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July, 2010                                                                    Number 40 
Soil temperature on July 1: 80 degrees                               Rainfall past 14 days: 0.60 inches
Ask a Master Gardener

Question: Can I divide a perennial hibiscus?  I did not allow enough room in the cottage garden and it is falling over on other flowering plants.

Answer: Hardy (perennial) hibiscus, Hibiscus moscheutos, commonly called rose mallow can be divided in early spring when new sprouts begin to grow. Simply dig around the base of the shrub and dig a little deeper than you think the roots may be growing. Remove the plant from the hole and place it on its side to pull apart sections of the root ball, making sure that each division has roots attached and intact. Keep the three or four sections moist and plant immediately at the same depth that they were planted originally.  Hardy hibiscus is different from tropical hibiscus which must be brought inside before temperatures drop below fifty degrees F. For now, try propping up your hibiscus with a perennial wire form made into a half circle which can be purchased at most hardware stores.       

Question: My chilopsis is covered with giant worms! The worms are yellow and black and green and black. How can I manage this invasion?

Answer: The larva or caterpillar is the Catalpa worm or "Catawba" worm hatched from eggs laid by the Catalpa Sphinx Moth. Just hatched caterpillars are white or pale yellow and turn yellow or lime green with black markings with age. All have a conspicuous black spine or horn on the back at the rear. The moth lays eggs on the underside of leaves of the catalpa tree, which is the only host plant or leaves that the caterpillar will eat. Your desert willow or Chilopsis linearis is in the family Bignoniceae which is the same as the catalpa tree. The caterpillars can defoliate the tree but will not usually cause tree decline. The caterpillars are loved by fisherman for fish bait and also, because of their large size, are readily seen by birds and consumed.  There could be up to three infestations a season, but usually do not pose a threat to tree vigor, but may look unsightly until leaves sprout again.
Question: The older leaves i.e. the ones on the bottom of my clematis vine are turning brown. It is in full sun and gets plenty of water. What could be causing this?
Answer: There is a clematis wilt or fungus, Ascochyta clematidina, but browning leaves are generally found on new growth and axil buds or end growth.  The stem dies back because it is attacked near the ground and the plant can't move water through its veins. Damp weather can increase the fungal activity, and the damage often seems to occur in early summer when the plant is growing vigorously. Leaves turning yellow and then brown at the base or on lower leaves sometimes occur in summer months when temperatures exceed 80 degrees F. Mulching with two to three inches of organic material and keeping water levels even can help the clematis vine to thrive. Fertilize clematis the same as roses, up to mid July with a liquid fertilizer.  Vine stems should still be soft and show green or "wick" (cambium should be green when vine is scratched with the fingernail).  Remove brown leaves, usually by crumbling away, and discard. If total stems are turning brown, prune back to the root zone and plants will generally recover on their own. Prevent the clematis from becoming completely dry between watering and keep the roots cool by applying mulch.  

Question: A friend said that the fall garden should be started in July, is that true with all this heat?
Answer: Many vegetables can be planted starting in mid July for the fall garden. Tomatoes are a good example. Some special precautions can be taken to insure that new transplants and vegetables started from seeds will survive the heat, drought and insects of summer. Many garden centers are offering vegetable transplants now for fall gardens. (See fact sheet HLA 6009)
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July Lawn and Garden Tips
  • A number of vegetables may be planted in July for a fall vegetable garden. This includes tomatoes, pepper, eggplant, squash, pumpkins, beans and corn. Click here for a complete fall veggie planting guide. (FS6009)
  • Tomatoes can be ripened in the house in hot weather. See below
  • During July and August, Bermuda lawns need at least 1 inch and fescue needs 2 inches of water per week. Each irrigation should soak the soil to 6 inches and is best if performed in the early morning.  Avoid frequent shallow watering.
  • Water garden and landscape plants deeply and early in the morning.  Most plants require 1 to 2 inches of water each week.
  • Lawns mowed high are better able to tolerate summers heat. Keeping mower blades sharp will produce clean cuts and grass will be less stressed and prone to disease.
  • Control Bermuda grass around trees with Glyphosate (Round-up).  Keep trees mulched, especially younger ones.  Mulch should look like a donut, not a volcano.
  • In July and August divide and replant crowded hybrid iris (bearded iris) after flowering is completed.
  • Spider mites love hot dry weather. These tiny pests attack many plants, especially tomatoes. Wash them off with jets of water and use horticultural oils and soaps, according to directions. A neem product would be a good choice for an oil preparation.
  • Watch for bag worms on your arborvitae and other pine trees.  Bt (Bacillus thuringiensis) is an environmentally effective spray.
Fall Webworms
You have probably noticed that the fall webworm appearance this year is earlier than usual. This suggests we will likely see very heavy loads of worms from now into the fall, especially in pecan trees. Their number each year depends on the presence of natural predators and the health of trees. Our spring rains contributed to an abundance of juicy leaves and this is probably the major factor in our current outbreak.

Webworms build their nests out at the ends of tree limbs and feed on the leaves within the web. Although the webs are unattractive, healthy trees usually survive and emerge the following spring with no evidence of damage. Pecan trees may be an exception to this statement. With very heavy infestations, pecans may produce fewer and smaller nuts. Smaller trees may be stunted due to the stress.
When webworms appear, there are several coping strategies available. This ranges from doing nothing, to physically removing webs in smaller trees, to a host of insecticidal sprays to prevent spread of the webs. Doing nothing is what most people choose to do.
If an insecticide spray is used, consider an environmentally friendly "biorational spray"-ones which are less toxic and more specific for the target pest. This would include products containing Bacillus thuringiensis (Bt), horticultural oil or spinosad.

Some conventional insecticides labeled for webworms contain acephate, carbaryl, permethrin and others. These are readily available.
All should be used strictly according to the label and will need to be applied with a sprayer capable of reaching the top of the tree and able to penetrate the webbing. This type of spraying may be best done by a professional. Remember, spraying will not get rid of webbing in your tree. Sprays are used only to prevent spread of the pests.
Click here for an excellent document from OSU with complete details of fall webworms.

Ripening Tomatoes in the Heat

If you want red tomatoes in the summer when the temperatures are typically in the 90s, you should harvest them and bring them indoors for ripening. Most tomatoes will not develop red color on the vine when the temperature is above 86 degrees.

The sunlight is not important when ripening tomatoes indoors. The temperature is important. They ripen best at 70 degrees.

Need more information?
Click on any of the links below
How to Take a Soil Test
How to collect a good sample of soil from your lawn or garden and get it tested at the OSU lab.
Trade names and where to find them   
How to Plant a Tree in Oklahoma Soil
Show and tell.
Landscaping and Gardening for Butterflies
How to attract butterflies to your garden 
Fescue Lawn Care
12-month maintenance calendar.
Bermuda Lawn Care
Ditto above.
Trees for Tulsa
A list of 50 recommended trees with descriptions.
Crape Myrtles
A list of over 100, by size and color.
Oklahoma Proven Plants
The new list for 2010.  State horticulturists, nurseries and growers pick their favorite plants, shrubs and trees.
Current and historical source of rainfall, air temperatures, soil temps and much more.  Click on Bixby station.
Fertilizing Vegetables
Handy chart telling you when and how much to fertilize various vegetables.