What Not To Do
Don’t add amendment to permanent landscape areas or California native plant landscapes. Amendments are fine for areas that are harvested or replanted frequently, like vegetable or flower gardens. But in a landscape, it can do more harm than good by destroying existing roots and soil food web networks created by the beneficial soil critters. Additionally, amendments contain nutrients that your soil may or may not need.
When you dig a hole for a new plant, and add soil amendment around the roots of the new plant, you have created a “glorified pot.” This is because the soil of the root ball and the amendment are typically light and airy (large pore spaces) while the existing soil in which the hole has been dug is more dense and tight (smaller pore spaces). When water is added to the new plant and amendment, it will get sucked into the surrounding soil. This is because water is attracted to surfaces. The tighter, smaller pore spaces of the surrounding soil have greater surface areas in which to attract the water. If your surrounding soil is dry, the root ball of your new plant will dry out faster than if it were in a plastic pot! Additionally, the added amendment creates an environment that keeps roots from penetrating the landscape soil, ultimately causing the plant to become root-bound. The goal is to get the new plant’s roots established in the existing soil so the roots will grow beyond the planting hole.
Want to see how water moves?
Try this: Hold a paper towel vertically. Dip the edge of a paper towel in water and watch the water climb up the towel; or,
Put a drop of water on a flat impervious surface. Note how the water drop stays in a roundish “bump.” Now take your finger (or just about any object) and just barely touch the edge of the droplet. Notice how the droplet is pulled toward the object.