Tips for Native Plant Heat Wave Gardening

Now that last summer’s extreme heat is behind us, it is time to take stock and see what we have learned. Although I have seen numerous articles (here and here – thank you, Jane S. for sharing these) on garden tips for nonnatives, including subtropicals, vegetables, and fruit trees, I have not found much related to native plant gardening. Below I have laid out some tips for pre, during, and post-heat wave gardening with native plants. I also made an inventory of my garden plants that survived and those that didn’t.

Before the heat arrives

Water thoroughly. You want the water to reach all parts of the plant before the heat because during times of extreme heat, plants shut down metabolically. Furthermore, watering when it is very hot can increase activity of soil pathogens. In simple terms, if you water during the heat wave, the plant is thirsty but it can’t drink, and its roots may rot.

Do not water summer dormant plants. Let them sleep through the inclement weather and don’t  encourage the growth of soil pathogens.

During the heat wave

Provide shade. This is especially important for young plants and plants with fine, delicate leaves. Shade may keep the temperature down a bit, particularly if there is some moisture from earlier watering. A tarp or shade cloth may be especially helpful in areas that receive reflected heat from buildings, walls, and other built structures.

Dampen the shade cloth. Spray lightly with water to reduce the temperature, though when it reaches 114ºF it is very hard to keep up with the rapid evaporation.

Dampen leaves and ground. Spray leaves and ground to help reduce the temperature. This may be a bit controversial since I have read that water droplets on leaves can actually magnify the sun’s rays causing more leaf burn. I realize that water droplets can act like small magnifying lenses, however, I have never noticed leaf burn from water droplets. If anyone else has, please make your case.

A light spraying of water on the ground may help to reduce the temperature so that surface roots are less likely to burn. Again, it may be hard to keep up with extreme heat. Do not soak the area during the heat wave since this can have bad consequences as noted above.

Once it cools down

Do not rush to remove burnt or dead leaves and branches after the heat wave passes since the dead material will continue to shade the plant below. It is hard to look at the scorched leaves but be patient.

As the weather moderates water plants according to their needs. Wait until summer-dormant plants reawaken before watering. Water deeply and occasionally during the winter if we do not get a good amount of rain. These plants have been stressed and their best chances in the future rely on good watering practices during the winter growing season.

Now that summer is over, it is time to really assess your garden. What plants made it? Which ones struggle or just couldn’t hack it. Were they established plants? Do you think that they will do okay once they become established (assuming we don’t have another brutal summer)?

I think we can assume that climate change means that the weather will fluctuate more than we are used to. We may get more extreme heat, more extreme cold, years with heavy rains and others with almost none. These conditions are hard to plan for and we are likely to see more losses, especially in our urban trees. Nonetheless, plants will grow, and what we need to do is pay attention so that we can figure out the best way to garden in changing times.

How my native plants did

We were away from mid-July (after the 114º heat wave) to the end of August. The yard gets little or no summer water. In our absence, a gardener was checking on things, especially new plantings and mature trees. I used a Skydrop controller to remotely set off irrigation for our fruit trees, the front yard deodar, and the vegetable garden.

Below are two native plant lists: One for new plants, those  less than two years old, and one for established ones. Each list includes the following categories: Died or nearly so, scorched or slowed down but should be okay, and unfazed by the heat. To keep it simple, I am using common names. I’d love to hear what worked and what didn’t in your gardens.

New plants

Died or nearly so

1. coral bells
2. Russian River coyote mint
3. Margarita BOP penstemon
4. yarrow (may come back)
5. western columbine
6. California fescue (some made it)

Leaf burn or slower growth but should be okay

1. Cleveland sage
2. Emerald Carpet sage
3. Eve Case coffeeberry
4. wooly bluecurls
5. showy penstemon

Did well

1. Desert Museum palo verde
2. San Bruno Mt. golden aster
3. creeping barberry
4. sticky monkeyflower
5. annual sunflower

Established plants

Died or nearly so

1. Margarita BOP penstemons
2. western columbine
3. coral bells
4. California fescue (some made it)
5. California goldenrod (may come back)
6. A weak avocado may be a goner – hopefully not

Leaf burn but should be okay

1. toyon
2. holly-leaf cherry
3. Catalina perfume
4. Roger’s Red wild grape
5. Skylark barberry
6. California fuchsia
7. Pacific Coast hybrid iris
8. fuchsia-flowering gooseberry (went dormant)

Did well

1. coast live oaks
2. bladderpod
3. deergrass
4. alkali dropseed
5. sticky monkeyflower
6. California buckwheat
7. Palmer’s Indian mallow
8. cane bluestem
9. flannelbush
10. Ray Hartman and Joyce Coulter California lilac
11. manzanita

How does your garden grow?

Penstemon ‘Margarita BOP’ never did well in my garden – too little water

Deergrass, CA fuchsia, woolly sunflower are all healthy but summer dry.

Desert marigold is going great with no assistance.

Sticky monkeyflower, deergrass, CA fuchsia are all summer dry.

Skylark barberry looks great with little water. Older Eve Case coffeeberry burned out several years ago.

New Eve Case coffeeberries replacements planted beneath older ones that declined after the loss of shade from an old, diseased and now deceased avocado.

Front yard, east side

Dormant fuchsia-flowering gooseberry

Front yard, west side