Houseplants -Winter 2008
by: Hilary Newell
It’s a love of nature that has had people bringing the outdoors inside for thousands of years. Drawings from ancient Egypt show plants growing in troughs and on pedestals, and ancient art excavated from the Greeks and Romans indicate that they brought plants inside too.
As Europeans ventured forth and explored Africa, Asia and the New World, they collected unusual, exotic species of plants and this practice continues today, but with a greater knowledge and appreciation of the environmental dangers involved in transporting plants into new environments.
Most plants collected at the time were tropical in origin, meaning that they came from the area between the Tropic of Cancer to the Tropic of Capricorn. Being tropical, these plants needed warmer temperatures and to be protected from frost, so glass houses and conservatories were created to hold exotic plants like citrus, palms, ferns, orchids and interesting climbing vines.
Transporting houseplants back to England from the New World posed some challenges. Temperatures on ships were difficult to maintain and sailors didn’t necessarily know how to care for plants. In 1833, Dr. Nathaniel Ward created a glass case in which to protect his ferns from the coal-polluted, sulfuric-acid-laden air of London. He used this case to ship British ferns and grasses to Australia and received some native Australian species in return. This precursor to the terrarium was called a Wardian Case and it proved to be invaluable to plant collectors worldwide. Terrariums are still very popular today.
Enabled by the Wardian Case and improved conditions in homes, growing houseplants became a common hobby during the Victorian era (1837-1901). Favorites of the time were abutilon (flowering maple), jasmine, fuchsias, citrus, heliotropes, palms and aspidistra or “cast iron plant,” so nicknamed for its ability to tolerate the fumes from gas-powered lights that killed many other plants, and lots of different varieties of ferns. So enthusiastic were Victorians in their love of nature, architecture of the time was even influenced by the plant-collecting hobby. Sun porches and recessed bay windows became fashionable in the home as they provided sunny, warm, humid places to enjoy potted plants.
Houseplants grew in popularity in America in the 1950s and 1960s. My grandmother had about 50 African violets, and was constantly rooting leaves so she could share new plants with her friends. Every windowsill was stuffed and they seemed to bloom all the time. I can’t quite figure out how they survived in our old farmhouse that had only newspapers for insulation and no central heat, the only source of warmth coming from the wood stove and whatever heat was given off from cooking.
Granted, the plants in the kitchen looked the best and she moved them from room to room, cycling them in and out of the comfort of the kitchen. They never had any diseases or insect problems and I surmise that it was because of her watering habits. The water she used for the violets was so hot it steamed and the plants were watered only from the bottoms. Capillary action assured that the plant got enough water and the leaves never, ever had water on them. Phytophtera, a common root disease, is a frequent killer of violets, but it’s possible that she killed those spores and any insect eggs in the soil with the hot water. Steamy water, however, isn’t necessary to keep the leaves from spotting. Five degrees above room temperature does just fine.
It is quite common to find tropical plants in homes today and they are being used more and more in the garden as well. There are a number of flowering tropical plants that are excellent winter bloomers and are interesting year-round.
Night blooming jasmine (Cestrum nocturnum) is a pretty easy-to-grow flowering plant. It loves a really sunny window (southern, eastern or western), but can take quite cool nighttime temperatures. Logee’s says that as long as it stays above 45 degrees Fahrenheit at night, it will be fine. Humidity over 50 percent is preferable, but they can tolerate lower levels with no harm. After the plants bloom, they should be pruned to keep their shape. Don’t be afraid of pruning. These plants are large and rapid growers and they can tolerate a hard pruning, that is removing up to 50 percent of the plant’s mass. They grow heavily during longer days, so it’s best to prune them in early spring. Cestrum nocturnum grows to two to three feet in a container and has heavenly-scented white to greenish blooms at night. They are moderate to heavy feeders, so fertilize at least every week. Logee’s suggests that if too many leaves turn yellow and fall off, increase fertilizer to twice a week (or every watering) until the plant gets green again. Cestrum is not a true jasmine, but is similar in culture to several true jasmines such as Jasminum polyanthum, Jasminum nitidum,Jasminum azoricum and Jasminum sambac Flora Plena, a double-flowered variety.Several types of Jasmine are available from garden centers and mail-order catalogs. Logee’s Greenhouses in Danielson, Connecticut is one of my favorite sources for lots of unusual and not-so-unusual plants. My copy of the catalog is dog-eared and torn from being carried around and read extensively.
Jasmines are susceptible to whiteflies, spider mites and aphids. Placing the whole plant under a cold-water shower once every couple of weeks helps keep the spider mite population down, and it physically removes adult aphids. If you have a whitefly infestation, control can be tricky, but perseverance is key. Rodale suggests one cup of rubbing alcohol mixed with half a tablespoon insecticidal soap in a quart of water and apply once, then again every four days for three rounds.
Horticultural fine oil is another invaluable tool for insect control on houseplants. Non-toxic and environmentally safe, its mode of action is to suffocate insects, not to poison them. Apply a fine mist to the affected plants, being sure to get the tops and the bottoms of the leaves as well as the stems. The plant should be out of direct sun and should be sprayed early in the day to allow enough time for the oil to dry. As with any plant-care product, it is important to follow the directions on the label, including spraying a small portion to test for phytotoxicity or burning of the foliage.
One of the challenges that most beginning indoor-plant enthusiasts face is how to water. Cestrum and Jasminum both like to dry some between watering. When the top of the soil is visually dry, thoroughly saturate the soil until water runs out the bottom of the pot. A large saucer is a good idea, but if there is still water in the saucer a few hours after watering, it should be dumped.
