This article was written by Dale Martens for the 4th Quarter 2013 issue of Gesneriads of the Gesneriad Society. Dale and the Gesneriad Society has graciously given their permission to allow for the publication of this article here on the StrepbyStrep group. Thank you Dale and Peter Shalit of the Gesneriad Society!
Back to Basics: Streptocarpus
I can’t think of a more exciting genus right now than Streptocarpus. There are all sorts of species seed in the Seed Fund, plus there are plenty of fascinating new hybrids being created. Streptocarpus come in quite a range of sizes and flower colors and some have scent. Most hybrids bloom constantly and are happy growing in natural window light, under shady trees in warm weather, in greenhouses, or on plant stands. I’m in the midst of writing a booklet on Streptocarpus for The Gesneriad Society, so I know there’s a vast amount of information that can only be touched upon lightly in this article.
Culture: Most Streptocarpus plants grow easily in well-drained soil that’s allowed to slightly dry out between watering. Although that seems what’s best for them, some of us grow them on wick reservoirs and the roots are never dry. Discussions with some streptocarpus growers have resulted in agreement that 1/8 teaspoon of a balanced fertilizer or a fertilizer with slightly higher nitrogen is best. For at least three years now I’ve used a couple different non-urea, orchid fertilizers with higher nitrogen and never used a “high bloom” or higher Phosphate fertilizer. One of my Streptocarpus entries, ‘Heartland’s Peacock’ got the “Best Streptocarpus” award at the AVSA convention in 2012 and was in spectacular bloom. African violet growers often express concern that higher Nitrogen fertilizers will cause decreased variegation, but my variegated Streps do well with the higher nitrogen fertilizer. I grow under T-8 and T-12, cheap cool white fluorescent tube lights on for 10 hours a day. The Streps appear to bloom better under two sets (4 tubes per shelf) of T-8 light.
Let’s talk leaching as I believe it’s one of the most important Culture requirements. When you are growing plants in small pots (2-1/2 inch or 3-ounce plastic cups) and it’s time for them to go into larger pots, the plants have absorbed a few months of fertilizer. Therefore, leach out the fertilizer salts from the old soil before transplanting. Even if you like to remove some soil from the roots, there still is old soil attached. Leach by placing a pot over a bucket and pour slowly up to two cups of water through the pot. Often after leaching, I will then pour through the pot a light fertilizer such as a “Foliage-Pro” 9-3-6 which was mixed 1/8 teaspoon per gallon of water. An option for those who feel the plant’s leaves are too yellowish is to leach first, and then pour through the pot water that has Epsom salts mixed, 1 teaspoon per half gallon. Do not combine the Epsom salts with fertilizer. I’ve seen Epsom salts help center leaves become greener, but older leaves remain yellowish and should be removed. I leach my pots, no matter what size, at least every 8 to 12 weeks.
Soilless mix: Loose, well-draining soilless mix begins with sphagnum peat moss and to that most add perlite and vermiculite plus some dolomitic lime to balance the acidity of the sphagnum peat moss. The pH should be slightly on the acidic side. I have heard of some who like to add pasteurized leaf mold and others who add aged horse manure. Because we all have different water (rain, tap, reverse osmosis, well water), we have to experiment to see what soilless mix works best in the conditions our Streps are watered (reservoir or hand watering). I wick water, therefore my soil is lightened by as much as 50% with perlite. If you purchase soil, be sure to note if the package says “moisture retaining” as that possibly means a product was added that holds moisture. In that case the soil would need additional perlite. Also note if the package contains fertilizer. If so, then either don’t use additional fertilizer for the first month (particularly on young plants), or reduce the amount of additional fertilizer you use.
