We wanted to take a minute of your time and discuss the effects of the heat on our plants right now. We are amid the “hottest summer and the 3rd driest year on record”. We have all seen the effects of the dry extreme heat on many of the plants in our pallet here in the valley, I want to talk briefly about the reason’s things look so rough.
The processes a plant goes through to create energy or food to sustain itself is called photosynthesis, which we all know from High School Biology. The process requires some basic functions by the plant to make this happen; while we know plants need nutrients and water from the soil, and sunshine and C02 from the air, they also need to have a “rest period” to make this process happen.
When everything is working right for plants, they will exchange gasses and moisture through openings in the leaves called stomata. When the weather is nice, this exchange happens all day and night but when it gets hot, dry, and windy, the stomata will close during the day to conserve moisture which reduces photosynthesis. After the sun goes down, the stomata open back up and the plant catches up on its needed processes to make energy for its survival. When the weather is this extreme, the plants close the Stomata during the day as normal but when the nighttime temperatures stay too high and humidity levels too low to allow for the stomata to open and allow gas exchange and the plants begin to suffer due to the plant surviving on stored reserves.This suffering is shown through yellowing of the overall plant, leaf decline and defoliation.
We are seeing the biggest impact on plants like Lantana, Oleanders, Cape Honeysuckle, Ficus trees and other more tropical plants. The tough hardened plants that are desert adapted such as Texas Rangers, Cassia and Jojoba are thriving as they have developed systems to handle such extremes.
Soil hydration is always a critical factor in the plants ability to come out of this when the season starts to cool, but it is also critical not to over saturate the soil with water and “suffocate” the roots. We monitor the soil moisture levels along with published ET (evapotranspiration) rates and adjust as the weather and plant needs dictate.
Plant location plays a huge roll in how it handles these extremes. As we travel around the valley, we have noticed that many plants look much healthier where they receive some shade. We have noticed long rows of stressed lantana along roadways, but under and on the east side of trees they are green and viable. Outside factors such as reflected heat from walls, asphalt and concrete sidewalks exacerbate the problem and act as heat sinks.
There is light at the end of the tunnel. The extreme weather will subside and all our plants (we hope) should come out of the stressed state they are in and they will start getting ready for the opposite extreme of winter.
Horticulturist, Certified Arborist (7119A), TRAQ, ACLP, CDLP, QA, CTP, CMG, SLM, Smartscape,
Director of Maintenance