Compare your soil to these diagrams to determine your landscaping's soil composition. You can then adjust amendments to reach the optimum mix. Illustration: SDCWA Jar Soil TestCompare your soil to these diagrams to determine your landscaping's soil composition. You can then adjust amendments to reach the optimum mix. Illustration: San Diego County Water Authority

Improve Your Landscaping Soil With a Soil Test

One of the first steps in your landscape makeover project involves preparing the soil to allow efficient use of irrigation. San Diego County soil quality needs a lot of help. The area is defined by impermeable soils with poor infiltration areas. Water doesn’t flow through the soil to replenish the groundwater, because it is made primarily of clay which is too dense.

In impermeable soils, irrigation doesn’t soak evenly into the ground, or flow through living soil and plants in a healthy way. No matter where you do your landscaping, you need to put in some work to improve your soil structure as much as possible. Irrigation will be more efficient and more cost-effective, and your landscape plants will receive the nutrients and water they need to flourish.

Check for particle size

Before you can build better soil, you need to figure out what type of soil you are working with. The three basic types of soil are:

  • Clay: Soil made up of the smallest particles
  • Silt: Soil made up of a mixture of particle sizes
  • Sand: Soil made up of the largest particles

In general, sandy soil drains faster than clay soil, because there is more space among the larger sized particles. Soil structure also influences soil quality. Lifeless, compacted sandy soil will not absorb water, while healthy clay soil will be more sponge-like, holding and releasing water when needed.

Learn your soil type using the jar test

Some tests can be done onsite to figure out what kind of soil you have. Others require lab analysis. Certain conditions require specialized tests, such as soil used for food production or soil receiving a lot of stormwater.

For most landscaping projects, you can test your home landscaping soil yourself. Watch the video, then follow these directions for a “Jar Test.” This is a fun science project to do with kids.

  1. Use a one-quart size glass container.
  2. Add one cup of soil from the garden. You can select one area or take samples from several areas and blend them together.
  3. Add three cups of distilled water.
  4. Close the jar and shake it until all the soil solids are suspended in water.
  5. Put the jar on a shelf and wait 24 hours.
  6. If the container is still cloudy, wait another 24 hours.
  7. After 48 hours, the soil layers should be settled on the bottom.
  8. Measure the layers in proportion to each other, with the total adding up to 100 percent.
  9. Sand will be on the bottom, silt in the middle, and clay on top.

Refer to the graphic to determine your soil type, based on the proportions of sand, silt, and clay.

Compare your soil to these diagrams to determine your landscaping's soil composition. You can then adjust amendments to reach the optimum mix. Illustration: SDCWA Jar Soil Test

Compare your soil to these diagrams to determine your landscaping’s soil composition. You can then adjust amendments to reach the optimum mix. Illustration:  San Diego County Water Authority

Which jar does your home sample look most like? You will be able to work with your soil type to improve its condition, providing the best possible foundation for your landscaping plants and the most efficient irrigation.

This article is part of a year-long series inspired by the 71-page Sustainable Landscapes Program guidebook available at SustainableLandscapesSD.org. The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at WaterSmartSD.org.