Hill Gardens of Maine - July 4th - Time To Feed Your Garden

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July 4th In The Garden
by Fred Davis, MG, Hill Gardens of Maine (To view other articles, click Archives)

Welcome through Fred's Garden Gate! While visiting a local hardware some year back, the proprietor asked an important question about fertilizer. Several customers had asked for a product called "Super-Phosphate," a particularly potent form of phosphorus (P, the middle number in the formula). The question: "What does this super-phosphate do for plants and when should it be used?"

Phosphorus, you'll remember, is the element which plants need to stay on schedule and produce abundant flowers--and therefore fruit or seeds. It's most common and least expensive form is rock phosphate, but is quite slow to break down to a form which plants can use. Bone meal is another form, much more quickly available but, by comparison, considerably more expensive. Super-phosphate is rock phosphate which has been treated with sulfuric acid to make it completely soluble in water and therefore much more readily available to plants - at significantly less expense.

For the average home gardener or small farmer, the temptation to use something which is fast acting and cheap is truly great. Organic farmers and gardeners, however, shudder at the thought of applying such a potent chemical...especially in their vegetable gardens. (An organic gardener prefers to avoid man-made or man-altered chemicals - to garden the natural way with composts, rock dusts and various animal wastes.) Large, commercial farmers were probably the first to take advantage of the new super-chemical. A common tactic was to use the natural but slower-acting rock phosphate for long-term soil building while applying a "healthy" dose of super-phosphate for quick results.

Super-phosphate, however, comes with a couple of down-sides. It is quite potent and can damage young plants if applied too heavily. It is also a salt and can eventually concentrate in the soil. Vast tracts of land in the southwest United States have or are fast becoming useless wastelands because of concentrations of chemical fertilizers - salt.

Actually, most garden soils already have an abundant supply of phosphorus but the plants simply can't get at it. You see, phosphorus is bound up with other soil elements - iron, for example - by low pH. In acid soils (the condition of almost all Maine and other northern New England soils), phosphorus locks itself to iron, (also abundant in Maine), aluminum and sometimes manganese, and becomes unavailable to plants. Think about it for a moment or two: if your soil is acidic (in the range of pH 5 to 6, or lower), you can pour on all the phosphorus in the world but it will do very little good.

A good excuse for finding out what the pH of your soil is, don't you think? Yet during the past twelve years of fielding hundreds of questions about gardening problems from visitors to our Maine gardens, very few of those gardeners had recently had their soil tested. Indeed, some didn't even know that there was such as thing as pH. A few couldn't have cared less.

Some customer-service-oriented nurseries have a little electronic gizmo that'll read soil pH in about 30 seconds, and will probably test your clean mason-jar-full for no charge. (If they don't or won't, they're missing a good bet!) A complete test can be obtained through the Cooperative Extension Service for a nominal fee.

Speaking of fertilizing, July 4th is an unofficial deadline for getting in the last feeding of perennials for the season. Nitrogen applied after about the middle of July can stimulate a surge of tender new root and foliage growth which may not have enough time to harden-up for winter. Remember to cultivate whatever fertilizer you use, into the soil...not simply sprinkle it on top. In our gardens we'll use a healthy application of compost plus a light feeding of 10-10-10. For sections of our gardens where we grow plants to eat, however, the fertilizer of choice is a blend of blood meal (nitrogen), bone meal (phosphorus), Jersey greensand (potash) and heaps of compost. Annuals and vegetables, of course, can be fed right up to harvest or frost, if you desire, because they'll not be expected to survive a New England winter.

This is also the time of year when maintenance is an important word for gardeners. Staking and tying; dead-heading; scouting for insect invasion and damage; searching for and destroying every weed in sight; and thinking seriously about contributing some of those excess vegetables to folks who may be in need, through your local "soup kitchen" or food distribution center. Seniors and shut-ins would also very much appreciate some fresh veggies...and a visit.

Additional reading: Fertilizer doesn't have to be complicated...and Sorting out the fertilizer puzzle.

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