Cool-weather crops are some of the most nutritionally dense crops that we can grow. When Sonoma County’s cool and rainy period arrives, there are less pests with which to deal and less irrigating that we need to do. So, we get delicious and nutritious food with less work. But to successfully grow cool-weather crops to consume in the fall including cold-hardy crops that will overwinter and continue producing in early spring, we need to get the timing right.
Our job as fall and winter food gardeners is to bring our cool-weather crops to maturity or near-maturity before the earlier of a) the first frost/freeze date in our microclimate or b) the last day in the year that we have at least ten hours of daylight.
- FIND YOUR AREA’S FROST/FREEZE DATE: The frost/freeze date is based on a 30-year NOAA data set. Master Gardeners have distilled the important frost/freeze information for you. Find the weather station nearest you, look for the 32 degree (freezing point) line and find the 50-percent probability date. This is the reference point used by seed companies and many gardening resources for cool-weather vegetable garden planning.
- FIND YOUR AREA’S PERIOD OF LESS THAN TEN HOURS DAYLIGHT: Crops need an adequate amount of daylight to grow. Once daylight decreases below ten hours, crops perceptively stop growing. This period is based on your area’s latitude. In Sonoma County, November 18 is the last day of the year with ten hours of sunlight. There will continue to be less than ten hours of sunlight until January 23. The intervening period is called the Persephone Period.
Many average first freeze dates (50-percent probability) provided by NOAA for Sonoma County weather stations fall after November 18. Therefore, a number of gardeners in the county use November 18 to subtract a variety’s days-to-maturity (DTM) in order to determine the last day they can plant a particular crop variety and bring it to maturity. Because we are growing cool-weather crops during a period of shortening and cooler days, we add 7-14 days to the DTM to account for slower growth during cool fall months.
Within the group of cool-weather crops are crops that are “semi-hardy” that can withstand light frost (about 36 degrees). Examples include lettuce, broccoli, radishes and peas. Other crops are considered “cold-hardy”—meaning that a hard freeze (28 degrees) typically won’t kill them, even if the weather damages the outermost structures of the plant. This includes cabbage, spinach, kale, cauliflower, kohlrabi, arugula, mustard greens, Brussels sprouts, Swiss chard, celery root, mâche, collard greens, endive, among others. These “cold-hardy” crops, if brought to at least near-maturity by November 18, will overwinter during a normal Sonoma County winter. We can lightly harvest during these winter months and, when January 23 rolls around, many cold-hardy crops will begin growing again for an early spring harvest. In addition, because Sonoma County soils very rarely freeze, many root crops such as carrots, turnips, scallions, Daikon radish and beets can be stored in the ground over the winter as long as the soil is well-draining.
For more information:
- Year-Round Food Gardening in Sonoma County
- Vegetable Planting Summary
- First and Last Frost Dates for Sonoma County
- Focus on Fall Vegetables
- Cool Season Vegetable Gardening
- The Late Fall and Winter Food Garden (good read for October)
- Food Gardening Articles for detailed information about individual crops.
In the Garden
Fall is the perfect time to grow cool season vegetables, including greens. This month we highlight Master Gardener Ellen Scarr’s new article on arugula, a cool season salad green that is easy to grow and can provide you with a delicious harvest throughout the fall and winter months.
Other articles that will help you “get your greens in the ground” this Fall are:
Food Garden Tips
October Food Garden Tasks and Tips
For what to grow this month, click here.
- If a fall/winter garden was not planted, plant a cover crop, such as fava beans or red clover, to add nitrogen and organic matter, to improve the soil tilth and water penetration, and to help mitigate disease issues related to crop rotation. For maximum nitrogen benefit, cut down the crop next year just as flower buds begin to form, leaving the roots in the soil. The tops can be simply chopped and dropped or put in your compost pile.
- Mulch perennial crops and any bare soil. Option: rake leaves into a pile, run the mower over them and use this as organic mulch; 3-4 inches are recommended to retain soil moisture even in the cooler fall when drought conditions persist. Mulch also reduces splash and, therefore, reduces the number of disease spores that might move from the soil to your fall and winter crops.
- If tomatoes are still in the garden, cut off their water to help ripen what is left. Pruning the growing tips of indeterminate tomatoes will encourage the plants to direct all of the sugars and energy to ripening the existing fruit before the first frost (on AVERAGE, mid-Nov to early-Dec in Sonoma County).
- As veggies fade, cut the plants off just below soil level to preserve the soil micro-biology on the roots. Toss any plants showing signs of pests or disease. The rest can go into the compost. If you are immediately replanting the bed, just add a 2” layer of compost and if you encounter the existing sub-surface root, just put each new plant-start to the side of it.
- Strawberries can be planted October through spring. UC has some new varieties which you may want to check out. They should be available at local nurseries. We recommend day-neutral (“everbearing”) varieties for Sonoma vs. short-day types, but, if planting short-day varieties, they should be planted now through February. Trim off all runners as they develop because they weaken the mother plant and reduce fruit size. See University of California guidance.
- Lightly fertilize cool-season vegetables in a fall/winter garden if compost or a slow-release fertilizer was not added earlier. Do not add nitrogen to root crops. Citrus: apply 1/2 lb of 5-2-1 mixed with 1 tablespoon of Epson salts and water well.
- Fruit Trees: apply 7-5-7 per bag instructions around drip line of trees and work in, being careful not to disturb roots.
- Despite the fertilizing schedule outlined above, reduce the amounts if the rainfall outlook suggests below normal precipitation as more vigorous plants require more water.
- Turn off your automatic watering system when rainy weather arrives. But, if a dry spell follows the first rain storm, don’t forget to turn it back on. A drip system is the most efficient way to deliver water to your veggie garden. If you didn’t install one this spring/summer, now is a good time to rectify this.
- Clean, sharpen and oil garden tools and store them in a dry space. Steel wool will remove rust build up (wear gloves); some gardeners use wax paper throughout the year to wipe cleaned and dried blades after use to prevent/reduce rust. Drain garden hoses and hang them in the garage during the rainy season.
- Click here for ongoing monthly tasks.