 10-10-10 granular that has ten percent of each of those major nutrients, or a 2-2-2 dried cow manure. All of these are called "complete, balanced" fertilizers for their
1-1-1 ratio of major nutrients.

Since we do know our soil's deficient in potassium we use a balanced fertilizer plus some greensand, which is six percent


potassium, 0-0-6. Alternatively we could use the balanced fertilizer plus muriate of potash which is 60 percent potassium, 0-0-60.

Organic in fertilizers means carbon and less processing

Organic growers use raw materials as fertilizers rather than granulated processed chemicals. To grow organically and add potassium, use the greensand rather than muriate of potash, since greensand is a simple rock powder but the other has been treated with chemicals to make more of its potassium water soluble.


What counts as an organic slow release fertilizer? Manure, cottonseed meal, coffee grounds, decaying leaves, bark mulch and anything else that will decompose within the soil. They don't "melt" into water like processsed, salt-based fertilizers but release their constituent chemicals gradually as bacteria, fungi, insects and worms digest them.

These organic materials also add carbon, which becomes humus and beefs up the structure of the soil. That increases the soil's ability to hold water and nutrients.

You can rely on compost or leaves for fertilizer but these are relatively low in nutrients so you must use them in large quantities and encourage their decomposition. Also, you won't know for sure how much of the essential elements you're adding. To supplement a specific soil , buy packaged organic products that have been tested for nutrient content and labeled as fertilizers. These are available at many garden centers. You can also look for retailers that specialize in organic additives. (Do these all have quaint names, like our local Chelsea Farm Co-op or Uncle Luke's Feed Store? Maybe!)

Short reports

Finding shrubs were mashed under snow banks?

Don't try to bend or tie branches into place now. Prune off what's broken, water well and wait for the plants to leaf out. Then prop the branches -- by stages if necessary -- into better positions if they don't rebound on their own as the sap rises. As this year's leaves mature, new wood will form in the branches. That's when they need to be in your desired alignment.

Why not suggest peat pellets in Styrofoam cups...

... for that person who wasn't much of a gardener but wanted to start seeds with young children? Asks S.B., who also points out,  "Those peat pellets are found everywhere.  They are cheap and easy to start seeds with no mess for the novice as well as weekend gardeners." Good idea, S.B.


Green thumbs upRabbitDungN6846s.jpg

to all the rabbit pellets on our lawns and gardens. That's organic fertilizer of the
highest order.

Right: See the droppings on the ground below the badly chewed canes of dwarf burning bush (Euonymus alatus 'Compactus')?
That's rabbit dung!


Green thumbs down

to all the damage those hungry rabbits did to shrubs and trees. It's an expensive way to fertilize!












Originally published 3/20/04; updates 4/2/14








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