Autumn planting: get the dirt on soil prep

Considering converting all or part of your home landscape to water-efficient plants? With the planting season approaching—late summer and early fall are a good time to lay some groundwork as it were. Success in a sustainable landscape comes down to matching the right plant to the right place.

There are three variables that feed into the equation: light (sun and shade); soil (drainage and pH) and plant size. Plant size varies from plant to plant and is easy to determine from nursery catalogs, books and the Internet. The goal is to select a plant that will provide function (shade, screening etc.) and display (flowers, berries etc.) without needing constant pruning.

The August Getting Native segment offered insights on sun and shade; this segment offers some perspectives on soil.

Soil provides physical support for plants while at the same time provides their main source of moisture and nutrition. Garden soils vary from place to place just as plants vary in their tolerance of soils. So how can we tell what our garden soil will grow? The answer lies in understanding some basic properties of the soil. The physical structure (proportion of clay, silt and sand) and the chemistry (pH and nutrient profile) will tell you most of what you need to know. Some exceptions exist but, fortunately, these are rare.

A comprehensive soil analysis can be obtained from a soil laboratory and this is a good investment but, in most cases, not essential. Here are some basic tests you can conduct:

A percolation test will yield the next important property of the soil. How well does it drain? Is it slow (clay soil)? Fast (sandy soil)? Average (sandy clay)?

  • A simple 'feel' test can provide you with a good estimation of the physical structure. Is the soil mostly clay?, a mixture of clay and sand (sandy)?, silty?, etc.

Remember, the goal is to match the right plant to the right place. For example many of our Mediterranean climate plants, including California natives grow in fast draining, nutrient poor soils. If you find that your soil drains slowly and has a high percentage of clay, you will need to either improve the drainage or choose natives that will tolerate slower draining soils.

These are just basic insights into what is a complex subject. Further reading is recommended but we hope this will get you started and provide you with some information before you set about selecting plants.

Two new videos have been added to the Getting Native Facebook page to illustrate the tests we described above.

Pull on your gardening boots, dig in and find out what your soil is all about!

Next time we will discuss soil chemistry and round out this often-perplexing subject.