Q: I usually grow a few cosmos in a mixed flower garden. Last summer they didn't bloom much. The plants were as big as usual, but the leaves were sparse and the flowers were only occasional. Do you think that the unusual summer weather was the cause, or do I need to change something about the way I grow cosmos?
A: I think that your problem is quite different. My cosmos didn't bloom well either; I was still puzzling over the problem when I read an article by British seed expert Graham Rice. He thinks that the problem is widespread and is caused by small profit margins.
Cosmos seed isn't, as Rice puts it, "a high value crop." The result is that seed growers do not spend time assuring that only the best plants are saved for seed. This has been true for many years of the old standard series like Sensation, Versailles, Daydream, and Seashells. The problem was obvious in plant trials made last summer by the Royal Horticultural Society. Plants of old cosmos varieties were very tall, and their flowers were both few and late.
Graham Rice recommends solving the cosmos problem by growing some of the newer cultivars. A packet of seeds may cost more, or there may be fewer seeds in the packet. This means that the growers' profits will be higher. It becomes worth their time to select only the best plants as seed producers.
New cosmos varieties that should bloom well are the Apollo, Cupcake, and Hummingbird series. Also, he recommends the individual cultivars called "Rubenza" (dark red), "Capriola" (white with pink edges), and "Xanthos" (yellow). The Double Click series are also floriferous, but all the experimental plants produced some single flowers instead of all doubles. The Cosimo series were fairly good.
If you lose track of the specific names to grow, look for varieties described as "new." Although that often means flowers that have not been tested much and may be disappointing, in this case I intend to trust Graham Rice and grow some newer types of cosmos next summer.
These cosmos are all descended from the species with white, pink, or maroon flowers. The other cosmos species grown in gardens is the smaller orange and yellow flowered one. It is a perennial grown as an annual and has only a few varieties. There is also the chocolate cosmos, which is a tuberous perennial. It should be grown and overwintered as if it were a dahlia. None of the 30 other species of cosmos are garden flowers.
Q: Do you always start cuttings of plants in water and then transfer them to dirt?
A: Almost never. I might stick the bottom of a cutting into a glass of water while I am getting around to planting it, but that would be only a way station on the road.
A few plants can live happily in water for years. Ivy, Swedish ivy, and coleus are common house plants that fit in this group. Often I see them growing in water, and once in a while I try the system. I change back to a pot full of dirt before long, because I find a mass of algae-covered roots in water an unattractive sight.
If a plant is, sooner or later, going to live in dirt, I prefer to start it in dirt. It may be easier for me to grab a glass of water and stuff in a cutting, but it is harder for the cutting. Roots that grow in water are tender and succulent. Since they cannot adapt to being surrounded by dirt, they die when transplanted. New dirt-adapted roots must replace them. In other words, a cutting started in water and moved to potting soil must make roots twice before it can start growing normally. I opt for finding the pot and giving the plant potting soil the first time around.
In my opinion, good light and high humidity are the most important factors in rooting cuttings successfully. I try to place the new cutting where it will get the most light without direct sun. Since I cover most cuttings with a clear plastic bag, sunlight inside the bag would build temperatures high enough to boil the water in the plant tissues. However, a clear plastic or glass cover keeps humidity levels high. Until new roots grow, a cutting cannot take water from the potting soil; if it is surrounded by wet air, its leaves will survive until photosynthesis gets going again.
A few plants native to dry places are best left uncovered and set in direct sun. They include cacti and succulents, those desert dwellers, and tender geraniums. Those cuttings need frequent watering, sometimes every day. But they are hard to root inside a plastic bag; in high humidity they are susceptible to various molds and rots.
I make cuttings between three and six inches long, and I cut all the leaves off the bottom inch. When I push a cutting into potting soil, I bury the bottom, and buried leaves would rot underground. I also make sure that the buried part includes at least one place where a leaf had emerged from the stem. Some plants grow roots from the bottom edge of a cutting, but many will also grow roots where once a leaf grew. I like to give cuttings all possible places to start rooting themselves. And I start them in very small pots - usually two-inch ones.
Some plants root faster than others, and most plants root faster in spring and summer than in late fall and winter. Some barely pause; new leaves are visible in a week or so. Others may take two or three months to show new growth. As long as a cutting looks healthy, it probably is. Eventually it will grow. Give all cuttings plenty of time to make a new root system before repotting them. If the little pot is full of roots, the ball will hold together when transplanted; if there is empty dirt it will fall off, sometimes tearing off new roots in the fall.
Q: For years I have grown penstemon, mostly plants with blue flowers shaped like trumpets. The only problem I ever had was with too many seedlings, which I had to pull out. I bought some new penstemon with red and white flowers, but most of them didn't live through winter. Why?
A: Penstemon are North American natives, some from the northern plains but some from as far south as Mexico. Your blue-flowered ones are probably Penstemon strictus, widely available and tough as nails. Other hardy species are P. barbatus (red), P. digitalis (white or pink), and P. grandiflorus (white). However, many of the hybrids have southern parents. They do not like cold winters. If you want to grow fancier penstemon varieties, try "Husker Red" or "Elfin Pink." Stay away from varieties bred in warm climates. Take as a basic rule that the larger the flowers, the more tender the plant.