Preen can be used in vegetable garden -- if you apply it at the right time


I use a product called Preen to control weeds in my flower beds. Can it also be used in my vegetable garden?

Preen is a pre-emergent herbicide that kills germinating seeds. It will not harm vegetable seedlings or kill established weeds. When Preen is spread evenly over the soil, it forms a chemical barrier that will prevent most weed seeds from emerging.

To be effective, it must be spread after flower or vegetable seedlings have been planted. If it is spread before planting, the planting process will break up the chemical barrier and weeds will grow in the disturbed areas.

Be aware that Preen and other pre-emergent herbicides will kill flower and vegetable seeds, just as it does the weed seeds. For example, plants like beans, lettuce, and carrots seeds are often directly sown in the garden and may be killed. If you plan to directly sow seeds, you will need to wait until after they all emerge and establish themselves before you put down Preen.

In general, I do not favor using herbicides in the vegetable garden. Most weeds can be controlled rather easily through cultivation and the use of mulch.

I planted three rhododendrons two years ago, and they have not bloomed. What can I do to make them bloom?

There are several reasons why rhododendrons might not bloom.

First, some rhododendrons don't bloom until they are about 5 years old. If you have young plants, give them another year or two in the same location to see if they bloom.

Second, there might be too much shade. Most rhododendrons like filtered light or partial shade. If your plants are in full shade, consider moving them to a brighter location.

Third, there might be excess nitrogen fertilizer. Excess nitrogen will cause plants to grow an abundance of leaves at the expense of flowers.

Finally, your plants might benefit from an application of phosphorus, but this would be very unusual in our area. Most of our soils have more phosphorus than is required for optimum plant growth.

To be certain, you can conduct a standard soil test. Test kits can be ordered from the Home and Garden information center at 800-342-2507.


1. Store excess garden seeds in a cool, dry place. One option is to seal open seed packets in a glass jar and place them in the refrigerator.

2. Stake your tomato plants now. It is easier to stake plants when they are small, and you will protect the young plants from damaging wind and rain.

3. Late-planted vegetables and flowers dry out quickly during warm periods of early summer. Be sure they are getting sufficient water.

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.

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