The outdoor gardening season may be winding down, but questions about growing plants are always in season. Michigan State University Extension specialists answer timely questions about landscape ornamentals, vegetable gardening, familiar insects and related topics.
Q. In a stand of goldenrod stems I noticed quite a few that looked as if they’d grown around a marble. What causes this?
A. The marble is actually a plant gall – plant tissue that forms in response to injury by insects or mites, bacteria, viruses, nematodes, or chemical or mechanical irritants. In the case of the goldenrod stem, the gall formed when a tiny insect inserted its egg into the stem. Ice anglers have been known to harvest the larvae inside the galls for bait.
Q. I grew luffa sponge gourds for the first time this year. They’re maturing nicely, but I don’t know when to harvest them or what to do with them after that.
A. Allow the gourds to mature on the vine. After vines are killed by frost, soak the gourds in water until the outer covering and interior pith soften. Then rub the gourds together or use a brush to remove the soft tissue. What’s left is the luffa sponge. Wash the sponge several times in clear water and let it dry. It’s then ready for use.
Q. What does the banded woolly bear caterpillar turn into? I’m guessing it’s some kind of moth.
A. The woolly bear (or woolly worm) – black on the ends and rusty brown in the middle -- is frequently seen crossing roads in the fall. After over-wintering in the larval stage, it will pupate and turn into an Isabella tiger moth. The adult moth has a wingspan of 1.8 to 2.6 inches and ranges in color from dull yellow to orange with scattered small dark spots. The underwings may be white, yellowish or orange, and the head is small and the thorax (the body segment directly behind the head) is hairy.
Q. What is a dwarf conifer?
A. A dwarf conifer is a variation on a species of pine, hemlock, fir, spruce or other conifer that never attains the height of the original species. “Dwarf” is a relative term – a 15-foot plant may be a dwarf if the original parent species typically tops 60 feet, for instance. Dwarf conifers usually grow slowly. They may vary from the species in form and color as well as height.
Q. What sort of care do rhododendrons need to survive a northern winter?
A. Keep plants well-watered through the fall so that they enter winter with plenty of moisture in their tissues. Rhododendrons hold their foliage through the winter, so they continue to lose moisture even after the ground is frozen and their roots can no longer take up water to replace what is lost. Make sure plants are surrounded by several inches of an organic mulch such as ground bark, wood chips or pine needles. Spray with an antidesiccant to seal moisture inside the foliage and stems. Build a windbreak out of burlap fastened to wooden stakes placed around the plant to protect plants, especially those in exposed locations, against drying winter winds.