by Scott Loosley
QI would appreciate your advice on how to grow catmint, or Nepeta mussinii, successfully in my garden. I have two outdoor cats and they love the stuff! I've planted it three different times and it always dies within a month or two after planting. I water regularly, say two to three times a week. Is that too much water? AYou are a dedicated cat owner. Most gardeners cringe when they see a cat rolling in their catmint. I'm sure your cats appreciate your efforts, but it sounds as though the same kindness you exhibit toward them is killing your Nepeta. Too much water may be the problem. Nepeta mussinii is a member of the mint family, Lamiaceae. It is frequently confused in the nursery trade with Nepeta x faassenii, but there is a difference. Both Nepeta are aromatic perennials that grow to about 12 inches tall and 18 inches wide. Their foliage is a soft gray with toothed leaves 1 1/2 inches long, giving rise to loose spikes of lavender blue flowers. It makes a nice border plant, informal hedge and companion plant with roses.
The difference between the two types relates to the potential for a repeat bloom. Nepeta x faassenii can be cut back to half its height after the first bloom and will re-bloom again in about six weeks. Nepeta mussinii will not repeat bloom as consistently. The other difference between the to species is that the hybrid Nepeta x faassenii (N. mussinii x N. nepetella) has sterile flowers and must be propagated vegetatively, while Nepeta mussinii will go to seed. I'm sure your cat won't be able to tell the difference.
The problem you are having probably relates to your soil and watering habits. Nepeta prefers a well-drained soil and is rather drought-tolerant. It also grows and blooms best in full sun. You might try amending your soil with organic matter and planting your next catmint a little high so that water doesn't collect around the crown of the plant. Now is an excellent time to plant so that your catmint will become established this winter and bloom next spring. You will want to reduce the frequency of watering next summer. Your cats will love you for it.
QA number of plants in my yard are looking quite sad. Their lower leaves are turning a silver-brown color and some are dropping off. It seems to be worse on my rhododendrons and viburnums. Is this an insect or fungus? What can I do to correct the problem.
AI am afraid you are a victim of thrips. Thrips are extremely small insects that feed openly on the leaves of various garden plants. They use their rasping-sucking mouth parts to break open cell walls and remove the plant juices from inside. With the chlorophyll gone, the leaves take on a silvery appearance. Heavy infestations will result in leaf drop. If you observe the underside of the leaves, numerous small black excrement spots, or fecal specks, cover the surface. While using a hand lens, search the underside for tiny sausage-shaped insects. Adults will be dark in color while juveniles are nearly translucent or pale yellow.
Control of thrips is difficult since they live on the underside of the foliage. Spraying the underside of the plant with a heavy stream of water frequently will discourage some feeding. If the thrips persist, applications of insecticidal soap or horticultural oil at the summer application rate may be necessary. Follow label directions carefully and remember to spray the underside of the foliage thoroughly.
The use of a parasitic wasp to control thrips has been used successfully in greenhouses where they can be contained within the structure, but landscape use is still considered experimental. The wasp Thripobius semiluteus is commercially available, but release rates for landscape plants have not been developed. The use of insecticidal soap followed by the release of the beneficial wasp at several hundred per small tree or shrub has been successful in experiments. The wasp lays its egg in the immature thrip, or nymph, and consumes its host before emerging in about two weeks. Parasitized nymphs turn black. A list of beneficial insect suppliers is available from your county Cooperative Extension office.
Good sanitation habits will help to reduce the potential for thrip infestations from season to season. Rake up and destroy infested leaves that are on the ground. Pruning to improve air circulation around plants is also helpful. With a little persistence, significant infestations can be reduced to tolerable levels.
Scott Loosley is the horticulturist at the Gamble Garden Center in Palo Alto. His column appears the third Friday of the month. Send questions to Loosley care of Palo Alto Weekly, P.O. Box 1610, Palo Alto, CA 94302.
Back up to the Table of Contents Page