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Cool summer means a quiet end to season
By Tony Tomeo
The last summer of the millennium ends this week, though it may seem that many of the plants in your garden are waiting for it to begin. A lack of summer heat may leave some species which prefer heat looking rather drab. In my garden the bougainvillea, which typically refrain from blooming early in summer but end the season with a grand finale of extremely profuse, bright magenta blooms, are still waiting to get started. Some garden enthusiasts have experienced similar results with crape myrtle or trumpet vines.
Because many plants which prefer heat are also sensitive to cold, they are the same individuals recovering from last winter's frost damage. The new growth that replaces frost damage normally grows vigorously enough through summer that some of it will survive the following winter, even if a damaging freeze occurs again. New growth that is weak or in the early stages of development is more sensitive to cold. Although winter is still several months away, garden enthusiasts should be aware that frost protection will probably be an important concern at the beginning of the year 2000.
Bulbs will soon be made available and should be planted as soon as possible. Most nurseries market the various bulbs at the beginning of the season in which they should be planted. Summer bulbs are normally not planted until early November. However, spring bulbs may be planted now. The more common spring bulbs include daffodils, freesias, Dutch iris and crocus. Watsonia, scilla, sparaxis and tritonia are less common, but interesting alternatives. Grape hyacinth was almost too common for a long time and considered by some to be a weed, but it's still available in a few varieties. As much as I prefer to disagree with Martha Stewart, grape hyacinth is still one of my favorites for its reliable production of blue flowers.
From now until December, cool-season vegetables can also be planted. Beets, turnips, carrots, radishes, garlic, onions, leeks, broccoli, cauliflower, cabbage, collards, kale, kohlrabi, mustard greens, turnip greens, lettuce, chard, spinach, celery and peas are all choices for autumn and winter vegetable gardening. Garlic and onions can be planted from "onion sets," which are juvenile onions grown from seed last year and dug up and cleaned after they begin their dormancy cycle.
Many vegetables, such as broccoli, cauliflower, collards and cabbage, perform best if planted as seedlings either grown earlier in the season or purchased from a nursery. Vegetables which develop quickly and uniformly, such as radishes, lettuce and celery, should be planted in small groups every two weeks. If planted in this manner, they will provide a steady supply of vegetables through the season, rather than too many at the same time. Slower vegetables, such as broccoli, do not all develop at the same rate and may be planted at the same time. Root vegetables, such as beets and turnips, may be left in the ground or stored after reaching maturity, and so may also be planted in larger quantities. Peas are only planted once, early in autumn.
Cool-season annual flowers include pansy, viola, Iceland poppy, calendula and alyssum. These flowers are at their best in winter, but should be planted as the warm-weather annuals finish.
Tree of the Week: American Sweet Gum
I realize that it is somewhat early in the season, but I don't want anyone to miss the display of autumn color exhibited in the American sweet gum, Liquidambar styraciflua. Furthermore, autumn color is probably my favorite horticultural topic. Sweet gum is one of the more popular deciduous trees in the Santa Clara Valley and commonly used as a street tree. Aside from excellent autumn color, sweet gum trees are handsome in all seasons. During spring and summer, their well-foliated canopies are finely textured, similar to maples', but of a softer green. Their excellent upright conical form is conducive to grove planting and presents a pleasing silhouette in winter. Although they are very common in lawns and near pavement, surface roots and messy fruit (seed pods) are often problems. Therefore, sweet gum trees are best used in less refined areas of landscapes.
Trees in irrigated areas can lose large branches during warm, humid weather. (Heat stimulates vascular flow, and if humidity minimizes evaporation from foliar surfaces, weight gain may be more than the branches can support.) Branches which are not growing upright are usually more at risk of breaking. Sweet gum trees are sensitive to alkalinity and should not be planted where they may experience problems.
Although soil can be amended around young trees, it is nearly impossible to accommodate large root systems of mature trees, which express their distaste for alkalinity as chlorosis. Autumn color is best when cold weather arrives suddenly after a hot summer, which unfortunately implies that color this year will probably be less than extreme. Sweet gum trees are resistant to oak root rot fungus and will eventually grow to 60 feet tall and 20 feet wide.
Most older trees were grown from seed and express a small degree of genetic variability, and some may not color as well or may color later than neighboring trees. It is common for some ungrafted trees to begin coloring as others are already bare. Genetically identical modern cultivars perform uniformly. This is desirable in group plantings, but seedlings can sometimes be found for those who prefer a more natural appearance.
Horticulturist Tony Tomeo can be contacted at 358-2574.
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Willow Glen, California Since 1992
