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GARDENING Q&A

What Numbers Mean in Plant Food Labeling

May 29, 1994|JACK CHRISTENSEN | SPECIAL TO THE TIMES

QUESTION: What is a "balanced plant food," and what do the numbers on plant food containers stand for?

ANSWER: Nitrogen, phosphorus and potassium (or N, P and K respectively) are required by all plants and affect plant growth in rather specific ways. "Balanced plant foods" contain all three of these nutrients in various proportions, depending on how they will be needed.

The package label displays a three-number formula (such as 8-10-6 or 12-12-12) identifying the percentage of each nutrient in that blend of plant food.

The first number in the formula always stands for nitrogen, which promotes greenery and leafy growth in plants. (There are two types of nitrogen in plant foods, identified in the "Guaranteed Analysis" on the package label: slow-acting, longer-lasting "ammonia" or "urea" forms, and fast-acting, short-term "nitrate" or "nitric" forms. Slow-growing plants such as camellias prefer the ammonia form, and fast-growing plants such as roses prefer the nitrate form.)

The second number is the percentage of phosphorus, used by plants in roots, flowers, fruits and seeds.

The third number represents the amount of potassium or potash in the plant food. This nutrient is required for healthy stems and proper growth.

Knowing this, it's easy to decide which of the many available formulas are best suited to the needs of your plants, as long as you know what you want your plants to do.

For instance, you want your lawn to grow lots of greenery, so you should use a plant food highest in the first number, such as 12-6-2 or 10-6-4 or 8-4-2. The same is true for growing lettuce or cabbage or celery in your vegetable garden. (Lawns grow fast, but they are intended to last a long time. Therefore, it is best to feed lawns with blends containing both the ammonia and the nitrate forms of nitrogen, for both immediate and lasting effects. Most vegetables grow quickly and benefit from the quick-acting nitrate forms of nitrogen.)

Roses grow vigorously, producing lots of flowers on new shoots. To promote optimal bloom they require a formula such as 15-30-15 or 8-12-6, highest in the middle number, with the faster-acting nitrate form of nitrogen. Camellias grow slowly, producing their flowers on mature wood; they benefit from a similar formula that uses the slower-acting ammonia-type nitrogen. Similar formulas highest in the middle number should be used on any plants intended to bloom heavily (such as hibiscus, day lilies and irises) or produce fruits (squashes, peaches, oranges, avocados) or seeds (peas, beans, almonds, pecans) or edible roots (potatoes, turnips, onions). It's fairly easy to decide which type of nitrogen should be in the formula just by knowing how fast the plants grow.

Plant food formulas highest in the last number are never really needed and are not normally available on a commercial basis.

One last word of advice: When using plant foods, be sure to apply them in accordance with the manufacturer's instructions, because an overdose can be lethal. Just enough will save money and will give wonderful results.

How to Prepare Soil for Planting Garden

Q: How should I prepare my soil for planting vegetables and flowers?

A: In this arid, semi-desert climate our soils desperately lack organic matter, which would significantly improve their water-holding capacity and help keep essential nutrients available for plant growth.

Gardeners here are wise to amend their soil with humus, leaf mold, composted rice hulls, aged manures, shredded forest materials and other such products to save water, to maximize their harvest and to increase the efficiency of their own efforts.

I do not recommend the use of redwood or peat-moss products in our area for the following reasons: redwood contains a component that may actually inhibit the growth of some plants, especially roses; and peat moss must be thoroughly moistened before use and never allowed to dry out. Once peat moss dries out in the soil, it becomes practically waterproof and may jeopardize your plantings.

To make a marked improvement in your garden soil, cultivate the ground to a depth of about 12 inches, then add 3 to 6 inches of organic amendment and mix it thoroughly into the soil by spading and re-spading or by rototilling.

This approach is both laborious and potentially expensive, but it will give amazing results and is truly worth the investment in time and money if you plan to do serious gardening on a long-term basis. Even so, any amount of organic material added to your soil will be beneficial.

How Does Vitamin B-1 Help New Plants?

Q: I've heard that Vitamin B-1 should be used whenever I put new plants into my garden or landscape. What does it do?

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