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After an epic heat wave, some cool breezy days and a hint of rain coming, people are turning with relief to fall.
If you’re new to this area from a colder climate, you’ll be happy to know we have two full gardening seasons in Northern California. Our summer gardens of flowers and vegetables keep producing into late October, weather permitting. Sometimes tomato and pepper plants keep ripening fruit into November. But with our relatively mild fall and winter temperatures, we plant a whole range of plants now for harvest and blossoms in winter and spring. We can now pivot from our summer gardens and start planting cool season vegetables and flowers.
Trees and shrubs
The drought and reduced irrigation had already taken its toll on many landscape shrubs and trees, so this unprecedented heat was simply the final blow for some larger woody plants.
Unfortunately, coast redwoods are dead and dying all over the Valley. Calleryana pears, birches, ash trees and others were weakened. I recently looked at an Italian alder (Alnus cordata) which had abruptly dropped over one quarter to half of its leaves a day or so after the heat wave, indicating severe root injury.
I used the term unprecedented because this heat wave set some serious records. Two days at about 115 degrees, nine days over 100 and very warm nights in the 80s nearly until sunrise? That’s not something we’ve seen before, especially not in September. So it is actually hard to predict what the impact will be on these weakened trees and blasted shrubs.
The best advice is to wait and see. Leaf drop will obviously weaken the trees and shrubs, but pruning may not be advisable yet. Watering them deeply at least once this month can make a big difference. Allow the surface soil to go somewhat dry between waterings. Take care to avoid light, frequent irrigations that keep the plants damp at their crown — that’s an invitation to crown rot (phytophthora), and we’re already seeing samples of plants injured by a combination of heat stress and crown/root infection. Drought stressed plants can recover, but infected shrubs and trees may not.
Deciduous trees may simply drop their leaves early and go dormant. Most will not resprout this late in the season. We won’t really know the extent of their injury until spring. Larger trees that are prematurely defoliating should be assessed by a tree service for safety.
Lawns look rough, to put it mildly, after the extraordinary temperatures during the first ten days of September.
If you want to rejuvenate your lawn, rake out the dead patches, wait until we are a bit further into fall weather, and overseed. If there’s a lot of dead grass and thatch, you may need to dethatch first. Scattering seeds just before a rainstorm is especially effective. Repeat the reseeding as needed, sometimes two or three times, until you achieve good density. I have had good results overseeding lawns all the way into December. Fescue grasses generally have better drought recovery than other types, although some of the new perennial ryegrass varieties are proving to be well adapted here.
Or, if you’re tired of putting hundreds of gallons of water a week on your lawn, consider reducing or replacing it. More informal plantings of ornamental and native grasses, combined with flowering plants and other ground covers, can make a yard that’s more interesting, better for wildlife and the environment, and still suitable for light foot traffic.
In your vegetable garden:
- It’s time to plant brassicas, leafy greens, root crops, and start preparing your garden for onions and their relatives.
- Brassicas are also called cole crops. These are the winter vegetables derived, by centuries of selection, from wild cabbage (Brassica oleracea): broccoli, cauliflower (including Romanesco), collards and kale. While you can seed any of these directly in the garden, most gardeners prefer to transplant our seedlings they’ve started or purchased. Some require an even longer head start, making them a little tricky in our region due to our late summer heat — we’re already late for planting Brussels sprouts.
- Leafy greens we plant now, and through the winter, include kale, but also lettuce, arugula and radicchio, and the leaves of beets and mustards. Root vegetables we plant in the fall include beets, carrots, radishes and turnips.
- Onions and their cousins are quite easy to grow here, but it’s early to start them. Garlic and shallot bulbs typically are available in October. The easiest and most effective way to plant onions is from bareroot plants, which are shipped out to garden centers here in the first week of November. Go ahead now and spread some compost out over the bed where you plan to put them and water it a bit. Onions grow best in loose soil in full sun.
- If you’re not going to plant winter vegetables, a cover crop can reduce weeds, increase soil organic material, and provide nitrogen for next summer’s vegetables and flowers. Plant fava beans and clover to increase nitrogen and draw pollinators and other beneficial insects. Annual ryegrass and oats grow vigorously and crowd out weeds, then provide straw when mowed in spring.
Plant flowers now!
September and October are ideal times to plant annuals that flower in winter and spring. Right now we can plant snapdragons, stock, sweet peas, pansies and violas, calendulas and wildflowers.
While you can start these from seed, you’ll find it easier and faster to purchase seedlings for t
Sweet peas are vines that scramble up onto a simple trellis or fence. Grown for their powerful fragrance and for cutting, they’re not fussy except that they don’t like hot weather at all. So we plant them in fall for winter and spring bloom. Watch for white-crowned sparrows! They can decimate your seedlings. You may need to cover the plants at first with mesh or cages. Courtesy photo
- For winter and spring flowers for cutting, it’s hard to beat snapdragons. If you’re into bouquets, look for the old-fashioned varieties. They start blooming later than newer hybrids, but give great long stems of flowers from February through April. Snapdragons attract swallowtail butterflies and hummingbirds.
- Stock and sweet peas are grown especially for their fragrance. Sweet peas need a small trellis or fence to climb on. The seedlings are very attractive to white-crowned sparrows, which can demolish whole plantings in a single flock’s visit, so be prepared to cover the young plants with mesh or even strawberry baskets for the first couple of weeks after you plant them.
- Calendulas are bright orange and yellow daisies that bloom all winter. They are very easy to grow and will reseed happily, blooming all through winter and spring. They are especially attractive to bees and butterflies.
- Some flowers are best planted from seed. It’s an ideal time right now to scatter seed for California poppies and other wildflowers. California poppy seeds should not be covered; the seeds need light to germinate. The seedlings should be in a sunny spot where they won’t get crowded by other plants or weeds.
Winter vegetables and flowers all do best in full sun. Water every day or so at first, especially if we’re having unusually warm or windy weather. By late October you should only need to water every few days, and once we’ve had an inch or so of rain the plants can fend for themselves. None of the plants I’ve mentioned are sensitive to frost; all will grow and bloom through winter and spring.