By Nick Stavros, for Let’s Talk Plants! April 2023. Originally published in March 2010, No. 186.
Protecting your Garden from Storm Damage
The heavy rains in January 2010 caused a minimal amount of damage in our very wooded garden. To me, there are two basic problems with heavy rains: excess water and plant damage. Excess water can cause erosion and flooding. The best way to prevent erosion is to use extensive terracing and then to use the appropriate planting materials, such as water absorbing and soil stabilizing mulches. Terracing is a tricky task: too much and with the wrong materials and your garden can look more like an industrial site. Too little, and you can look like you are holding on for dear life (figuratively and literally)!
We use natural local stone to do our terracing. Sometimes there are very distinct rock walls, usually no more than two and half feet tall. Other times, our terraces are natural-looking rockeries. We also don’t want to lose all that very valuable water through runoff. So, the flat surfaces that provide a bit of back slope can act as small basins that allow the water to slowly percolate into the soil.
Yes, we are very fortunate to have excellent textured soil that does have a fairly rapid percolation rate. In addition, we use natural, loosely fitting pavers and cobblestones underlaid with sand so that all walkways and patios help absorb water. Lately we have combined our need to save water into our rock walls and rockeries by using succulents and grass and grass-like plants. This provides us with vegetative interest as well as excellent slope stabilization.
Plant damage is often caused by too little pruning, especially in the fall. Many trees and their leaves become desiccated during the long, hot, dry fall. Often, the trees look just fine, but they have lost a phenomenal amount of water. So, when the first heavy dew comes in the fall they start making up for lost time, and the crown that was acceptable in the summer becomes top-heavy in the fall.
The problem is only exacerbated with rain. This causes branches to self-prune, and trees with inadequate root balls to fall over. Add onto the increased weight of the crown the fact that the increased rain reverses the illuviation* and calcification** of the soil, making it soft and friable and consequently a poor foundation for the existing trees.
The benefits of proper pruning are generally healthier plants and also a reduced fire risk. So, dead and low ground-hugging branches that trap leaves and trash are the first to go. Next, a good thinning of most of the trees and bushes is called for. This includes the obvious trees such as eucalyptus, pepper trees and acacias, but also our denser bushes and shrubs such as roses, Rhaphiolepis (Indian hawthorn), Buddleia (butterfly bush), Arctostaphylos (manzanita), and Ligustrum (Texas privet).
One last major preparation before the heavy rains besides mulching, pruning and terracing... is feeding your plants. This is when we use bone meal on bulbs, blood meal on nitrogen lovers, coffee grounds in lots of places and some strategic fertilizers for citrus, camellias and roses. However, make sure all such compounds, organic or not, are mixed into the soil and preferably watered in. Algae in the streams don’t care if the nitrogen and phosphorous that they receive is organic or not... they grow!! So, keep the growth in the garden, not in the water!
* Illuviation is the movement of soil material from one horizon to another in the soil profile.
** Calcification is a soil process where the surface soil is combined with calcium by the decomposition of plants.