April 2003 - Indiana Yard and Garden - Purdue Consumer Horticulture

April 2003

Q. My bearded iris looked big and healthy but barely bloomed. What could be wrong? — Melissa Eddy, Lafayette, Ind.

A. Several factors may contribute to a lack of iris flowers. The most surprising is that the rhizomes have to be exposed to sun. They should be planted horizontally, with only the lower half in the soil. It’s easiest to dig a hole and then create a ridge for the rhizome to lay on. Cover only the roots and sides.

Sometimes, iris are planted properly, but annual mulching ends up burying the rhizome. Make sure you clean it off as you tend to the plants through the garden season.

Bearded iris require full sun for peak bloom. Assess their location and move them to a sunnier site if necessary.

Divide iris every 3-5 years, or they’ll cease to bloom. In late summer, place a spade or fork under the clumps and lift them entirely. Use a sharp knife to separate the rhizomes so that each one has a green growing point coming from it. Be sure to leave as many roots on each rhizome as possible. Cut the leaves to one-third of the original height. Discard the old center divisions and any rhizomes that are soft or rotted. Plant the iris 18-24 inches apart.

Apply a low-nitrogen fertilizer, such as 5-10-10 or 5-10-5, in the early spring and just after flowering. Place the fertilizer around, not on, the rhizome, then water it thoroughly.

Q. My peonies are turning brown where the stalk meets the ground, causing the stems to fall down. Some of the leaves are wilted, and the buds never open. This has happened for years. I don’t see any insects. — Don Walker, Nashville, Ind.

A. Botrytis blight causes the symptoms you have described and can also cause a gray mold to form around the base of the stalk. Wind and insects carry the fungal spores.

Sanitary measures offer the most effective means of control. Start with a thorough cleanup of old, infected stems and leaves and other plant debris in the fall. This reduces the overwintering site for the fungus. Pull the soil away from the crown without injuring the buds.

In the spring, remove and destroy any wilted or rotted shoots as soon as you detect them. If mulch or another covering is used for winter protection, remove it in the spring before the new shoots emerge from the soil.

Improving air circulation and penetration of sunlight to peony plants often solves the problem. Sometimes, however, chemical control is necessary. If so, spray with a fungicide labeled for botrytis blight when new shoots appear in the spring. Follow label instructions. Thoroughly soak the surrounding soil. Repeat the procedure a week later and again when the shoots are 3-6 inches tall.

Q. It seems like annual plants, like Christmas decorations, are available earlier and earlier each year. Is it OK to buy them so early? — Linda Todias, Merrillville, Ind.

A. Researchers keep records on weather patterns and have developed maps that predict, on the average, when you may expect the last 32 F freeze of the spring and the first frost of the fall. At the time of your frost date, you have a 50 percent chance of a freeze. Planting before that date just means the odds are greater that the plants will suffer from a freeze.

You can protect a small number of plants with floating row covers, upside-down bushel baskets or other protection, but it isn’t wise to risk large, expensive plantings when the odds of a freeze are against you. You’re best off to wait until the chance of freezing drops.

Your frost-free date can be found by calling the Purdue Extension office in your county or by consulting “Effects of Cold Weather on Horticultural Plants in Indiana,” available online at http://www.agcom.purdue.edu/AgCom/Pubs/HO/HO-203.html.

Retailers count on us chomping at the bit for spring’s arrival. We, anxious for the end of winter, provide the demand so they, looking for increased sales, provide impatiens and petunias in early April. We’re best off to purchase cold-tolerant annuals like pansies or ornamental kale at that time of year!


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