Biennials: MANY BIENNIALS flower in early and midsummer, thus usefully filling an awkward gap that can occur between the spring and summer flowers. Like annuals, they are temporary plants which should be pulled up and put on the compost pile when they have finished flowering. Also, as with annuals, though it's easy enough to save seed of most kinds it is usually impossible to prevent cross-fertilization of different varieties, as a result of which home-saved seed produces only a mongrel population. The distinction between annuals, biennials and herbaceous perennials is not always clear-cut since sometimes varieties of one group can be treated as if they belonged to one of the other groups; hollyhocks (Alcea), for example, can be grown as annuals, biennials or short-lived perennials. However, to be sure of a regular succession of biennials it is necessary to sow seed every year at the correct season.
Plants are called annuals, biennials or per-nnials, according to the length of time the root jves, but the differences are not always absolute, .rid are often changed by cultivation. Perennials, >uch as quack grass and peony, often have thickened, tuberlike roots, in which nourishment is stored during the growing periods, to be drawn upon when the plant flowers. Biennials such as beets and carrots show similar development. |
