UNITED STATES—Cool season annuals were cool just a few months ago. Now, it is getting to be about time to warm up to warm season annuals. They will become a hot commodity as winter yields to spring. Many begin to bloom with warming spring weather and continue to bloom until autumn. Then, as the weather cools, they relinquish their space to cool season annuals.
Warm season annuals, or summer annuals (or warm season or summer bedding plants), are technically a bit early for a few regions. They should wait until after the last frost date, which might be later in the month for some climates. Even where frost is no threat, it may be too early to replace cool season annuals that continue to perform until spring weather.
Warm season annuals only seem to be seasonable now because the weather has been so pleasantly mild and even warm. Some cool season annuals are already beginning to deteriorate, which facilitates their replacement. Warm season annuals might dislike cool nights and short days, but should appreciate the opportunity to disperse their roots early.
Winter is technically not finished yet.
However, some degree of risk is associated with early planting of warm season annuals. Mild frost, although unlikely, is still possible in some climates, and could necessitate frost protection for vulnerable plants. Resumption of rainy and more typically wintry weather is more likely. Heavy rain can thrash fresh bloom. Sustained dampness can cause mildew.
Like warm season vegetable plants, warm season annuals can grow from seed or small plants from cell packs or little pots. Some prefer to grow directly from seed. Others prefer transplanting. Nasturtium, for example, prefer direct sowing. Petunia, which perform well after transplant as seedlings or small plants, are likely to languish if they grow from seed.
Because seed take a bit of time to germinate, they can go into the garden slightly prior to the last frost date. Similarly, they can start within a greenhouse early for later transplant. With proper scheduling, frost should no longer be a problem by the time seedlings emerge above the garden soil or are ready for transplant. More variety is obtainable as seed.
Without becoming invasive, common alyssum, Lobularia maritima, can almost naturalize in favorable situations. It disperses seed profusely, so often appears where it is an asset to the garden. Since it is so docile, it subordinates to more vigorous plants that it mingles with. It does well on loosely set stone walls. If necessary, it is easy to remove or relocate.
Common alyssum blooms with tiny but profuse white flowers. If they naturalize, varieties with pink or purple bloom eventually revert to white bloom after a few generations. Some varieties revert slower than others. Although popular as a warm season annual, alyssum can continue to bloom through next winter. Individual plants may survive for a few years.
Mature alyssum plants might get a bit higher than half a foot, but will get no higher than a foot. If they perform for more than a year, their progeny may begin to replace them before they get shabby. After removal, shabby plants, with a bit of shaking over bare spots, may share their last seed. Alyssum grows easily from seed and is available in cell packs too.
Horticulturist Tony Tomeo can be contacted at tonytomeo.com.