by Charlene Burgi
While we are not following the yellow brick road with Dorothy and friends, we are on a path that requires caution and attention to detail in the garden right now. The evapotranspiration rate is peaking, as is the solar radiation. Add extreme heat and we have a recipe for very unhappy plants if our irrigation amount or timing isn’t correct.
As I mentioned before, the peak season for irrigation is the end of June and beginning of July. This is when we have the most daylight hours. Our plants use this light to enhance their growth. It is also when they require the most water.
High temperatures during this time can create a problem. Normally, a plant draws up the available water and transpires excess through the leaves. (We perspire, plants transpire.) At the same time, water is evaporating from the soil around the plant. During a heat spell, even if there is available water for the plant to draw on, it can’t bring it to the leaves fast enough, and you will see singed edges or leaves turning crisp.
I could recite that information in my sleep, but I foolishly left some new plants in nursery containers out in the sun this week. They were sitting on bark waiting to go into the ground. They were watered the night before, but they were too little to take that kind of heat even though they were water-conserving plants. I even used the method of walking barefoot in the bark. The theory is if your feet can handle the heat, then so can plants growing in containers. Well, I will add a caveat to that idea: If the containers are black, and the plants are babies, keep them in the shade until they are in the ground. My experience, or lack of, resulted in several containers full of crisp leaves. Proceed with caution.
Caution also extends to irrigating in high temperatures. For the most part, water in the wee hours of the morning if you have an automatic controller. Set it so the last station finishes about 6 a.m. That gives the plants time to recharge before the sun starts beating down on them. It also gives the water drops on the leaves a chance to evaporate so the drops don’t become magnifying glasses and burn the foliage. This is why some people prefer watering in the evening. However, evening irrigation often brings up a red flag for me as some plants don’t like wet feet, and sitting in moisture all night can bring on fungus and other maladies.
While you are checking the timing of the controller, pay attention to where your irrigation water is hitting. Aim for the root systems of the plants. You have missed your target if your nozzles are directed onto the sidewalk, driveway or neighbor’s yard. Plant your water where the roots are located.
And speaking of proceeding with caution, last week I suggested using Buddleia to attract butterflies in the garden. In the far recesses of my mind, something was nagging at me about this plant. I want to thank one of our faithful readers for pointing out that we have Buddleia davdii listed on the MMWD invasive plant list. While I have not had mine “travel” in the garden, I respectfully recommend that you check Marin’s Cal-IPC list first before purchasing. My apology extends to our rangers and plant biologists for my blunder. May I suggest you opt for Asclepias tuberosa instead.
Speaking of butterflies, I want to share a photo of the beneficials you can attract to your garden by providing the right food. Unlike my withered plants, these babies will make it.