Help Your Plants Survive the Tucson Summer Heat | Home & Garden

Tucson has five seasons: winter, spring, dry summer, wet summer, and fall. Our dry summers can be rough on plants—even native ones. This is particularly the case on urban lots, where the urban heat island effect results in temperatures several degrees higher than outside the city. Reflection from sidewalks and windows increases stress.

Native plants usually tolerate our conditions best. If you plant non-natives, they should be drought tolerant. If you have non-natives that are not drought tolerant, you will likely need to water them at least once a day and provide 40-60% shade. Even with these precautions, some non-native plants will not survive our summer because they cannot photosynthesize at high temperatures. Many large chain-based nurseries sell plants that are not viable in our climate. The best thing to do when purchasing plants is to go to a local garden center. You can also check out this guide to drought tolerant plants.

Once you have your plants, you can protect them from the worst of the heat and drought by following a few simple tips:

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Make sure you water your plants down to their root zone. For trees, this means 3 feet deep; Shrubs need to be watered up to 2 feet, and smaller plants and cacti need about 12 inches. Infrequent deep watering is always better for plants than shallow, frequent watering. How do you know how deep you are irrigating? Use a soil probe (a thin rebar metal rod with a handle) to check. Just stick the pole into the ground and see how far you can push it in. See this handout for detailed instructions. You can get soil probes at some nurseries or at the Master Gardener Demonstration Gardens. To find out how often to water, read these helpful guidelines from the City of Tucson. Remember these guidelines are for established plants and average sandy loam soil. Your soil type may require a different watering system.

mulch. And then mulch some more. Mulch protects the soil from erosion caused by wind and rain, keeps the soil cooler, and helps retain moisture. It also controls weeds and reduces soil compaction. You’ll need at least 2-4 inches of organic mulch (like bark, wood chips, etc.) or 2-3 inches of inorganic mulch (like gravel or decomposed granite). You can read more about mulching options in my article.

Do not prune in the summer months (except for safety reasons or when the branches are diseased or broken). Pruning signals plants to start growing more leaves at a time when roots are particularly stressed.

Avoid fertilizing. Packaged fertilizers and manure contain salts that, when added to the soil, reduce the ability of plant roots to absorb water. If you feel your plants are in dire need of nutrients, add vermicompost or well-aged compost – just make sure you water it well.

Check your irrigation system regularly and fix any problems immediately. In our hot, dry summers, it can only take a day or two for a plant to die from lack of moisture. This is especially true for non-native plants. I like to take a tour of my garden in the morning every other day to see how everything looks. That way I can quickly spot any problems and (hopefully) fix them before something dies. I can also give stressed plants extra water before the heat of the day.

Prioritize your big trees as they give you the best bang for your buck. They provide much-needed shade for your other plants (and you) and lower temperatures in your garden and home. If you have trees (even native ones) near sidewalks, walls, or windows, they will thrive better with a little extra watering. Make sure they get a nice deep watering (up to 3 feet!) every few weeks during the dry summer. Also, make sure you water near the tree’s drip line, not near the trunk.

Don’t overwater. Too much water in the soil means there are no air spaces between the soil particles and the roots have no access to oxygen. Once the roots die, the plant is lost.

Don’t be afraid to use shade fabrics and shade textures. In nature, plants are often shaded by the overgrown trees, but this is often not feasible on urban lots. Extra shade, especially in the afternoon, can mean the difference between death and survival for borderline plants.

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