Fall planting is a California invention. True, in other places bulbs are what have always been planted in the autumn, but in this part of the country fall planting involves a lot more than bulbs.
Californians have discovered that in our mild climate just about anything can be started during this season. The exceptions are minor: Roses, deciduous fruit trees and a few other things that immediately lose their leaves are better planted in winter when they are dormant; subtropicals that might be damaged by frost, such as bougainvillea and banana, are best set in the ground as the weather warms in late spring. But in the fall, you can plant ground covers, cool-season grasses, shrubs, trees, perennials, annual flowers, cool-season vegetables and, of course, bulbs. In short, you can start an entire garden.
The reason that so much does so well when planted in the fall has come to light only recently. It's well known that warmer soil stimulates root growth and that cooler days put less stress on plants. But new research at Oklahoma State University, as reported in Organic Gardening magazine, indicates that a plant's first priority is to grow leaves, and then branches, and finally, in the fall, the roots get their turn. So it would seem that plants are programmed to grow roots in autumn.
What that means is that during the fall you'll notice little change in the garden (it's all occurring underground), but when spring arrives the leafy growth will be strong, even furious. Perhaps more important, the plants will be securely founded. Often when you plant in the spring, especially late in the season, you get lots of healthy foliage that then wilts or even dies in summer because there isn't an adequate root system to support it.
If these findings bear out, it also means that plants set down in the spring, despite that season's lovely weather, don't grow many roots until the following autumn. As a result of this research, fall planting is beginning to spread to other parts of the country. But it began here.
An equally good reason to plant in the fall is that it marks the beginning of the rainy season, when watering is not as much of a chore. Even if it doesn't rain heavily (though this year has all the signs of being a wet one), when the sun is lower in the sky and the days are shorter, watering is not as crucial.
Good gardeners will tell you that adequate water during the first year of growth is extremely important; you don't want to stress the plants at all. Here, too, new research, this time by the University of California, has provided an explanation. It turns out that, despite all the warnings one hears about over-watering, doing so is almost impossible during the first few months of a plant's life in the ground. The researchers found remarkably more roots on plants that were watered thoroughly and often at first than on those that were watered only when it seemed necessary. Of course, don't drown the plants, but never let them completely dry out either. For gardeners who plant in the fall, it's much easier to satisfy the initial thirst at this less stressful time, and any rain helps.
A word of caution is appropriate here: A frequent watering schedule applies only to new plants. Those that are established should be irrigated less often once the weather cools--even during Santa Ana conditions. These winds do not dry the soil as much as you might expect. When plants wilt temporarily, you can scratch at the soil surface and often find it still moist; the plants just can't accommodate the water fast enough. Over-watering in the fall can be fatal--just as it is in the summer--at least early in the season when the days are still warm or downright hot. Root rots thrive when the soil is warm and moist. As winter takes over, over-watering is not as much of a concern, because even though the soil is moist or soggy, the temperature is cool.
However, bulbs planted in the fall, especially ranunculuses, are extremely sensitive to over-watering until they have grown roots and sprouted through the soil. Many gardeners water their bulbs only once after planting--thoroughly--and then wait until they have sprouted before watering again. Some bulbs, including tulips and daffodils, may need to be watered a lot because they tend to sprout late, but never leave them in soggy soil. Let the soil dry before watering again.
There is one other reason that fall is a natural time to plant: That's when nature does it. Following the first rains, seeds germinate and everything starts to grow. Even weeds sprout. That is why California native plants must be planted now. The same holds true for all similar drought-tolerant plants from summer-dry, winter-wet Mediterranean climates, from eucalyptus to ice plant.
If you plant in the spring, or even during the winter, you'll have to water heavily in summer, while the plants are trying to take hold, and you'll run the risk of encouraging root rots. Drought-tolerant plants, especially California natives, are very sensitive to over-watering and can virtually die before your eyes.
The many advantages to using more of these non-thirsty plants in gardens are explained on the next few pages. Perhaps you'll be persuaded to grow things that need less water, but for the moment, remember that fall is the only time to plant them.