By Diane C. Kennedy, for Let’s Talk Plants! December 2022.
One of the largest issues with keeping a landscape alive is improper irrigation. Overwatering is usually the culprit for so many plant problems, which is ironic in these times of drought and water reduction. Unless you have a newly planted area where the plants have very small roots, plants shouldn’t be watered more than twice a week or less, even in the summer. The younger and shallower the root, the more frequently the watering needs to be so that they don’t dry up. However, deep watering will sink into the ground and those tender roots will follow and grow strong. Even lawn grass – if you still have any – should be watered deeply and less frequently and mown at three to four inches. Most established shrubs and trees need deep watering to drench the roots, with dry recovery times in between so that the soil can recharge with oxygen. This translates to watering once or twice a week during the heat of the summer, and maybe once or twice a month during spring, depending upon the species.
Drought tolerant native and Mediterranean plants don’t want a rich soil, so don’t use amendment when planting them. Rich soil holds moisture close to the roots. The symptoms for over- and under-watering are the same, so use your finger to test the soil several inches down to see if the plant needs more water or not. If there is any moisture in the soil, don’t water it. When the soil feels dry, then give the plants a good deep soaking.
Overhead sprayers use a lot of water and won’t allow water to sink into the roots of a plant. They will, however, water weeds. Tubing with holes in it will often water what you don’t need watered, will clog with minerals, and is usually buried so if it is nicked, twisted or bitten through becomes a nightmare to fix. Better options are to run PVC with uprights that have bubblers or small fans of water on the nozzles. If you attach two threaded elbows (street 90’s) between the PVC and the riser, you can move the sprinkler head in all directions. This is great for trees. For shrubs, run black tubing from a PVC system, and use individual emitters on spikes attached to the tubing with spaghetti tubes, and place the emitters above the rootball of the plant (if on a slope). These can be easily adjusted up or down for how much water they deliver, can be moved away from the stem or trunk of the plant, and are easily cleaned out when clogged with our mineral-rich water. The tubing can be covered with mulch so that you don’t see it (with every inch of mulch you can reduce your watering by 10%). Your plants will grow, and not the weeds. If you have problems with animals chewing on the tubing, use a natural animal deterrent spray on the heads and tubing.
Common signs of irrigation problems with fruit trees are water stains on the trunks where spray hits them, run-off, water-thirsty weeds such as plantain growing under the trees, fruit that may taste sweet but has a bitterness to it and doesn’t have a deep flavor (overwatering prevents mineral absorption by the roots) and yellowing of the leaves. Common signs of overwatering drought tolerant shrubs are abnormally fast growth rate which then leaves the tall plants weak and fragile, and sprawling plants brown in the center. High populations of Argentine ants are also an indicator of moist soil.
The only use for overhead sprayers is for grass (which you can receive good rebates for removing!), and for an established native landscape which only needs the simulation of a summer rainstorm during the hot months to remain hydrated. Having sprayers positioned around your house is important in case of fire danger. You can turn them on to hydrate your landscape and retard the spread of fire and give yourself time to evacuate.
Consider the sources of the water that you use; whole ecosystems have collapsed due to water being drained for home use. When we waste that water, or even our precious well water, through needless overwatering and unevaluated irrigation systems, we are harming our planet.
If you are unsure about your irrigation, then contact a Quality Water Efficient Landscaper (QWEL) who will do a sprinkler evaluation on your lawn. Or contact a permaculturalist who can give you great advice for irrigating with less water and for capturing rainwater in your soil.