Plants aren’t that different from the rest of us in many respects. When it is very hot outside, we need shade, sun protection and hydration, and so do our gardens. Plants carry some tools with them to deal with sun, heat and wind. Many develop light or grayish leaves or fuzzy leaves that act as sunscreen. Some rotate their leaves away from the sun all day like little anti-solar panels. Some just go dormant in summer, a plant’s version of hibernation. But when temperatures climb to 100 degrees and above, most plants appreciate some extra assistance. There are several things you can do to help your plants withstand the weather.
Bark chips, grass clippings and old leaves are all great for helping soil retain moisture. Mulch also creates shade, which keeps the soil cooler. If you use old grass clippings or even straw, the light color will even help to reflect sunlight. Mulch also helps protect soil from wind seeking to dry it out. Use a two to three inch layer for best results. Use mulch made out of biodegradable materials that will decay over time and feed the soil. If you use rocks as a ground cover, don’t add mulch to this. You are already helping your plants. Even rocks provide shade and help to keep moisture in the soil.
Be careful to keep the mulch away from the immediate area of the plant’s stems or tree trunks. Mulch is so good at retaining moisture that if it’s too close to the plant it may contribute to fungus or root rot. And just pour the mulch on top and rake it – don’t mix it into the soil or it will pull nitrogen (nutrients) out of the soil as it decays.
Set up a shade structure
Shade cloth or row cloth is often seen in vegetable gardens, but I also use it for ornamental plants, particularly when the planting is less than a year old. I build tiny shade structures out of a sheet of 30% shade cloth, dowels and garden ties or staples, although I’m sure there are many ways to do this. It helps to position the cloth to the south or west side of the plant or directly above it. Make sure you’re giving the plant room to breathe, and don’t forget to remove the shade cloth when the heat wave is over.
Water early and deeply
Water as early in the day as possible, particularly if you have sprinklers since most sprinkler water is lost to wind and evaporation during hot times of the day. Additionally, watering leaves when the sun is directly overhead can cause leaf scald. Watering too late in the day is deadly for many plants. For low-water plants that are adapted to dry summers, sitting in warm soil and being damp at sunset and into the evening is a recipe for fungal infections that can lead to root rot or sudden death.
Using drip irrigation or soaker hoses (or just a hose laid on the ground) gives you a lot more flexibility. Leaves don’t get wet and if positioned correctly, the plant itself will not get as wet so watering during the day or early evening is not as harmful.
How much water to give your plants during a heat wave depends on the type of plant and how long the plant has been in the ground. If I have designed your garden, you have low water plants that will not appreciate being deluged during a heat wave any more than they would at any other time. What they will appreciate is an extra long, slow watering or two during the week. Drip irrigation, soaker hoses or just a trickling hose set next to plants are the best ways to deliver extra water.
Plants that have been in the ground less than two years are still developing a strong, deep root structure. The heat drying out the top few inches of the soil has a bigger impact on them. Take extra care to keep that top layer from drying out into an impenetrable brick. Only you know how quickly your soil dries out, but maybe increase to watering three times a week during very hot or dry weather. Young trees should get two to four inches of water per week once temperatures hit 100 degrees. Again, a trickling hose or soaker hose is best for this supplemental water.
Prepare when you can
After two years when plants are well established and their roots are deep, you should be able to water deeply one additional time per week when it’s really hot and/or dry. Many of you only water monthly in the summer, so just do one deep watering a week in extreme heat.
If you’ve done the work to water deeply and infrequently the prior two years you have helped your plants to set up deep, extensive root structures and are set up for success, so pay attention to your soil as you are establishing your garden. It will pay off later.