Horticulture Newsletter 2015, No. 22

Video of the Week:
Controlling Clover in Your Lawn

Flowers:
Sidedressing Annual Flowers

Modern annual flowers have been bred to flower early and over a long period of time. They are not as easily thrown off flowering by high nitrogen levels as vegetables are. As a matter of fact, providing nitrogen through the growing season (sidedressing) can help maintain an effective flower display for warm-season flowers.

Apply a high nitrogen sidedressing four to six weeks after flowers have been set out. Additional fertilizations every three to four weeks can be helpful during a rainy summer, or if flower beds are irrigated. Common sources of nitrogen-only fertilizers include nitrate of soda, urea, and ammonium sulfate. Blood meal is an organic fertilizer that contains primarily, but not exclusively, nitrogen. Use only one of the listed fertilizers and apply at the rate given below.

Nitrate of soda (16-0-0): Apply 1/3 pound (.75 cup) fertilizer per 100 square feet. 
Blood Meal (12-1.5-.6): Apply 7 ounces (7/8 cup) fertilizer per 100 square feet.
Urea (46-0-0): Apply 2 ounces (1/4 cup) fertilizer per 100 square feet.
Ammonium Sulfate (21-0-0): Apply 4 ounces (½ cup) fertilizer per 100 square feet.

If you cannot find the above materials, you can use a lawn fertilizer that is about 30 percent nitrogen (nitrogen is the first number in the set of three) and apply it at the rate of 3 ounces (3/8 cup) per 100 square feet. Do not use a fertilizer that contains a weed killer or weed preventer. (Ward Upham)

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Deadheading Flowers

Some plants will bloom more profusely if the old, spent flowers are removed, a process called deadheading. Annuals especially, focus their energy on seed production to insure that the species survives. If you remove old flowers, the energy normally used to produce seed is now available to produce more flowers. Perennials can also benefit by lengthening the blooming season. However, some gardeners enjoy the look of spent flowers of perennials such as sedum or purple coneflower. Also, the seed produced can be a good food source for birds.

Not all plants need to be deadheaded, including sedum 'Autumn Joy', melampodium, impatiens, most flowering vines, periwinkle (Catharanthus), and wishbone flower (Torenia).

Those that do increase bloom in response to deadheading include hardy geraniums, coreopsis, petunias, marigolds, snapdragons, begonias, roses, campanulas, blanket flowers, delphiniums, zinnias, sweet peas, salvia, scabiosa, annual heliotrope, geraniums (Pelargonium), and yarrow.

Deadheading is easily accomplished by removing spent flowers. With some plants, pinching between a thumb and finger can do this, but tough, wiry stems will require a scissors or pruning shears. (Ward Upham)

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Pinching Mums

Though some garden mums do not require pinching back, most varieties will benefit. Pinching is done by removing the top inch of growth by pinching it between your thumbnail and forefinger. Pinch to just above where a leaf is attached. Pinching encourages lateral buds to break and grow resulting in a shorter, sturdier and fuller plant. The first pinching is usually done when the mums reach six inches in height. A second pinching should be done when the new growth from the previous pinch reaches six to eight inches. Usually that is all we have time for because the last pinch should take place before July 15. Pinching later than that can delay flowering resulting in a shorter time of flowering before frost kills the blooms. (Ward Upham)

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Rust on Hollyhock

Watch for rust on hollyhock. This is the most common disease on hollyhock and can cause serious injury as leaves are progressively killed through the summer. Look for yellow spots on the surface of the leaves and orangish to brown pustules on the underside. Infections can also take place on stems and green flower parts.

The first line of defense is to remove all hollyhock stalks, leaves and other debris in the fall and destroy them. Remove any infected foliage you see now. Just be sure the foliage is dry so you don’t spread the disease. Continue to remove diseased leaves as soon as they show spots. Try using a fungicide such as sulfur or myclobutanil (Immunox or Immunox Plus) to protect healthy foliage. Note that sulfur may burn leaves if the air temperature is over 85 degrees within 24 hours of application. Follow label directions for timing and rate. (Ward Upham)

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Pests:
Iris Borers

Iris borers are the caterpillars of iris borer moths. While described as being drab tan moths, they really are exquisitely patterned and colored ---- at least if one really takes a close look.  People rarely see the moths because during their short flight period in fall, they fly at night when mating and depositing overwintering eggs primarily on leaves, and especially at the base of the iris stalks.

As current-season leaves develop, newly hatched caterpillars/larvae climb up on the new foliage and create tiny pinholes through which they enter leaves. By splitting leaves at those sites, larvae can be found.         

By late summer, caterpillars will measure up to 1½ -inches in length and leave the somewhat restricted confines of the leaf. They will bore into the iris rhizomes to complete their feeding phase, after which they leave the rhizome to enter the soil where they will pupate. This will bring us back full circle to the emergence and mating of moths in the fall and the subsequent deposition of overwintering eggs.

The consequences of iris borers are twofold: current-season foliage becomes discolored with tattering along leaf margins, and leaves dying. Also, the bases of the plants as well as their rhizomes become an oozing mushy smelly mess due to fecal contamination along with the action of bacterial soft rot organisms.

At this current point-in-time, plants can be inspected for leaves displaying the presence of iris borer caterpillars. Due to their current small size, they can be squashed by a person running their finger and thumb along the leaf. Or, that leaf may be cut off and disposed of. If larvae are allowed to continue feeding uninterrupted, the entire plant and possibly the rhizome can eventually be roughed out. This would need to be done before pupation in order to prevent the production of new moths/mating/egg production. (Bob Bauernfeind)

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Ladybird Beetles

Both the adults and the larvae of the ladybird beetle are beneficial and do not feed on plants but rather on other insects including aphids, mealybugs, whiteflies, scale insects and the eggs of various other insects. So if you see these insects, do not spray. The larval form looks like a very small alligator-shaped insect. Larvae are covered with spines, about 3/8-inch long, and black with orange markings. (Ward Upham)

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Miscellaneous:
After-Effects of Too Much Rain

Some areas of Kansas have had saturated or near-saturated soils for several weeks now.  Gardeners are likely to assume that watering won’t be needed for quite some time now as soil moisture levels are very high.  Actually, watering may be needed much sooner than you expect.  Excessive rain can drive oxygen out of the soil and literally drown roots.  Therefore, as we enter hotter, drier weather, the plants with damaged root systems may be very susceptible to a lack of water.  Don’t forget to check your plants for signs of wilting or leaf scorching and water as needed. 

If irrigation is called for, water deeply and infrequently.  Usually once per week is sufficient depending on the weather.  Soil should be moist but not waterlogged.   (Ward Upham)

Contributors: Bob Bauernfeind, Entomologist; Ward Upham, Extension Associate

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