Q: Many years ago, I purchased a Kaffir Lily (Clivia miniata) at the Philadelphia Flower Show and it has special meaning to me. Recently, the bottom leaves are turning yellow. What is causing this and what should I do? Also, sometimes it does not bloom well. Is it true that they need a rest period?
Answer: It is normal for the older leaves to turn yellow and eventually shrivel as the plant ages. Prune off the affected leaves. The rest of the leaves should be green, strappy, and healthy. Yellowing of younger leaves can indicate overwatering: a more-serious symptom. The potting mixture should dry out slightly between waterings when it is actively growing and completely dry out during the rest period.
Clivias do need a dormant period to help with blooming. Starting in late fall or early winter, withhold water and fertilizer and move the plant to a cooler area where temperatures are in the 40–50° F range. Keep it there for about 6–8 weeks, then move it back to a sunny location and begin to water again. You will soon see some
new growth and a flower stalk. At this point, begin to fertilize it every two weeks with a water-soluble houseplant fertilizer at half-strength. They bloom best when pot bound. Repot your Clivia every three to five years in the spring, after the flowers fade, when necessary.
By Debra Ricigliano, Lead Horticulturalist, University of Maryland Extension Home and Garden Information Center. This article was published originally in the December 2019 issue of Washington Gardener magazine. Read more posts by Debra.
Have a plant or insect question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask an Expert.
Have you noticed the large webbed sacs in the trees along the sides of the road lately? They do prompt questions to the Home & Garden Information Center’sAsk an Expert service. Often they are referred to as bagworms which causes some confusion because bagworms are a different insect.
So what are webworms and bagworms? Will they cause damage to trees? Let’s take a look at them both.
Fall Webworms. Photo: Kelly Oten, North Carolina Forest Service, Bugwood.org
Fall webworm (Hyphantria cunea)
Fall webworms show up every year but their populations can vary in size. Often they are insignificant in number and not too noticeable, but every so often there is a large population. The sacs can be numerous and quite large, leading one to assume they will devour an entire tree’s worth of leaves.
Fall webworm (Hyphantria cunea). Photo: Milan Zubrik, Forest Research Institute – Slovakia, Bugwood.org
But, thankfully, beneficial insects such as parasitoids and predators such as birds, who love to eat the caterpillars, keep populations in check and spraying is not necessary. Granted, the webs are not pleasing to look at. If they are within reach they can be pruned out and destroyed.
Fall webworm facts
There are two generations each year. One is active in May and the second larger population is active starting in late summer into the fall. However, the sacs can be noticeable in the trees all winter.
They feed on over 100 species of trees. Preferred hosts include walnut, oak, hickory, willow, apple, and other fruit trees.
The adult is a ¾ inch-long moth, white or white with black spots.
After eggs hatch on a host tree, the caterpillars produce a fine web over the ends of branches. They feed only within the web.
Mature caterpillars are about an inch long with noticeable long, silky hairs. They come in two colors, the ones with black heads are yellowish-white and the red-headed ones are brown.
By far bagworms are the more destructive of these two insects and need to be managed. They have voracious appetites and devour the needles of evergreens– particularly arborvitaes, junipers, Leyland cypresses, and cedars. We hear the cries of desperate residents wanting to know if the dead areas on their trees will regrow. Unfortunately, that answer is no.
Bagworm damage. Photo: UME / Ask an Expert
Bagworm damage. Photo: UME / Ask an Expert
Bagworm facts
There is one generation per season.
In addition to conifers, they will feed on deciduous trees (ones that shed their leaves in the fall) such as sycamore, maple, locust, boxelder, and linden, but the damage is not as significant.
Eggs hatch in late May or early June. Caterpillars feed and create bags made from pieces of the plant they are feeding on. The bags enlarge as the caterpillars feed during the summer.
The caterpillars pupate in late summer. Adult male moths emerge and fly to female bags that contain wingless female moths, then mating occurs. Females can lay 200-1,000 eggs which overwinter in the female bag.