There is no magic answer to the question ”How much should I water?” The conditions in everyone’s homes are different and therefore watering requirements vary. Generally, these plants can take up a lot of water in low-humidity/high-temperature situations, but be careful to not over-water, as they can be killed with kindness. Jasmines are not susceptible to foliage or root diseases. There are at least 10 varieties of Jasmines that will make exceptional houseplants, some climbing and some being shrubby. Check out the descriptions in the catalogs to find one with a form that you will like in your home. They can also be put outside for the summer either in their container or planted directly in the ground in a site with about a half-day of sun.
Another favorite tropical houseplant is actually a highly-invasive species in places like Hawaii, Australia, French Polynesia and Guam. Thunbergia grandiflora, also known as Bengal clock vine or sky vine, is not likely to become an invasive species here, as it is only hardy in U.S. zones 9A-11. I first saw this plant at a friend’s house when it wasn’t blooming yet, but she was gushing with excitement because it had bloomed all winter the previous year. Later I saw it on a trellis over an outdoor café in central Florida. With long hanging clusters of three-inch sky-blue flowers, this striking plant rendered me speechless. It provided a comfortable, cool shade over the café and covered an area that measured about 40 by 60 feet. As a houseplant in the north, it will never perform like that, but when I see one, it takes me back to that café. You will want to either give it a structure to climb on, or plant it in a hanging basket where it can trail freely. Its broad, heart-shaped leaves are a soft dark green and are attractive whether the bell-shaped flowers are present or not. In the home it will want a sunny spot with at least four hours of bright direct light. Thunbergia is day-length sensitive, so it is the shortening days of fall that make it set bud for winter bloom here in the North. They should be fed every two weeks throughout the year and should dry thoroughly between waterings. It’s a good idea to take the whole plant to the sink or tub to water. It prefers to stay above 60 degrees Fahrenheit at night. If you have an area where your thunbergia is growing well, it may become too large for your indoor space. So, in the springtime, after it is done blooming, it should be sheared to keep it from taking over. Cutting it back heavily won’t have a negative impact. It can be pruned again in midsummer, but after that it should be left to start producing buds for winter blooms.
The growers at Logee’s say that spider mite is the greatest insect problem you will face with this plant. The infestations begin with small light spots the size of a pinprick on the leaf. Plants that have summered outside often come in with a resident population. Use the same recipe of rubbing alcohol, water and insecticidal soap and spray the entire plant in the cool part of the day, repeat in 15 minutes and then again in four days.
Several citrus plants are commonly available for use as houseplants. The enjoyment is two-fold when growing oranges, lemons and limes as not only do the blossoms smell delightful, you can also harvest the fruits. Calamondin oranges are arguably the most popular fruited houseplants and for good reason. The little oranges are tart and can be used for marmalade or other baking. You probably won’t get enough harvest at one time to make a batch of marmalade, but a very sensible person who knows her way around a kitchen once told me that she harvests the fruits as they mature, and pops them right into the freezer until she has enough to make her marmalade. Brilliant!
Most citrus plants prefer full sun, and either a southern or western exposure in your house. Again, nighttime temperature should stay above 60 degrees in order to keep healthy growth on the plant. At temperatures below 60, these plants will survive, but the results will not be satisfying. Humidity should stay above 50 percent, if possible.
Most sources suggest keeping citrus in a clay pot in order to keep the air exchange active in the root zone. Let the surface of the soil dry to the touch in between watering and then, water thoroughly until the water runs out the bottom of the pot. Citruses require less fertilization than either jasmine or thunbergia, so about half a teaspoon of soluble houseplant fertilizer per gallon every two weeks is acceptable.
Over-fertilizing citrus can cause problems, so less is more in this case. If you notice that your citrus is requiring water a lot more frequently, it’s probably time to repot. Don’t increase the pot size by more than two inches if you do decide it’s time. They actually prefer to be a little pot-bound.
If you are lucky enough to have a young Meyer lemon, Kaffir lime or Calamondin orange, be sure to prune it regularly to keep a bushy shape. This also keeps the stems strong, as the fruit can be heavy when it ripens. The blossoms are numerous when they come into flower and they will scent the entire room. The leaves, when crushed, are fragrant and can be left in areas where the fresh citrus scent might be appreciated.
These varieties are all consistent bloomers and reliable producers. Don’t despair if your lime or lemon drops some fruit after it begins to form. The plant will only keep as many fruits on it as it can support and those that remain will ripen better than if there are too many. Full-size grapefruit trees can make decent houseplants too, but be prepared – they will grow to six feet before they produce fruit. The fruits mentioned here all will top out at about three feet and continue to produce when pruned regularly.
Citrus are not highly susceptible to insects, but it you have other infected plants in the house, those bugs will probably migrate to the citrus. It’s important to use the most natural methods of insect eradication possible if you are planning on using that lemon in your iced tea, or making marmalade with those oranges. The rubbing alcohol/soap mixture is a good one, and horticultural oil is a safe method too. Regular cold showers for the whole plant are recommended. Keeping the temperature above 60 and watering only when necessary should keep root disease at bay.
Houseplants have come a long way since the Wardian Case came into existence. We are lucky these days to have hundreds to choose from and we can be reasonably assured that they will be successful given proper care in the home.
Some research says that plants produce oxygen or cleanse the air, but that alone isn’t enough of a reason for having plants in my home. Exotic foliage can soften the edges of a room and scented plants stimulate the senses when one walks into the home. But when your plants send out those little miracle buds that turn into sweet-smelling flowers and eventually into fruit, you can look forward to enjoying the fruit on the plant while it ripens and tasting it once it has fully matured.
Hilary Newell is the greenhouse production manager at Bartlett’s Farm and compiles “The Farm Dirt” each week.