The December vegetable garden
Winter arrives on Dec. 21, the shortest day of the year. But, there is never a shortage of things to do in the vegetable garden here in the Sonoma Valley, even in winter.
This month, perennials such as asparagus, artichokes, horseradish, and rhubarb can be planted. And December is the month to establish new strawberry beds. Our winters are mild enough that we can plant vegetable starts even in December. You can set out starts of beets, chard, broccoli, Brussels sprouts, carrots, leaf lettuce, leeks, green onions, parsley, radishes, rutabaga, spinach, and turnips in December.
Here’s a rundown on things you can do this month:
Dig and harvest root crops such as carrots, parsnips, and salsify. Because the ground does not freeze here in the Sonoma Valley, sunchokes, carrots, parsnips, rutabaga, turnips, and other root crops can spend the winter underground – until you are ready to bring them into the kitchen.
Brussels sprouts, cabbage, chard, collards, and kale harvested now will keep for weeks if stored in a cool shed or basement.
To enjoy spinach, winter lettuces, and spring cabbage all winter, cover the plants with a row cover or plastic tunnel or cloche. Bend the leaves of cauliflower over the curds to protect them from frost damage.
Seeds from open-pollinated plants – that is non-hybrid plants – can be saved from the garden for planting next year. If you still have tomatoes or peppers in the garden, separate the seeds, thoroughly dry them, then label and store them in a closed jar in a cool, dry place.
Near the end of December start seeds of cabbage and hardy lettuces indoors or in the garden under cloches. Be patient, crops grow slowly during short winter days. Tender vegetable seeds such as tomatoes, peppers, and eggplants that require 12 weeks or more indoors can be started at the end of January or in February.
Perennials like artichokes and rhubarb can be set out in the perennial section of the garden this month or next. Plant these crops at the edge of the garden where they can produce for several years without being disturbed. Other perennials include horseradish, sage, mint, and rosemary.
Cover herbs still in the garden such as marjoram and rosemary with cloches and insulate them with a covering of leaf mulch. Divide and transplant potted or bare-root perennial herbs.
Finish picking late apples. Plant bare-root fruit trees in December. Prune back newly planted apple trees immediately after planting, reducing side-shoots to about one-half. Insert tree stakes before planting and make sure newly planted trees are secure. Water new trees deeply and add a fresh layer of mulch after planting. If you are not planting until spring, heel in trees or store in a frost-free shed keeping the roots moist.
Prune established apple and pear trees. Do not winter-prune cherries, damsons, peaches, or plums. Prune out broken, dead, or diseased branches and crossing branches. Make sure tree stakes are held firmly in place. Apply dormant oil to control over-wintering pests and disease.
Clean up dropped fruit and leaves. Compost leaves and fruit not affected by pests or disease. Place mouse guards, tree wraps, hardware cloth or chicken wire around tree trunks to protect them from rodents, rabbits, and deer this winter.
Prune blackberries, raspberries, and other brambles after a hard frost. Pruning can continue until late winter. Cut blackberry and hybrid berry canes that fruited this year back to soil level; tie newly formed canes to supports. After pruning, apply a mulch of well-rotted manure or compost.
Prune grapes as soon as they are dormant; remove one third to one half of the old wood and thin out undergrowth. Prune old grapevines severely so that they flourish next season.
Mulch strawberries with chopped leaves. Select strawberry beds now and work in plenty of compost. You can start a new bed with the strongest runners from old strawberry plants. A strawberry bed should be good for three years; even so, start a new bed each year.
Clean up parts of the garden that are not being used. Place compost and leaf mulch on vacant part of the garden. Check windbreaks, mulches, and other winter protection before and after storms. Install burlap screens and add mulch if necessary. Water fruit trees and the vegetable garden if the weather stays dry.
Make sure tools have been cleaned, sharpened, and stored in a dry place. Coat the metal part of tools with a light oil to prevent rust. Wooden handles can be painted a bright color to make them easier to find. Store tomato, bean, and other poles under cover. Store hoses not being used. Check your outdoor storage sheds for leaks.
Move tender container plants indoors or into cold frames or under patio covers for winter. Shallow containers should be sheltered away from frost and freezing weather. Set containers up on low supports so that they drain freely. Check these plants regularly. Remove spent plants from containers and compost; clean containers and store for winter.
Turn the compost pile with a garden fork and add water to speed winter decomposition. You can build a compost pile of leaves with a pen of wire or boards as small as 3 or 4 feet across and 4 or 5 feet high. Place and pack leaves in your composter in layers 1 foot thick; add a few shovelfuls of aged cow or horse manure to each layer. Separate layers with 1 inch of garden soil. Keep the pile moist, not wet, and turn it every 2 or 3 months.
Turn under the last of the vegetable remains still in the garden. Test the soil. If acid, add a layer of lime. If lacking in nutrients, add ground phosphate rock, granite dust or greensand to the garden by broadcasting these rock powders over the soil. Newly broken ground can be left rough through the winter; rain and frost will work the rock powders into the soil. Now is a good time to incorporate compost and green manure into the soil. It will blend in with the soil over winter. Rotary till or spade the material into the garden soil and let sit on the rough surface until spring.
Don’t depend on winter rains to water the garden. Check the soil frequently to determine whether or not it needs more water.
Plan ahead. Update your garden records from this past season and review your garden design; begin preparing seed and plant orders for spring. Plan nursery orders for spring. Winter is a good time to review back issues of garden magazines and to design your garden and plan crop rotations and succession planting for the coming year. Give some thought to how much to plant this year; plan a continuous supply without waste.
Steve Albert is the author of The Kitchen Garden Grower’s Guide available at Amazon.com. He teaches in the landscape design program at the U.C. Berkeley Extension. He lives in Oakmont.