UNITED STATES—Cool season (or winter) vegetables are now finishing their season. Some continue to produce later than others. Eventually though, they all succumb to warming spring weather. As they do so, they relinquish their space to warm season (or summer) vegetables. Many warm season vegetables want to start growing as soon as possible. Later phases must wait for space to become available.
Later phases are no problem. They actually prolong the season for plants that are productive for only a brief season. For example, if sown at the same time, corn seed germinates and grows into stalks that produce all their corn at the same time. If sown in small groups every two weeks or so, corn seed grows into groups of stalks that produce corn every two weeks or so. That is ‘phasing.’
Phasing is more common with the cool season vegetable plants. Most of them are true vegetables, rather than fruits that are classified as vegetables. Individual plants produce only once, and cannot produce again after harvest. Conversely, most warm season vegetables are actually fruits. (They contain seed.) Many of the plants that produce them continue to produce after harvest begins.
An extensive production season is an advantage.
For example, squash, pole bean and indeterminate tomato plants that start growing in spring can continue to produce until frost. (Determinate tomatoes and bush beans have shorter seasons, so they can benefit from phasing.) Cucumber vines can produce until frost, but might get shabby enough (from aridity) for replacement halfway through their season. Pepper and eggplant thrive in warmth.
The various greens and the various root vegetables, which are truly vegetative rather than fruiting vegetables, should grow in phases.
Seed for corn, bean, root vegetables and most greens should go directly into the garden. Seedlings do not transplant well, and are expensive in sufficient quantity. Romaine and head lettuces are exceptions that produce well from seedlings. Tomato, pepper, eggplant, cucumber and squash seedlings transplant easily. If only a few are required, they are not much more expensive than seed.
On the coast between Los Angeles and San Francisco, lettuce, Lactuca sativa, seems to grow throughout the year. None of it actually grows in every season. Some varieties merely produce late enough for varieties that produce earliest to replace them. Slightly farther inland, lettuce is really only a cool season vegetable of early spring and autumn. The last new plants should finish by May.
There are many varieties of lettuce. Some are more tolerant of warmth than others. They perform well both late in their early season, and early in their late season. Others are more tolerant of cool weather. They can start early in their early season, and continue late in their late season. No variety produces through the coldest part of winter. Warmth initiates bolting (bloom), which ruins flavor.
The three types of lettuce that are most popular here are leaf, head and romaine. Leaf lettuce is the most variable. It can be blotched, bronzed or reddish, with variably ruffly texture. Some types of leaf lettuce mature in about a month. Some of the more substantial varieties of head and romaine lettuce start early, and can take nearly four months to mature. They can get to a foot wide and tall.
Horticulturist Tony Tomeo can be contacted at tonytomeo.com.