Arizona Garden in May Task and Heat Prep Guide

This blog post is your guide to May gardening in Arizona’s low desert. Learn what to prune, when to fertilize, how to adjust your watering schedule, and the best ways to protect your garden from rising temperatures.

As the heat sets in, May brings some of the most important garden tasks of the year. Mulching, watering deeply, and adding shade can make all the difference in helping your plants survive the looming high temperatures. Wondering what to plant this month? Head over to the What to Plant in May blog post for a detailed list.

May is the month to shift from spring production to summer survival in the low desert.

This guide is designed for low-desert gardeners in the Southwest—including areas below 3,500 feet in elevation, such as Phoenix, Tucson, and surrounding communities. Find all my desert gardening resources in one place on the Desert Gardening page.

Vegetable Garden Tasks in May

Prepare & Plant

• Prepare garden beds before planting summer crops. Add compost and worm castings to improve soil health, and mix in a balanced organic fertilizer if needed. Focus on the beds that struggled during spring.
• Use shade strategically. Some years I put up shade earlier, but May is usually the latest that I get it put up for summer. Here are my shade cloth resources.
• Apply mulch once your summer crops are growing well. I add a thick 3-5 inch layer of mulch to my garden beds before summer. It makes such a difference to have that mulch in place before the worst heat arrives. I put mine on top of my watering grids so the water doesn’t have to go through the mulch to reach the soil.
• Start seeds indoors this month if you want tomatoes for monsoon planting. Check my low desert planting list to see what else you can start from seed indoors this month.

Harvest

• Tomatoes are usually ready to pick throughout May. Once nighttime temperatures stay above 75°F, fruit set slows, but existing fruit will continue to ripen. When it gets hot I like to take my tomatoes indoors to finish ripening once they start to turn color. They tend to last longer that way.
• Beans are best harvested when the pods are small and tender. Overgrown beans don’t taste good! My kids love beans unless I leave them on the vine too long.
• Garlic and onions are typically ready to harvest this month.
  → How to Harvest Garlic
  → How to Harvest Onions
• I’itoi onions can be harvested now or left in the bed. I leave mine in the ground until the tops completely die back. It takes patience, but that rewards you with the longest storage life.

Pest & Plant Care

• Watch for squash bugs on summer squash. Check the undersides of leaves daily for clusters of eggs and adult bugs. If I see a squash bug in my garden, I keep checking, because when there is one there is always more! Get more tips for controlling squash bugs here.

Summer Transition Tips

• Consider using cover crops for any garden beds that won’t be planted this summer. As I harvest crops if I don’t have plans for that area, it’s easy to plant a cover crop there and let it grow until I’m ready to plant in the fall. That keeps the soil microbially active and makes it easy for me over the summer.
  → Learn more about summer cover crops

Vegetable Watering Guidelines

• As temperatures heat up, annual vegetables will need more frequent watering. Water to a depth of about 8-12 inches every 2-5 days; allow the top of the soil to dry out before watering again. 
• I use the garden grids from Garden in Minutes to water my raised beds.

For May maintenance, heat prep, and tracking in one spot, learn more about the Low Desert Garden Planner or buy it in my shop.

Container Gardening

Prepare for Summer Heat

I grow a lot of my favorite cool season flowers in containers so I can let them bloom as long as possible. When they finish up I usually put those containers away until the fall. May is a good time to evaluate your container setup for summer. For more container gardening tips, refer to my comprehensive guides to container gardening.

• Put small containers away until fall—they dry out too quickly in the summer heat. You can repurpose the soil as mulch in garden beds or add it to your compost pile.
• Move remaining containers to areas that get natural afternoon shade, like the east or north side of your yard.
• Group containers and grow bags close together to help insulate them and reduce heat stress.

Watering & Soil Care

• As temperatures rise, monitor containers closely and water frequently.
• If soil dries out completely, it can become hydrophobic (repelling water). Always check that water is soaking in and not running off the surface.
• Consider adding ollas (unglazed clay watering pots) to help maintain moisture. I use ollas from Growoya.

Fertilizing Containers

• Feed container plants about once a month with a low dose of water-soluble fertilizer. Containers lose nutrients more quickly due to frequent watering. I use Agrothrive for my containers.

If you enjoy container gardening, you may like the benefits of elevated beds, check out my guide, How to Grow in Elevated Garden Beds, to learn how to get started.

