Well, there went what was supposed to be summer. It was miserably gray and cool, and there are plenty of plants quite confused at this point. I’ve seen maples and liquidambars with leaves of red (and still many of green), the tropical water lily leaves are half-size (although the plants are still valiantly making flowers), and there are agapanthus blossoms still hanging in there (they should have been done two months ago!). Maybe fall will be sunny, even warm; who can say in a year like this? Looking ahead to another season, it is time to build a good basis for next year’s growth, and that means soil.
Besides turning under any plants that have fulfilled their ornamental or nutritional roles for the last season, it is an excellent time to add additional organic matter. The breakdown of plant parts is the basis of good soil fertility and the health of the complex web of organisms that inhabit it. In nature, leaves, twigs, flowers, fruits, even whole trees and shrubs fall to the ground when their seasons are over. They have captured energy from the sun and used it to convert gaseous carbon dioxide and liquid water into cellulose and simpler carbohydrates. They have also taken nutrients such as nitrogen, phosphorus, and potassium from the soil along with other trace-mineral necessities like manganese and iron to complete their life cycle.
All these essential elements can and will be returned to the soil through the actions of myriad “lower” organisms. The amazing reward for plants (and us) from these lowly inhabitants is that they don’t use it all for themselves; they take a little and leave a lot behind. As they recycle the organic bits that once were part of a rose or a redwood, they make the elements available again to a new generation of plants.
If the detritus from your fall cleanup is too coarse or too voluminous to just till it under, this is a great time to make compost. As you clean up the old leaves of irises, agapanthus, and gladioli and deadhead roses, alstroemerias, and hydrangeas, put this harvest to work for you. As the runner beans and cucumbers give up their final crop, their vines will contribute their carbon and nitrogen stores to the compost bin and feed the myriad of decomposers.
Through their actions, these tiny creatures chemically alter the nitrogen and other nutrients once locked up in plant tissues and make them available again to plants. The cast of characters is large; from multitudes of microscopic bacteria to mysterious fungi with networks of hyphae that can pervade the entire compost bin from one initial spore. There are insects whose mandibles physically break down the fibrous tissue and earthworms that engorge the whole lot and disgorge it again in a supremely refined form, the “gold” in the dross.
Each is, of course, an opportunist, with a tiny agenda of its own. They already exist in the air, on surfaces of soil and roots of plants we gather, hiding in the corners that we didn’t reach with our rakes and brooms, so there is no need to capture and tame them. Assemble the pile of ingredients and they will move right in to colonize and capitalize on the bounty. Your reward is the compost. It is rich in soluble forms of nitrogen, myriads of fungi that can form beneficial relationships with plant roots, and other beneficial organisms, such as bacteria and nematodes, whichdefend against pathogens and pests.
Once you have worked the soil in anticipation of new plants, incorporating compost and other organics, it is time to plant. All that luscious organic matter will work to maintain moisture levels at root level; but, to further stave off the drying effects of potential warm days and dry Santa Ana winds, add an additional level of protection by adding a generous layer of organic mulch. In addition to retaining moisture, mulch will also attract many other microorganisms eager to attack and use this additional source of nutrition. They, too, use but little and leave behind a ready and more accessible source of plant nutrition. Consistently maintained mulch will contribute more than enough nutrients to your plants. Mulching combined with additions of compost when preparing soil for planting can ensure continued soil health. And healthy soil means healthy plants that are able to resist disease and pest outbreaks.