The Dirt on Dirt

Summer will be winding down soon, but here, the long warm fall means that the growing season is still moving forward. And, it’s also a great time to build a good basis for next year’s growth by feeding the soil.

Some softer plants that have fulfilled their ornamental or nutritional roles can be simply turned into the planting bed. The breakdown of plant parts is the basis of good soil fertility and the health of the complex web of organisms that inhabit it. These plants 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 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 garden cleanup is too coarse or too voluminous to just till it under, this is a great time to make compost. Throw all those old leaves of irises, agapanthuses, and gladioli, plus the deadheaded roses, alstroemerias, and hydrangeas on the compost heap. As the runner beans, which have actually harvested some extra nitrogen from the environment, and cucumbers give up their final crop, their vines will contribute their carbon and nitrogen as well to feed the many 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. Tiny insect mandibles physically break down the fibrous tissue and earthworms swallow it whole leaving behind in a supremely refined form while fulfilling their own tiny agendas. Multitudes of microscopic bacteria and mysterious fungi with networks of hyphae that can pervade the entire compost bin from one initial spore already abound in the air, on surfaces of soil and roots of plants so is no need to capture and tame them individually. Assemble the pile of ingredients and they will move right in to colonize and capitalize on the bounty. The reward is the simply called compost, but it is rich in soluble forms of nitrogen, fungi that can form beneficial relationships with plant roots, and other beneficial organisms such as bacteria and nematodes that defend against pathogens and pests.

Compost can be added to soil at any time either in a planting hole or spread as a moisture-retaining mulch. Organic mulch will also attract many other microorganisms eager to attack and use this additional source of nutrition. Because these microorganisms use little and leave behind much, a consistently maintained layer of mulch will contribute more than enough nutrients to the garden. Mulching and adding compost when preparing soil for planting ensures continued soil health. And healthy soil means healthy plants that are able to resist disease and pest outbreaks.

August Tips

• Plant South African bulbs as soon as they appear in nurseries. Look for freesia, ixia, watsonia, species gladiolus, and sparaxis.

• Pick ripe fruits and vegetables. Most will come off with only a gentle tug. If it takes more, then they probably aren’t fully ripe.

• Fruit trees and even vines like wisteria may put out suckers that should be cut close to the trunk or pulled of to keep energy going into the main growth.

• In this dry year, deep water trees and shrubs. Professional arborists can help with soil probes designed to deliver water deeply.

• Keep removing all dry brush, old weeds, piles of clippings, or prunings that could fuel wildfire.