Amend soil with rock phosphate

Backyard Q&A

April 28, 2002|By Dennis Bishop | Dennis Bishop,Special to the Sun

Q. We are planting asparagus in our community garden plot and it was recommended that we incorporate rock phosphate into the soil before planting. What is rock phosphate?

A. Phosphate rock or rock phosphate is highly recommended by organic growers. As the name implies, it is mined from rock deposits for its phosphorus content (20 percent) and then used as a slow-release fertilizer.

It also contains a number of trace elements important to plants. After mining, the rock is ground into a very fine powder to prepare it for use on farms and in gardens. It can be purchased in bags at local farm and garden supply stores. Rodale Press recommends spreading 10 pounds of phosphate rock over every 100 square feet of garden space and allowing it to leach its way into the soil. It will be most effective if it is used in conjunction with manures. Apparently the manures help break the phosphate rock down into usable forms.

Q. I was purchasing geraniums at the nursery last weekend and the salesperson referred to them as zonal geraniums. What exactly is a zonal geranium?

A. The term "zonal geranium" refers to many varieties of annual geraniums that we purchase in spring for our pots and containers. Zonal geraniums might also be called common geraniums or garden geraniums.

Most of them have bands of deep red and green coloring on the leaves.

These bands are referred to as zones. This distinguishes them from the ivy geranium, which has a trailing growth habit and does not have the zonal bands. It also distinguishes them from the perennial geraniums, which are quite hardy, and bloom in late spring and early summer. The perennial plants are considered true geraniums and are in the Geranium genus. Zonal geraniums are in the genus Pelargonium, and are not considered true geraniums.

Dennis Bishop is an urban horticulture educator for the Baltimore office of the Maryland Cooperative Extension Services. If you have a gardening or pest problem, you can call the Home and Garden Information Center hot line (Monday through Friday, 8 a.m. to 1-p.m.) at 800-342-2507. You can also e-mail questions, order publications and diagnose plant problems by visiting the Web site, / users / hgic.


1. Lawns should be mowed more often during periods of rapid spring growth. Consider mowing every five days rather than the customary once a week.

2. Are you planting annual flowers this spring? Often, it is easier to mulch first and plant flowers through the mulch than it is to mulch around flowers.

3. Do not mulch right up to the base of your trees. A small, 1- or 2-inch-wide "mulch free" area will help prevent disease and insect problems.

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