As the weather heats up in May, gardening activity winds down. Discover what you can still plant, prune, and fertilize (and what you shouldn’t), how to adjust your watering schedule as you head into summer, and more.
May is a beautiful month in the desert. Plants are flowering and bursting with new spring growth. But as the weather heats up, gardening activities slow down.
While there are still plenty of gardening activities to be done in May, there are some tasks that you should skip for now — they are best done in cooler weather.
Let’s take a look at what you should and shouldn’t plant, prune, and fertilize, how to adjust your watering schedule, and more.
May Weather Outlook
Compared to April, May is noticeably hotter, drier, and harder on plants. (And on gardeners). The average high temperature is nearly 10 degrees higher. The chance of rain continues to go down, dry winds pick up, and the sun’s intensity increases.
Here’s a look at May weather averages in both Tucson and Phoenix.
May Weather Averages (Tucson)
| High temperature | 92°F |
| Low temperature | 61°F |
| Precipitation | .24″ |
| Relative humidity | 18% |
| UV Index | 10.4 |
| Wind | 15 mph |
May Weather Averages (Phoenix)
| High temperature | 95°F |
| Low temperature | 69°F |
| Precipitation | .13″ |
| Relative humidity | 18% |
| UV Index | 9.3 |
| Wind | 8 mph |
If you live elsewhere, enter your city or town in the search bar at TimeandDate.com to find your weather averages. And you can find your average UV index at UVIndex.io.
What To Do in the Garden in May
Here’s a snapshot of the activities you can do this month, and those you should stop doing.
| ✅ | Plant palms, succulents, summer annuals |
| ✅ | Divide aloes, agave pups |
| ✅ | Adjust water schedule |
| ✅ | Do light pruning |
| ✅ | Fertilize palms, some citrus |
| ✅ | Harvest wildflower seeds |
| ❌ | Don’t plant most plants |
| ❌ | Don’t prune most plants |
| ❌ | Don’t fertilize most plants |
Read on for all the details and exceptions!
What You Should (& Shouldn’t) Plant in May
The list of what you should plant in May is a small one.
Some plants should be planted in May. It’s an ideal time to plant cactus, agaves, and other succulents since warm soil encourages root development. You can move agave pups and divide clusters of aloe now as well.
May is a great time to plant summer annuals such as gaillardia, gomphrena, pentas, moss roses, sweet potato vine, vinca, and zinnia.
While you “can” continue to plant native or desert-adapted trees, shrubs, ornamental grasses, and perennials, planting now is not ideal, and I don’t recommend it.
There’s not enough time for plants to get acclimated and summer is just too darn stressful for new plants.
But if you do plant in May, be sure to give your new plants some extra TLC. Learn how to minimize planting stress and get your plants off to the best possible start in our article 7 Steps for Successful Spring Planting.
Adjust Your Watering Schedule Mid-Month
If you look at various watering charts like the one below, you’ll find that spring is considered “March through May” while summer is considered “May through September”.
Since the past few years have been getting hotter earlier, I suggest adjusting your irrigation to a summer schedule early in May.
As the weather heats up, it’s critical that you’re watering correctly. Use the University of Arizona’s Recommended Watering Schedule as a simple guide or Landscape Watering by the Numbers flipbook as an in-depth guide.
For more help on how to water your plants in May,
check out these articles:
How & Why to “Deep Water” Desert Plants
How to Water Desert Trees: How Often? How Much?
How to Water Desert Shrubs: How Often? How Much?
7 Tips for Watering Landscape Cactus (& Other Succulents)
What to Fertilize
May is the perfect month to fertilize palm trees. They need warm soil to absorb nutrients. Continue to fertilize potted succulents once a month. You can fertilize potted annuals every two weeks now, too.
Citrus
Citrus should be fertilized three times per year. Orange and grapefruit trees should receive their third dose of fertilizer sometime in May or June.
There’s more to fertilizing citrus than haphazardly sprinkling fertilizer around a tree. Learn how to fertilize citrus for best results in our article How & When to Fertilize Citrus Trees.
While we’re talking about citrus, don’t be concerned if your trees lose older yellow leaves or drop premature fruit this month. Your trees are smart — they only keep the amount of fruit that they can comfortably support.
And if you see something on your citrus leaves that looks like a blob of bird poop 💩, please leave it be. It’s the larva of the beautiful giant swallowtail (Papilio cresphontes) and will only cause minor cosmetic damage. This is one of the largest butterflies in North America — they can be up to 6″ across! — and we are fortunate to have them here.
If you want butterflies, 🦋
you gotta put up with caterpillars! 🤗
What to Prune
Other than cactus and other succulents, which prefer to be pruned when it’s hot, now is not the time to do much pruning.
You can prune spring-flowering shrubs that have finished blooming, such as fairy dusters, brittlebush, chuparosa, and the various emu bush species.
You can lightly prune trees and shrubs to shape or remove the 5 Ds — dead, diseased, damaged, dangerous, or deranged branches.
You can continue to deadhead annuals and perennials to encourage flowering. And you can pinch them back as they grow to help them become bushier.
Watch for Weeds
Weeds aren’t usually much of a problem in hot, dry May.
But if you live in Arizona or southern California, continue to keep an eye out for stinknet, an alarmingly aggressive, invasive plant that threatens desert biodiversity, contributes to wildfires, and emits toxic gases when burned.
It’s an annual that is on its way out by now, but if you find it on your property, it’s urgent that you act before it goes to seed so you don’t have an even bigger problem next year. Learn how to identify it and get rid of it at Stinknet.org.
Upcoming Gardening Events in May
There are still some gardening classes and events throughout May, but activity, which peaks in April, is winding down. You’ll find a comprehensive list of nurseries, botanical gardens, and organizations that hold classes, events, and sales in our Tucson Gardening Events Calendar.
Don’t live in Tucson? Look for Zoom classes. You can participate in these no matter where you live.
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for over 15 years.
