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Rotating crops helps vegetables, lessens disease, pests

Can you explain the principle of crop rotation? Is it applicable to flower gardening?

Crop rotation is a cultural practice used by farmers and gardeners to reduce disease and insect damage and to increase yields. When identical or alike crops are repeatedly planted in the same location, diseases and insects that feed on those plants will naturally build up in the area. This makes plants very vulnerable to attack. Also, because some plants are very demanding of specific nutrients, they can deplete the soil of these nutrients when they are repeatedly planted in the same location.

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With crop rotation, similar or alike plants are never planted in the same area in successive years. A rotation can be set up over two, three, five or more years depending on the crops being grown. For example, many farmers have fields of corn and soybean crops on a two-year rotation. In the first year, they plant soybeans in field one and corn in field two. In the second year, they switch fields and plant corn in field one and soybeans in field two. In the third year, they go back to having soybeans in field one, and so on.

A three-year rotation in a vegetable garden might have tomatoes in one area the first year, cabbage the second year and zucchini squash the third year. In the fourth year, tomatoes would again be planted in that area.

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Because many flowers are perennials, which remain in the same location for years, crop rotation is not as effective in the flower garden. However, it is not a good idea to plant the same annual flowers in the same location each year. This practice can cause some of the problems suggested above.

I am preparing a landscape plan for my yard, but the catalogs and books I am reading do not agree on proper tree spacing. How is tree spacing determined?

Tree spacing in a landscape is mainly determined by the expected mature size of the trees. However, the spacing can vary quite a bit depending on the effect you wish to create in the landscape. For example, I would plant red maples 30 to 40 feet apart if I wanted to use them as specimen trees. However, I might plant them 10 to 20 feet apart if I wanted to create a dense canopy like that found in a forested area. In addition, trees can grow quite differently from one location to the next, and various cultivars of the same tree can grow quite differently from one another. These factors also affect tree spacing.

Checklist

1. Remove from the garden vegetable plants that have stopped producing. This will decrease the risk of future disease and insect problems that overwinter on the plants.

2. To get the best selection of pansies, buy them now at your local garden center.

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, www.hgic. umd.edu.


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