Q: I’ve heard that crop rotation is an important factor in successful vegetable gardening. What should I know before I implement a crop rotation plan?

A: Crop rotation has been considered a fundamental principle by farmers for many years and is a good practice for home vegetable gardeners to control soil-borne diseases and insects. For example, if you plant tomatoes and related crops in the same bed only once every three to four years, you can help prevent diseases caused by fungi that remain in the soil over the winter.

Crop rotation helps build up the organic matter and soil nutrients that vegetable plants use during their growth and production cycles. Some crops, like cucumbers and tomatoes, use lots of nutrients, while others, like beans and potatoes use less and may actually add nutrients to the soil.
Experts recommend a three- or four-year rotation plan, giving consideration to grouping crops by heavy or light nutrient needs and their ability to add organic material to the soil. A simple rotation plan, just keeping a notebook of where your crops are planted from year to year, can help keep your soil balanced and your garden healthy.

Q: When and how should I divide my bearded iris plants?

A: Bearded iris should be divided and re-planted when you begin to observe the clumps becoming over-crowded, or spreading too far from their intended location. Dividing and re-planting helps ensure good plant health and better blooming performance. The best time of the year to divide and re-plant bearded iris is after the current blooming cycle.

Using a spade fork to minimize root and rhizome damage, loosen and gently pry the clump from the soil. Wash the remaining soil from the rhizomes and inspect the clump. Use a sharp knife and cut the younger rhizomes into segments with healthy roots and one or two leaf blades. Trim the leaf blades into a fan shape and plant the rhizome no deeper than one inch, making sure to spread the roots out evenly.

Q: I have dead patches, shaped like “donuts” or “frog-eyes” in my Kentucky bluegrass lawn. What’s wrong and what should I do about it?

A: You may be seeing the primary symptom of necrotic ring spot (NRS), a perennial problem in Kentucky bluegrass lawns. The fungus that causes NRS colonizes the bluegrass roots when soil temperatures range between 65 and 80 degrees, and can survive from year to year on dead root and crown tissues. As the infected turf loses its ability to absorb moisture and nutrients, symptoms often appear in spring or fall, but may persist during summer.

Management practices include moderate fertilization at one pound of nitrogen per thousand square feet, using a combination of slow- and quick-release nutrients. Spring and fall core aeration, mowing at 2-1/2 to 3 inches and avoiding over-watering are also important in preventing and managing NRS. For more details, refer to Fact Sheet #2.900, “Necrotic Ring Spot”

Gardening and Insect Fact Sheets are available on-line by clicking HERE.

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This page updated:  June 5, 2007