I have quite a few potted plants, and right now I wish they were all in the ground.  The heat and the UV are stressing them and me.  This summer's weather has tested my methods of trying to keep potted plants alive in ways that no other summer seems to have accomplished. Here are some thoughts on how to keep your container plants going through another over-heated summer.

Watch the weather report and water your plants deeply in the early morning the day before the actual heat starts. If using a hose, check the water temperature coming out of the hose before it hits your plant's roots.  A garden hose can retain some serious heat! Let the water cool off before watering plants. During a heatwave, containers often need to be watered in the early morning and in the evening, because the soil dries out.  Keep the water off of the leaves and soak the plant until you see the water running out the bottom of the pot.  Make sure your effort is actually doing what you want.  I use a moisture meter and check several spots in each container.  If the soil is completely dried out, water will sometimes run down the inside edges of the container out the bottom and won't actually penetrate the roots.  That moisture meter has been a plant lifesaver. Another advantage of using the meter is that it keeps me from overwatering which can also kill the plant.  I usually water with a watering can so I can avoid hitting the leaves trying to prevent problems like powdery mildew or leaf burn. Don't forget to empty plant saucers after watering.  Saucers are shallow and heat up quickly on hot days.  In addition, emptying the saucer helps cuts down on the mosquito population.

If the plants aren't already in the shade and don't weigh a lot, consider moving them into a shaded area or to a north facing wall.  If that's not an option, 30% – 50% shade cloth supported with poles so the cloth isn't touching the plants can help.  If you already have tall, healthy in-ground plants that cast a shadow throughout the afternoon, move your containers into that shadow. Last summer, I regularly walked by a home with a new west-facing garden with a newly-planted Japanese maple tree.  The home owner erected a huge beach umbrella over the approximately 4-foot-tall tree during the entire summer, and it has survived and is quite a bit taller this year.  The key is to block as much of the mid-day sun as possible.

Heat-stressed plants are a smorgasbord for pests.  Keep an eye out for them and hand-pick the critters if seen.  The urge is to hit the plant with an insecticide, but sometimes that can actually contribute to the plant's demise. Most insecticides warn against using during temperatures above 90.

A good layer of mulch will help protect plant roots.  If the containers can be set on soil and mulch placed around the pots, the roots should stay cooler.  Having a big enough pot so a thick layer of mulch in the pot can help the plant.  Remember to keep the mulch from actually touching the plant stem.

Consider the plant container.  Terracotta isn't the best when trying to keep your plant alive during a heatwave.  It dries out quickly and so does the water you applied.  Sealing terracotta before planting can help.  Plants often come home from the store in thin, black plastic pots that also heat up significantly in the sun.  Move them to a shaded area until you can repot a plant into another safer container on a cloudy day.  Make sure to mulch them well when planting.  Larger pots don't dry out as quickly.  Pick big, thick plastic or heavy ceramic pots with decent-sized drainage holes. Self-watering plant containers could help.

Pick plants for containers that are drought-tolerant.  Some examples are grasses, African daisies, Mediterranean herbs like lavender, rosemary and salvias, and succulents.  If you have a fruiting plant or tree in a container, remove the ripe fruit so the plant can put its effort into survival. 

Plants will often have wilted, curling brown leaves as the heatwave drags on.  Your urge may be to whack off the dead parts and give the plant a shot of fertilizer.  Hold on!  The dead part can protect the living part from further burning.  Refrain from fertilizing until temperatures drop below 90 during the daytime.  Fertilizer pushes the plant to grow, stressing the plant even more.

A heatwave will eventually end.  Even if your plants don't look like they have survived, give them time for recovery.  We don't all pop up after being outside in the heat, and neither do they.  Enjoy your time indoors with a cold drink, a good book or a challenging puzzle and wait it out.  Eventually, we'll be complaining about how cold it is outside!