In the Garden:
Northern California Coastal & Inland Valleys
March, 2001
Regional Report

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The beautiful gardens at Filoli are open to visitors starting in February.

Soil Basics

The temptation to plant my summer garden is overwhelming right now. The days are getting longer, the air is sweet with the scent of spring-flowering plants, and nurseries are bursting with enticing displays. However, I know from experience that I'll have much better results if I wait a few more weeks until the soil has warmed. So now is the perfect time to work the garden soil to get it in perfect shape before the final push of planting.

The Importance of Soil

Soil is the foundation of your garden. The more time you spend preparing your soil prior to planting, the easier and more rewarding your gardening will be. This is especially true for arid climates that receive no rainfall in the summer months and have only a thin layer of topsoil, which is where most nutrients are for plants. Topsoil is formed over many thousands of years by decomposing plant matter, but in arid climates, there just isn't much organic matter growing to fall to the ground and decompose.

Soil Types

Soil types differ throughout Northern California: sandy and fast draining along the coast, and clay-like and slow draining in the valleys. You need to determine exactly what type of soil you have before you can begin to improve it. Assess your garden area - even if you have sandy, fast-draining soil, for example, low-lying areas may stay wet longer than the rest of the garden. If you try to grow arid plants in boggy soil, you'll be throwing your money away and killing perfectly good plants. On the other hand, high spots drain more quickly than level ground, so choose plants that grow well in dry areas if you're planning on a rise.

Testing Your Soil

Here is a simple soil test to determine what kind of soil you have in your garden. Wet a small handful of dirt and roll it around in your hand. If it feels silky and slick, and stays together in a cigar shape, your soil is mostly clay. Clay is rich in nutrients but so dense that water, air, and nutrients have a hard time getting to plants. Plus, plant roots don't thrive because they can't push through thick, clay soil. The solution is to add river sand or organic matter to loosen the clay soil and allow air, water, and nutrients to flow more freely.

If the soil feels gritty and won't hold together when rolled in your hand, it's mostly sand. Sandy soil drains well but lacks nutrients. To improve the moisture- and nutrient-holding capacity of sandy soil, add organic compost. If the soil crumbles easily, but you can still roll it into a cigar, it's called loam, which is the ideal mixture of clay, sand, and silt.

Adding Organic Matter

The key to amending almost any type of soil is organic matter. Organic means any material that was once alive or is a by-product of something that was alive such as manure. It increases drainage in heavy clay soils, improves nutrient-holding capacity in sandy soils, and improves the texture of any soil, making it more crumbly and workable (friable). Organic matter comes in many forms, such as straw, leaves, manure, and grass clippings. If you have a source of organic material nearby - such as a horse farm or a dairy - you are in fat city!

Adding Manure

Manure is a rich source of organic matter. It not only supplies some fertilizer to soil, but it also improves the texture. It's best used in a composted rather than fresh form. I like to lay the manure over the soil in the late fall so that by spring the material has decomposed and is ready to turn under. If you don't have manure available, you can buy it in bags at garden centers and nursery supply stores. Composted manure is inexpensive and usually has been sterilized so it's easy to handle with very little odor.

Take a Soil Test

After you've amended the soil, take a soil test to see what nutrients, if any, you need to add. Professional soil tests are accurate and may actually be cheaper than the home soil-testing kits you find at the nursery. Agricultural extension offices provide this valuable service at a minimum cost. They will give you instructions on how to take a soil sample from your garden. Based on the results of the soil test and on what you're growing, you may need to add other nutrients or minerals to your garden.


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