Tuesday, October 28

The Jekyll and Hyde of soils

Understanding and improving clay

Clay constitutes some of northern Illinois’ most fertile soils. That’s because the particles that make up clay soil are actually negatively charged, attracting and holding positively charged particles like calcium, potassium and magnesium. But clay also has its downside. It’s slow draining, slow to warm in the spring, and turns rock-hard when dry.

Many a garden failure is directly related to an abundance of clay in the soil. If your home-site soil is predominately clay, you and your plants will be forced to cope with its ill effects. Fortunately, however, there is one element that is the cure-all for such ills.

Organic matter is the fundamental stuff of the natural gardener. It is made up of dead or decomposing plant material. The more refined this source, the more readily it improves the quality of clay soil.

“Humus” is used to describe compost and other decomposed forms of organic matter that you can add to improve clay. It’s also the vital food for the microorganisms already in the soil. Feed these microbes and they multiply to improve soil quality and increase the overall health of your plants.

Adding humus to clay is the universal solution. Mix it into those tightly compacted soil particles and it holds them apart. Once separated, water passes through and roots travel more freely in search of moisture and nutrients. However, the humus you add one year can disappear by the next because the microbes literally consume it. So adding humus every year is essential to success with clay soils.

Finding byproducts

The combination of fertile clay and an abundance of humus can yield some of the most fertile garden soil on earth, and you will be amazed at the vigor of your plants. They’ll grow larger, flower and fruit more prolifically, and their symbiotic relationships with soil microbes will actually help them resist pests and disease.

The two best sources of quality humus can be found bagged for sale in home-improvement stores and garden centers. Compost, similar to that made in backyard bins, offers excellent light organic matter. Steer manure is composted to reduce the number of viable weed seeds that pass through the animal. This is a superior source of microorganisms as well as nitrogen and fine organic matter. When compost and manure are used together, you get the optimal combination for improving clay soil to produce rich harvests.

A more long-term approach to increasing drainage and loosening up heavy clay soil is to add organic matter that has not yet really begun to decompose. It will not be consumed by the clay in one season and remains far longer to improve plant performance.

Byproducts of tree trimming, lumber mills, stables and factories are cheap and plentiful sources. In the past, redwood soil amendments utilized the decomposition resistance of natural redwood to keep soils open longer. The best choice for your garden is whatever is most available in large quantities at minimal cost.

With such woody organic matter, the microbes work furiously to render it more usable, which requires more energy in the form of soil nitrogen. They’ll rob the surrounding soil of this nutrient in the process unless you apply supplemental nitrogen fertilizer to compensate for the imbalance. If you fail to add manure, fish emulsion or any other nitrogen-rich source, your plants won’t thrive.

No home site has perfect soil. Fortunately, you can change the quality of your soil with organic matter. So feed your clay well and often. In turn, it will feed your entire family for a long time.

Adding amendments in the fall

Adding organic matter, humus and manure to the soil in the fall gives them an entire winter and spring to become biologically active. The remnants of this year’s crop will have plenty of time to break down.

Organic soil amendments aren’t immediately valuable to plants. When you add them to the soil in spring, their benefits are delayed until everything “marries” and begins to interact and render their benefits to plants. It can take many weeks, even months, before the soil functions at peak levels. But if you prepare your soil in the fall while the earth is still warm and workable, you’ll be that far ahead and won’t have to touch the soil until just days before you’re ready to plant your first seed or seedling.

Begin by spreading amendments evenly over the area before you till or turn it. You’ll need a lot of manure and or compost to feed microorganisms and help the soil remain open and well-drained. Then boost fertility with materials such as bone meal for nitrogen and rock phosphate for phosphorous. An easy way to achieve this is to buy a complete organic fertilizer in pellet or granular form, which is easy to transport and apply.

Fall tilling is about opening up the soil to incorporate amendments, relieve compaction, increase oxygen and improve drainage. The deeper you get the better. Because you’re not planting right afterward, it’s best to rough till once in each direction. This leaves the surface irregular with large chunks of earth. The clods will gradually erode over the course of the winter, carrying amendments deeper down with the runoff. You can litter the entire surface with a mulch of shredded leaves, hay or straw to prevent erosion. The ground will flatten out considerably by spring when you’ll only need to fine till to prepare for planting.

Come spring, you’ll be pleasantly surprised at how much easier it will be to put the garden in without all that hauling, spreading and tilling. And best of all it will be in top biological form.

Maureen Gilmer is a horticulturist and former host of “Weekend Gardening” on DIY Network.