When to Repot
As plants become pot bound, they will need shifting to larger quarters. This applies to such permanent plants as trees and shrubs, but not to annuals or temporary kinds. Though spring and fall are the best times to repot, it can be done any time if roots are not disturbed. Usually, the rule is to move a plant to a container of the next larger size. If a plant is in an eight- or nine-inch pot, shift to a ten-inch size. If it is already in a ten-inch size, supply a tub that is just an inch or two wider in diameter.
As a rule, tubbed trees and shrubs can stay in the same container for several years if fed regularly and if some soil is removed from the top annually and replaced with fresh mixture. Some actively growing plants may require moving to large containers every two years. On the whole, avoid overlarge containers since the soil will hold too much moisture for plants to absorb it quickly. Overpot-ting tends to promote a water-logged condition.
Winter care varies with climate and types of plants. Discard annual and temporary kinds and bring house plants indoors or to a greenhouse. Palms, gardenias, and camellias in the South and yews, arborvitae, and pieris in the North can be left outdoors. In some cases, they will require shifting to less exposed spots and may even need covering with burlap, plastic film, or evergreen branches to guard against windburn or sunscald. Spraying the tops of evergreens with plastic wax in the early winter will cut down on evaporation. Remember that container plants in the winter still need water, but if soil freezes hard, wait for periods of thaw.
Where temperature drops to zero and below, soil will freeze solidly and many hardy plants may be killed. This is due, not so much to cold, but to frozen soil, which does
not allow tops to draw moisture, though they are still constantly transpiring. In below-zero regions, hardy evergreens, arborvitae, Japanese yew, hemlock, pines, and Douglas fir, if planted in containers with sufficient soil, will survive winters out of doors.
Where temperatures drop only to twenty degrees above, the choice of plant material is greater, extending to pieris, rhododendrons, azaleas, false cypress, firs, English and Korean boxwoods, cherry laurel, leucothoe, mahonia, and climbing euonymus. English ivy, myrtle, and pachysan-dra are three low evergreens that are reliably hardy. For milder climates, with little or no freezing, the choice is almost limitless, including camellias, oleander, hibiscus, crotons, poinsettia, aucuba, pittosporum, nandina, podo-carpus, acacias, palms, bougainvillea, and ficus, not to mention many annuals.