New to gardening in the heat? Elevated Garden Bed Tips for Hot Climates will help you if you’re gardening in containers or elevated beds. They can be trickier over the summer.

Flower Gardening

I love the blooms in May. The garden seems to be exploding with color as the last cool season flowers hang on a little longer and the summer flowers are just getting started. My garden is often a mix of sweet peas and wildflowers giving their last few blooms along with the first blooms from Shasta daisies, zinnias and gomphrena.

Care for Existing Blooms

• Deadhead regularly to encourage continuous blooms. Remove spent flowers from zinnias, salvia, coreopsis, gaillardia, marigold, and cosmos.
  → Read more about heat-loving flowers
• Remove spent winter annuals that are fading in the heat to make room for summer blooms.
• Mulch around flowers to help reduce soil temperature, retain moisture, and add organic matter to the soil.

Wildflowers

• Let wildflowers go to seed by leaving the plants in place. Shake them gently to drop seeds for next season.
  → Learn more about saving wildflower seeds

Planting Warm-Season Flowers

• Plant more warm-season annuals now, including sunflowers. I love this branching sunflower variety—it adds bright color and attracts birds. I plant it on the western edge of my garden to block late afternoon sun.
• Hollyhocks bloom from late April through June. Don’t forget to save the seeds! I gather them in a paper sack and let them dry through the summer. There are usually enough to share with friends or exchange at seed swaps.

Watering Guidelines for Flowers

• As heat increases, water annual flowers deeply every 2–5 days to a depth of 8–12 inches. Allow the top of the soil to dry between waterings to prevent rot.

Rose Care

My roses still usually look beautiful in May. If you give them some extra care, roses should continue blooming through early summer.

Ongoing Rose Care

• Don’t worry about leafcutter bees—the damage is only cosmetic and won’t harm your roses.
• Deadhead spent blooms regularly to keep flowers coming through early summer.
• Lightly fertilize roses this month to support continued growth and blooming. This is the rose fertilizer I use. As temperatures rise, lighter doses of liquid fertilizer are easier on your plants if you want to continue feeding them.

Refresh and Mulch

• If you’re growing alyssum around your roses, it may begin to fade in the heat. I let mine go as long as possible, then refresh the area once when the alyssum is done.
• To mulch your roses for summer, apply a 1-inch layer of compost around the base of the plant, then top it with 3 inches of wood chip mulch.
  • The compost feeds the soil and supports healthy microbial activity.
  • The wood chips help retain moisture, protect the soil surface, reduce evaporation, and keep the root zone as cool as possible in the summer heat.

Roses typically stop blooming in the extreme summer heat, but this mulch layer can help them survive and recover once temperatures cool again.

For a complete guide to helping your roses get through the summer, see this hot summer rose survival guide.

Fruit and Fruit Tree Care

May is an important month for fruit trees and berry plants in the low desert. Regular harvesting, careful watering, and a few key maintenance tasks can make a big difference in the health of your trees and the quality of your fruit as summer heat approaches. Here’s what to focus on this month.

Fertilize and Mulch

• Fertilize citrus trees this month. Water well before and after applying fertilizer. Use an organic citrus fertilizer or apply compost and worm castings using this method.
• Mulch around fruit trees with a 3–6 inch layer of organic mulch. Mulch helps lower soil temperatures, retain moisture, and improve soil health.
• I’ve started feeding my fruit trees regularly with Nutrient+ from Arizona Worm Farm and have been very pleased with the results. It’s especially helped my trees recover from summer stress and damage. This year, I’m applying it before the heat sets in—hoping it will help strengthen and prepare the trees for the intense summer ahead.

Harvest Time

• I love the fruit harvests in May. The strawberries, blackberries, and mulberries keep coming. Water strawberries consistently to prevent them from drying out.
• Depending on the varieties you’re growing you’ll often harvest peaches and apricots in May too. My Florida Prince usually gives me some ripe fruit this month. If birds start pecking the fruit, pick it slightly early and let it ripen on the counter. Learn more about growing peach trees here.

Herb Gardening

Warm temperatures in May bring a new burst of growth to many herbs. With a few simple tasks, you can keep your herb garden healthy and productive through the summer months.

