If you have ever put a shovel into the ground in San Diego County, you have likely encountered the region’s impermeable soils. Impermeable soils are defined by their poor infiltration areas. This means water doesn’t flow through the soil to replenish the groundwater, because the soil is too dense.  

It also means water doesn’t soak evenly into the ground or flow through living soil to plants in a healthy way. No matter where you do your landscaping, you should concentrate on improving your soil structure as much as possible. That will help irrigation be more efficient and more cost-effective, and your landscape plants will receive the nutrients and water they need to flourish. 

Why Does Particle Size Matter in Soils? 

 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 soils drain faster than clay soils, because there is more space between the larger 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.  
The “just right” soil – an even blend of sand, silt and clay – is called loam. 

Determining Your Soil Type Using The Jar Soil 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 storm water. 

You can test your home landscaping soil yourself using a “Jar Test.” This is a fun project to do with kids. 

1. Use a one-quart glass container. 

1. Add one cup of soil from the garden. You can select one area or take samples from several areas and blend them together. 

1. Add three cups of distilled water. 

1. Close the jar and shake it until all the soil solids are suspended in water. 

1. Put the jar on a shelf and wait 24 hours.  

1. If the container is still cloudy, wait another 24 hours. 

1. After 48 hours, the soil layers should be settled on the bottom. 

1. Measure the layers in proportion to each other, with the total adding up to 100 percent. 

1. 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. 

 Which jar does your home sample look most like? 

Now you can work to improve your soil condition, providing the best possible foundation for your landscaping plants and the most efficient irrigation.  

 

This article was inspired by the 71-page Sustainable Landscapes Program guidebook available at SustainableLandscapesSD.org. Hardcopies are available free of charge at the Water Authority’s headquarters, 4677 Overland Ave., Kearny Mesa. The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at WaterSmartSD.org.