Insects: Hanging several yellow or blue sticky cards from the plant stands helps you see the type and quantity of flying insects, but I’ve also laid the cards down flat on stands to see if anything is walking around. I put one under a recently purchased Strep, and I caught mealybugs that had dropped off the plant. You can purchase insecticides for mealybugs, but I’d rather take a leaf and start over. The big fat, cottony mealybugs above the soil that hide in nodes and lay eggs on the backs of leaves are really a challenge. They move quickly, too, and you need to research as to what the various life stages look like. You think they’re gone, but that little, pale wiggly thing crawling on a leaf might be one of the stages. Again, it’s just easier to start over with a leaf, but don’t trust there weren’t eggs or larvae on the leaf cuttings. Mealybugs in soil are a challenge to kill, and if you have plants on reservoirs, you’ll see them floating on the water. I’ve had thrips that puncture and then suck on flowers as well as leaves. On flowers look for black dots on petals or pollen spilled in the flower’s throat area. It’s a good idea to keep the flowers and buds removed for at least three months. On leaves look for silvery lines because the top leaf layer was stripped. Thrips appreciate heat for their life cycle, so summer time seems when they do their best to increase population. Whatever critters you are battling, talk to your friendly gesneriad commercial grower and ask what’s best to use and follow the directions on the bottle. Mite damage seems to be near the tips of the Strep leaves rather than in the center. The leaves appear grayish due to the webbing. A strong magnifying glass will help you see the mites with eight legs walking on the leaves, especially if you use a very bright light because they run away from the light. If you use a Miticide, read the instructions and good luck. I never keep a mite infested plant. After treating plants for any insects, isolation for three months is the best thing one can do if you had insects of any kind. Unfortunately with mites, the three month isolation especially in a humid terrarium environment seems to just hold down the population. Once the plant is out in room air, the mites thrive and spread.
Propagation: A long time ago I used to remove the mid-rib and plant leaf halves in a light mix. It can work, but then I hybridized variegated Streps and those aren’t so cooperative and rotted due to the white areas. So I went back to cutting 2-1/2 inch sections from base to tip and do the slicing in a casserole dish so the leaves are under water. I leave them in the water for about 5 minutes. I bury each leaf section about ¾ of an inch deep in a soilless mix lightened with extra perlite and vermiculite. In the warmer seasons you’ll see young, green leaf tips popping out of the soil in a matter of weeks. In the colder seasons, it can take longer.
When you have a plant that’s overgrown, it’s time to separate the plant. First remove all the flower stems so you can see what you’re doing. Then remove all the leaves that are yellowish. Then look for natural separation areas between plants in the pot. Cut straight down with a sharp knife. I usually remove the bottom half of the soil under the newly sectioned plants. Then I repot into the smallest pot possible and place several of the newly potted plants in a gallon sized baggie, but don’t zip the baggie closed. The plants will go into shock and the baggies help keep humidity high and will support the leaves for the two or three weeks adjustment time. Keep the soil moist, but not soaking wet. The worst thing you can do for a Strep when repotting is to bury it too deeply in the pot. The newly emerging leaves will have a blackish-wet look.
Hybridizing: I have to thank Michael Kartuz who taught me about hybridizing Streps back in the 1980’s. He’d lecture to our Grow and Study Gesneriad chapter once a year and bring a carload of gesneriads including his Strep hybrids. After the club’s meeting was over, Michael kindly and patiently answered my hybridizing questions and gave me advice as to what to cross. When you hybridize, have a goal in mind and choose the parents accordingly. I wait until flowers have been open at least a week before pollinating. After fertilization, the pistil elongates and takes about eight weeks to ripen the seeds. One can get a first flower within 4-1/2 months from sowing seed, but only if seedlings are transplanted often. I begin transplanting when the seedling is 10 days old because transplanting stimulates growth.
The challenge in hybridizing is that your goal may need a couple of generations to achieve. Novices tend to want to name too many seedlings. They see every little difference, but the public doesn’t see the differences and wonders why the hybridizer named all those look-alikes. Novices need to check photos on the internet and compare their hybrids to ones already named. I throw away several hundred hybrids each year and name very few. My reputation means everything to me. Judges who judge the New Hybrids/Cultivars are to ask themselves, “Will I remember this hybrid in two weeks?” Therefore, I look at my hybrid and ask myself if that seedling was on a show table with 20 other show plants, would the judges remember mine two weeks later? Please don’t hesitate to contact me for advice on hybridizing Streps.