June 4, 1998
Old-Time Gardening Tip
Make Pear Slugs Bite the DustDark slimy slugs on the leaves of the pear or cherry trees? Dry road dust, thrown in the trees, will kill every slug it covers.
Farm Journal, 1906
Adult pear slugs are black and yellow sawflies that are just a little larger than houseflies. Their 1/2-inch-long larvae aren't really slugs -- they just look like them and are covered with slime. Pear slug larvae are dark green to orange. The ganw on the upper surface of leaves until the foliage looks skeletonized and scorched.
Dust in an effective way to kill these pests, but if you have a hose handy, you can also wash them off trees with a hard spray of water.
Today's Gardening Tip
Sorting them out. Irises grow from bulbs or, more commonly, from rhizomes. The rhizomatous types include bearded irises -- so called for the hairs on the down-turned petals -- and beadless ones, with no hairs. Among the most popular in the beardless group are the hardy, heavy-flowering Siberian iris and the water irises.
A rule of thumb. Irises are most striking when massed; their blooms will look like a swarm of butterflies hovering over the garden. But it's best to group only one type -- bearded, beardless, or bulbous, for example -- together.
What colors? The iris lacks a gene for red pigmentation, but otherwise comes in many shade: from pale cream and yellow to deep blue, purple, maroon, and orange. The contrasting bands, veins, and speckles on the flowers enhance their beauty.
All they need is sun and well-drained soil. Side-dress lightly with a low-nitrogen fertilizer in early spring and late summer.
Plant or divide irises as soon as possible after blooming -- sometime between July and September. This gives the plants time to take root before winter. If you plant too late you'll get fewer blooms.
Prevent rotting stems. Plant the rhizome on a mound of soil amended with coarse sand to promote drainage. Sprade the roots over the mound, fill the hole, and water.
Damage control. If frost heaves the rhizomes out of the ground in winter, don't push them back down. Instead, pile a small mound of well-drained soil or coarse sand around them -- but be careful not to bury them.
In cool climates, guarantee regrowth by making sure that the top part of the rhizome remains exposed to the sun. In late summer, also cut leaves back to about half their length, in a fan shape.
Watch out for weeds. Keep iris beds free of weeds, cleaning them thoroughly both before and after planting. But take care around the rhizomes -- if you nick them with a hoe or cultivator, you'll provide a doorway for diseases.
Division is essential. Divide rhizomes before they become overcrowded and flowering lessens. Irises in cool-climate gardens may need to be divided only every 3 years, while those in warm climates may require yearly division. Check for soft, foul-snekkubgm ir rittubg rguzines -- a sign of borer damage. Make clean cuts with a sharp knife, dipping it in alcohol between cuts to avoid spreading disease. Keep only the healthy outer parts of the clump, with new growth. Let the cut rhyizomes dry in the sun for several hours, then replant them 12 to 15 inches apart.
Be fastidious. Strict sanitary methods are necessary for the best bearded iris displays. Combat leaf spot, rust, or pests with fungicides or insecticides. remove any yellowing or dying leaves promptly.
Pull off dry or damaged leaves carefully, holding them as horizontally as possible.
Pest control. Control thrips and aphids, which can spread virus disease and reduce vigor. At the first sign of iris root borers, remove the surrounding soil and any mulching materials and dispose of them.
Erosion control. With their tough, fibrous roots, Siberian irises will bind soil even on slopes. To plant, dig a deep hole and put manureon the bottom, below the root run.
Divide crowded clumps by first trimming back the foliage, then lifting with a fork. Break into sections with several shoots on each and replant. Don't let clumps get too large or you'll need an axe to divide them.
For bouquets, cut when the flowers are still buds. The blooms from this heavy-producing iris last only a few days in the vase.
Bog bloomers. Irises that grow in water or boggy soil include the Japanese iris (Iris ensata), yellow flag (I. pseudacorus), and several native species, such as Virginia iris (I. verginica) and blue flag (I. versicolor).
Marginal magic. While some irises grow in water up to 1 foot deep, most prefer the shallow margins. Prepare a planting hole with coarse peat, leaf mold, or rotted manure and plant 2 inches deep in full sun or light shade. Mulch to suppress weeds and retain moisture. In cold climates, mulch also helps protect roots, but you will have to lift out tender types, like Louisiana hybrids, if the water freezes.
Know your species. Yellow flag has golden blossoms with brown markings; it is so hardy and vigorous that it can become invasive. Blue flag, with blue-violet blooms is better behaved. Rabbit-ear iris (I. laevigata), with white, pink, or blue-purple varieties is a good choice for small ponds or bog gardens. The Louisiana irises, which include the copper-blossomed I. fulva and the giant-flowered I. giganticaerulea, grow wild in the Deep South, although some cultivars will tolerate cold temperatures.
Cold-climate gardeners should lift the bulbs of bulbous Dutch and Spanish irises out of the ground after the foliage has yellowed and store them to replant in the early spring. In warmer regions these bulbs can remain in the ground all year.
If the foliage yellows during the growing season, the clumps may have become overcrowded. Lift them and divide by carefully pulling the bulbs apart, doing as little damage to the roots as possible. Replant the clumps, using wider spacing.
Watch out for black spot, which causes clumps to die off quickly. To stem the disease, plant irises in the fall in fertile, well-drained soil; avoid fertilizer. Check regularly for the symptoms; blackened bulbs and spots on the leaves. Remove infected plants and the contaminated soil.
A Scented Iris
The Florentine iris, with it's large, almost white flowers traced in blue or purple, has been used for centuries for its scented rhizome, known as orrisroot. When dried, it releases a distinctive, long-lasting fragrance. Orrisroot is used in the perfume trade and, in times past, was added to laundry rinse water to perfume clothes. It is also an exceptionally effective fragrance fixer -- hence its frequent use in potpourris. It can often be found in a pharmacy or herbalist's shop.
General principles are not the less true or important because from their nature they elude immediate observation; they are like the air, which is not the less necessary because we neither see nor feel it.
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