Now is a great time to pump up your soil so that your plants have a healthy foundation in which to grow.
No matter what type of soil you have — and nearly all of us in San Mateo County have various degrees of clay soil — it more than likely will benefit greatly by the addition of compost. Compost is organic material — leaves, grass clippings, kitchen scraps, straw and manure, for example — that has decomposed into soft, small pieces. By adding compost to your soil — no matter what type of soil you have — you make it more fertile and improve its structure. In the case of clay soil, compost loosens it up so that water drains well through it. Left to its own devices, most clay soil holds on to water too long, and air can’t get in. The roots of your plants, and all of the helpful organisms that live in soil, can’t survive without air.
By the way, clay soil isn’t "bad” soil. It may be clingy when it comes to holding on to water, but it also holds nutrients, unlike its sandy sibling who is temperamentally inclined to let water and nutrients wash right through.
While I’m at it, here is a plea to love the one you’re with. Yes, most every gardener pines for a loamy soil — one that is exceptionally well balanced in drainage and nutrients, and posts the perfect pH by being neither too acidic nor too alkaline. Certainly many of us are partnered with soil that is far from our dream date. And yes, with enough money and time — and in some cases, a backhoe — you can utterly transform your soil. But consider this: Why not understand, appreciate and work with what you have? Yes, make a few improvements — add some compost, for example — but plant the plants that have an affinity to the soil and conditions natural to the plot of earth on which you live.
Another plea: Do not add sand to clay soil. No, it does not help with drainage.
But I digress. Back to compost. How, and how much?
I picked the brains of fellow master gardener, Terry Lyngso, whose family operates Lyngso Garden Materials in Redwood City. Terry knows the dirt on dirt.
First, do not work wet soil. Wait until it is pretty dry. (That won’t be long, and it may be right now, given the lack of rain this winter). Tromping on and digging into wet clay soil only compacts it — squishing those pockets that could hold air.
Sheet mulching is a great technique. Here’s how to do it:
If weeds are emerging, knock them down or mow them. Then put a layer of cardboard, corrugated paper, or newspaper (only pages printed with black ink; none with color) on top. Overlap them so that you don’t leave openings for the sun to get through and encourage weeds to sprout. Pile about one-half inch of compost on top. Then add about three or four inches of mulch, such as small or medium-sized wood chips.
If you are trying to amend a bed that already has plants — say, an ornamental bed with perennials — use the same technique but do it in between and around the existing plants. If it makes more sense, forgo the cardboard or paper layer, and simply lay about one-half inch of compost around and between the plants. Add on top about two inches of mulch. In all cases, be careful not to place material next to where the plant emerges from the ground.
By late spring or early summer, you will be amazed at the transformation in your soil. Push aside the mulch, and chances are you will see a big difference in the soil; and signs of life, such as our buddies, the earthworms, wiggling in surprise at being uncovered (I tell you, two things that make me so happy in the garden are seeing fat earthworms drilling around, and ladybugs — those voracious eaters of aphids — having lunch with the girls).
Out of sight, but not out of a gardener’s mind, are the invisible helpers: the naturally occurring organisms know as mycorrhizal fungi that form symbiotic relationship with the roots of many plants, and help them get water and nutrients, and be more disease resistant.
Terry says: "Think of it this way — when you take care of your soil, you’re putting the micro-herds to work for you. They need what we need: air, water, food and shelter. You’re feeding and protecting them.” Terry notes that there is a whole lot of life in healthy soil: one teaspoon can contain 100 million to 1 billion beneficial bacteria, and many yards of fungal hyphae.
Now, if after pushing back the mulch, you see that your cardboard or paper is still intact, don’t worry — you can plant right through it. Just slice an X in the material, peel it back, and plant your plant. Replace the mulch, but remember not to put it right up against the plant.
What type of compost is best? There are plenty of opinions. What you want is well-made and well-decomposed compost. Some places sell compost that is made of wood fines. That can work, but wood fines usually aren’t well composted; they need time to break down into soil. Check the labels and ask about what you’re getting.
Ideally, add compost twice a year — in the fall and spring.
Joan Tharp is a University of California Cooperative Extension Master Gardener. She lives in San Mateo. She can be reached at firstname.lastname@example.org.
Prepare your soil now and prepare for the San Mateo and San Francisco Counties Master Gardeners Tomato and Pepper Plant Sale. This very popular sale of tomato and pepper seedlings known to do well in our local area will be held 9 a.m.-1 p.m. April 14 at the Elks Lodge in San Mateo, 229 W. 20th Ave. Visit the sale website for more information: http://ucanr.org/sites/MGsSMSF/Special_events/Tomato_Sale