Bagworm damage on Arborvitae. The brown portion will not recover. Photo: University of Maryland Extension
Evergreen bagworm. Photo: Eric R. Day, Virginia Polytechnic Institute and State University, Bugwood.org
Controlling bagworms
Fall, winter, and spring: Remove and destroy bags containing overwintering eggs. Pinch them at the tip or use a small clipper to remove the ones you can reach from the tree. Do not drop them on the ground near the trees. Dispose of them in the trash.
Beginning in late May into early June. Begin to look for small caterpillars moving on the trees. As they feed, small bags will form. The best time to spray is when the caterpillars have just emerged and are small. Bacillus thuringiensis (Bt), an organic insecticide, will help to control the young caterpillars.
By mid-July the caterpillars will be too large for Bt to be effective. Look for a registered insecticide labeled for bagworms at a plant nursery or hardware store. Contact an arborist or landscaper to treat large trees or if the bags are located high up in the trees.
Young bagworms can be controlled with an organic insecticide, Bacillus thuringiensis (Bt). Photo: Chazz Hesselein, Alabama Cooperative Extension System, Bugwood.org
Other tent-making caterpillars
There are two more tent-making caterpillars that are sometimes mistakenly referred to as ‘bagworms’. They are eastern and forest tent caterpillars. Both are active in the spring and not in the summer or fall.
By Debra Ricigliano, Lead Horticulturalist, University of Maryland Extension Home and Garden Information Center
Hydrangea leaves damaged by a late spring freeze. Photo: D. Ricigliano
Professionals in the landscape and greenhouse industry, trained horticulturists, and Master Gardeners often use the term “abiotic disorder” when diagnosing a plant problem. To the layman, this can be very confusing. To add to the confusion, signs and symptoms you see on your plants can look very similar to the damage caused by insects and diseases.
Surprisingly enough, the vast majority of plant problems are not caused by insect pests or diseases. Typically, the first thought that comes to mind when a plant is looking “ill” is that some insect or fungus has attacked it without much thought that it could be something else.
Ground ivy or creeping Charlie (Glechoma hederacea). Photo by Betty Marose
The famous quotation about the certainties of life which we all know includes death and taxes should also mention weeds! They are sprouting up all over. Even the most meticulously tended landscapes are not immune.
Where to Begin?
The first step is identification. You need to know your opponent. Control is more attainable if you know whether it is a grassy or broadleaf weed. Is it an annual, perennial or biennial? When does it germinate? Fall, spring, or summer?
The winter doldrums have settled in and as we count down the days to spring, why not brighten up your interior spaces with houseplants? Blooming plants cheer up a room with pops of color. Popular as gifts, their big advantage over cut flowers is that they are longer-lasting. And sometimes, given proper care, they can even bloom again.
Easy Blooming Houseplants
Anthurium Photo: D. Ricigliano
Anthurium (Anthurium andraeanum) The striking long-lasting flowers of this houseplant provide the color while the dark green, leathery, arrow-shaped leaves are attractive on their own. Botanically speaking, the flowers consist of a hood-like spathe surrounding a twisted spadix. They come in shades of white, red, pink, and, occasionally, orange. Easy care anthuriums bloom in medium light locations. During active growth periods, keep the soil moist and fertilize with a standard houseplant fertilizer in spring and summer.
Poinsettias were introduced to the United States in the 1820’s from Mexico
Poinsettias are the quintessential holiday plant. They are considered by many to be an essential part of holiday decorating. With proper care, poinsettias can continue to thrive long after the holidays are past. Getting them to re-flower can be a tricky endeavor and requires commitment. There are two ways of thinking about this. There are those that consider the plants disposable after the holidays and those that are willing to nurture them for the long-term in hopes they will bloom again the following year.
There are so many houseplants from which to choose. How does one decide?
Become familiar with the light conditions inside your home. Light can be the determining factor as to what you can grow in your indoor environment. The first question to ask yourself before plant shopping is, “What type of light exposure would my plants receive?”