Care for Existing Herbs

• I plant different varieties of basil all over my garden. I’ll put the smaller leaved varieties in places that get more sun and the larger leaf types in prime afternoon shade locations. Keep your basil cut back to encourage branching and nice full plants.
• Allow biennial herbs like dill, parsley, and cilantro to flower. Their flowers are so attractive to beneficial insects. If you look closely you may see all generations of ladybugs or other beneficials on your bolted herbs. This is one of my favorite things to point out to visitors in my garden during May. As seeds form, collect them in paper sacks once they begin to turn brown.
• Bay laurel grows well this time of year. Harvest bay leaves as needed.
• Lemon balm and other herbs from the mint family thrive in the warmer temperatures of May. By now, frost-damaged or woody growth pruned in March should be filling in with new growth. Enjoy the leaves! When it gets hot these herbs can struggle a little more. Make sure to move any container grown mint to a shadier location for the summer.
• Cut back spent lavender flowers to encourage more blooms. Bring the blooms indoors and enjoy the scent.
• Fertilize summer-growing herbs such as basil by adding a layer of compost.
• Apply mulch around the base of herbs to help retain moisture and regulate soil temperature. I use a thick 3-5 inch layer for the summer.
• Lightly prune borage after it has flowered to prevent excessive reseeding. You’ll probably still get lots of seedlings popping up, but they are easy to remove.

Watering Guidelines for Herbs

• Annual herbs will need more frequent watering as temperatures rise. Water to a depth of 8–12 inches every 2–5 days, allowing the top layer of soil to dry out between waterings.
• Desert-adapted perennial herbs, like rosemary, need deep but infrequent watering—about every 7–21 days, soaking to a depth of 18–24 inches.
• Mediterranean herbs such as sage, rosemary, lavender, oregano, and thyme are more likely to suffer from root rot due to overwatering than from drought stress. During summer, it’s especially important not to keep the soil too wet—let it dry out between waterings.

Landscape Plants

As the weather heats up, it’s still possible to plant summer-flowering shrubs and do some light maintenance in the landscape, but don’t be too aggressive this month. The heat is coming if it isn’t already here.

Planting and Spacing

• It’s okay to plant summer-flowering shrubs this month. Choose heat-adapted varieties and give each plant enough space to reach its mature size. I’m horrible at this and tend to overplant because there are so many plants I want to grow. Your landscape will look better if you can give each plant enough room.
• Don’t shear shrubs into shapes! Not only does this look horrible, but it reduces blooms and the life of the plant. You’re cutting off the energy the plant needs to survive summer.

Pruning Guidelines

• Don’t prune newly planted trees or shrubs. Let them get established first.
• Lightly prune dead or damaged branches on mature trees and shrubs as needed.
• Save any heavy pruning for later in the fall when temperatures have cooled.
• Trim spent blooms on spring-flowering perennials like Texas mountain laurel and penstemon to keep plants tidy.

Mulching

• Apply a 3–6 inch layer of mulch around the base of trees and shrubs to reduce soil temperatures, retain moisture, and improve soil structure over time.

Landscape Watering Guidelines:

• Water desert-adapted trees, shrubs & vines every 7-21 days (Water to a depth of 24-36″ trees / 18-24″ shrubs / 8-12″ vines).
• Water high water use trees every 7-10 days (Water to a depth of 18-24″).
• Water high water use shrubs every 5-7 days (Water to a depth of 8-12″).
• Water high water use vines every 2-5 days (Water to a depth of 8-12″).

If you’re new to gardening—or just curious about what gardening blogs mean when they mention pruning, mulching, or perennial—check out my Gardening Glossary. It’s a simple reference that helps make all the terminology clear so you can follow posts with confidence.

Ready for More?

More Resources

• Arizona Vegetable Planting Guide helps you learn when to plant vegetables in Arizona and whether to plant seeds or transplants.
• Arizona annual flowers planting guide helps you learn when to plant flowers in Arizona and whether to plant seeds or transplants.
• Would you like more information about gardening in Arizona? This blog post shares 7 tips for growing a vegetable garden in Arizona. 
• Arizona Herb Planting Guide features pictures and planting dates for nearly 40 herbs that thrive in the low desert of Arizona.

Gardening Classes

Ready to grow your skills? Sign up for one of my gardening classes taught in person and online at Growing in the Garden Academy. These seasonal classes are designed to help gardeners of all levels succeed, with practical tips and techniques tailored to desert gardening. Visit Patreon to start learning today, and don’t miss my classes tailored specifically to spring and summer gardening: Spring Sprint: Maximizing Warm-Season Harvests in the Low Desert and Beating the Heat: Essential Practices for Low Desert Summer Gardening.