The Central Valley in California is fortunate to have two full growing seasons. An average combined total of 267 sunny and partly sunny days allows for nearly constant crop production. The summer season is a long one and it’s getting longer as the climate warms. In years past gardeners were able to plant up until the first week of May. Heat spikes and hot summer temperatures now arrive in mid-April and last until mid- or even late-October. As the summer season lengthens here the winter growing season shortens. Winters, especially during drought years, have been warmer.
In much of the continental U.S., cool-season planting begins in early spring when temperatures warm after a long, cold winter. Here in the Central Valley, gardeners begin planting seeds and transplants for cool-season flowers and vegetables in fall several weeks before the average arrival of the first frost. That date used to fall around Nov. 15, but has recently been arriving later, and in some years, there have been few if any frosts or freezes.
Central Valley home gardeners can successfully grow cool-season vegetables and flowers in a shorter winter season by making a few adjustments. The timing for planting seeds of cool-season flowers and vegetables directly into the garden soil has become problematic. An untimely heat spike in early October will kill small seedlings.
Seeds of cool-season annual flowers and vegetables for transplant should be started in September (rather than in August as in previous cooler years) to be ready for setting out in 6 to 8 weeks, in mid- to late-October. Nurseries and garden centers now begin stocking transplants of cool-season flowering annuals and vegetables in October rather than September as well. When choosing transplants, check labels for varieties with heat and drought tolerance as well as shorter ‘days to maturity.’ When calculating harvest time with ‘days to maturity,’ take into account that, during the coldest weeks in late December and early January, young plants might become semi-dormant with little or no growth, but will recover vigor as temperatures warm again.
Amend the soil in late September or early October by adding copious amounts of compost and humus and turning the soil to a depth of at least 8 inches. Root crops - including carrots, beets, turnips and radishes - will not develop properly in slow-draining heavy clay soil or fast-draining lightweight sandy soil. Allow the amended soil to settle for two weeks, then plant. Root crops, especially radishes, will also develop a bitter, hot taste when soil temperatures are too high. Leafy greens also turn bitter when temperatures are too high. If temperatures drop near freezing, which has usually occurred in late December and very early January, young plants will go into semi-dormancy with little or no new growth, but will recover vigor as temperatures warm again and be ready for harvest by February. Many cool-season crops, especially those in the brassicae family, tolerate cold temperatures very well. In fact, frost-kissed Brussel sprouts and broccoli are said to have a sweeter taste.
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Written by UC Master Gardener Elinor Teague