June 13, 2001
Stillwater Gazette
Betsy Halden

Chrysanthemums, black mulch and insecticidal soaps in June

Spring and summer care of chrysanthemums
It’s easy to focus on spring and summer plants in June, but our hardy Minnesota mums will be welcome bloomers in late summer and early fall. Our chrysanthemum plants by the driveway look good now, but they need care. While these colorful perennials are easy to grow, we need to pinch, water, and fertilize them if we want to have flowers in season.

Pinch newly planted and established mums from late spring to midsummer. Remove the stem tips when the shoots are approximately 6 inches tall. New lateral branches will develop along the stems. Pinch again when these new shoots reach a length of 6 to 8 inches. Pinching can be done with your fingers or a pair of clippers. Continue pinching until late June or early July. Pinching results in bushy, compact plants with additional flowers.

Water mums thoroughly during hot, dry, weather. Water deeply once a week. Avoid wetting the foliage when watering to discourage possible disease development. To conserve soil moisture, mulch chrysanthemums with 2 to 4 inches of grass clippings, wood chips, or other materials.

Encourage plant growth with a monthly application of fertilizer. Use a water soluble fertilizer according to label directions or dissolve 1 tablespoon of a complete garden fertilizer, such as 5-10-5, in one gallon of water.

Black plastic mulch
After writing about organic mulches several weeks ago, friends asked about black plastic mulch. You may be hearing gardeners talk about the benefits of using black plastic mulch around tomatoes, peppers and vine crops. According to the users, earlier and greater yields are the rule for black plastic mulches. Garden centers sell rolls of black plastic made just for this purpose. Most plastic mulches should be removed at the end of the year. Decomposition takes forever, unless you use the newer decomposable kind.

If you are wondering how you could actually use black plastic mulch here are some tips: Lay the plastic on bare soil. Dig small trenches and bury the edges with soil. Cut X's with a knife into the plastic for the plants. Keep plants low so water naturally runs into the plant. Slit low spots with a knife so water sinks in. Keep soil to a minimum on top.

Use of insecticidal soap on plants
Our neighbor told me the other night she had tried everything on her ailing hibiscus, including insecticidal soap. She asked if it was effective as other pest controls. Insecticidal soap is often thought of as a panacea. It controls a wide range of pests and it is generally safe to the gardener who is applying it. It is also more environmentally friendly than many pest controls. However, it can be quite ineffective and it can cause plant damage if it is not used correctly.

Insecticidal soap should only be used when pests are present. Insecticidal soap kills only when it comes in contact with pests. There is no active residue that remains on the plant after the soap has been used. The application must be thorough so contact is made to all intended pests.

As in applying any pesticide, never spray stressed or newly transplanted plants. Certain plants are sensitive to soaps. They include palms, certain ferns, begonias, Japanese maple, mountain ash, some geraniums, azaleas, and succulents. Check the label for others. If you want to be more cautious, spray only a small part of one plant and observe it for a day or two.

To use insecticidal soap, first put some water in the sprayer. Then add to the water the determined amount of soap recommended on the label. Avoid doing this vice versa. By adding the soap to the water you eliminate the need for agitation or shaking, thus reducing the amount of foam generated. As when any pesticide is applied, plants should be thoroughly doused on the upper and underneath sides of the leaf.

As with any insecticide, carefully follow directions on the label. Do not spray when a plant is in bloom. Do not spray when temperatures are over 90 F and sunny.

Do you know of events we could include on our gardening calendars? Please send an email with event, time, date, and location. We’ll include it in the calendar.

The Yard & Garden Line is a great resource for gardeners. Call the Yard& Garden Line at 612.624.4771 in the metro area or 888. 624.4771 in greater Minnesota. All services are free of charge except for sending samples or talking to the University Yard & Garden Clinic experts.

For timely gardening information visit the Yard & Garden Line News at www.extension.umn.edu.

Betsy Halden is a Master Gardener with the University of Minnesota Extension Service. University of Minnesota Extension Service materials were consulted in the preparation of this column. You can reach Betsy Halden at eahalden@comcast.net