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May Garden Checklist

Learn what to plant this month, get maintenance advice and troubleshoot your gardening challenges with an expert.

By Kelly Young

What to Plant

Low Elevations

Cacti and succulents—Group these easy-care plants in clusters so they are more visible in the landscape. The compass barrel cacti (Ferocactus cylindraceus) only grows to approximately 1.5 feet wide and looks great planted in a row in narrow spaces. Cacti and other succulents can sunburn in direct light, so plant them where they will receive afternoon shade or protect them with shade cloth for the first few summers.

Trees and shrubs—Look for indigenous Sonoran Desert plants at the nursery for late spring planting. Native plants generally survive May temperatures better than non-native counterparts. Foothills palo verde (Parkinsonia microphylla) is a compact tree with lacy, yellow-green foliage that does well with very little water or maintenance.

Warm-season vegetables—Sow seeds of yard-long beans, also called asparagus beans. Train these vines to grow on a trellis to maximize garden space, and harvest pods while they are still green and tender for optimum sweetness. Plant sweet potato slips in an area where they have plenty of room to spread out.

Sunflowers—Sunflowers provide food and refuge for beneficial insects, including pollinators. Sow seeds in loosened soil to ease germination. To keep hungry birds from digging up the seeds, screen the ground with floating row covers, available at nursery centers, until new plants produce two or three leaves.

Basil—Plant transplants of this heat-loving summer staple in full sun. 

What to Plant: Middle Elevations

Vegetables—Sow snap peas, arugula, kale, lettuce, spinach and other leafy greens from seed. If you like horseradish, you can find fresh roots at the grocery store to plant, or order crowns from an online source, such as Gurney’s Seeds and Nursery ( or Burpee Seeds and Plants (

Flowers—Sow seeds of cosmos, marigolds, petunias, sweet peas and zinnias. Plant taller varieties in the back and shorter types in the foreground so you can see and enjoy all of the blooms.

Landscape Plants—Transplant native or regionally adapted ornamental trees, shrubs, vines and perennial grasses into locations that provide enough room for them to reach their mature size without interfering with sidewalks, buildings or other structures. 

High Elevations

Vegetables—Transplant seedlings you started indoors during February and March. Tomatoes can be transplanted later in the month, but make sure to cover them with frost cloth on evenings when temperatures are expected to dip below freezing.

Landscape trees, shrubs and vines—When selecting plants at your local nursery, look for healthy specimens that are actively growing and pushing out new leaves. Be vigilant about not bringing unwanted pests home from the nursery, and avoid purchasing plants that share their container with weeds.


Low Desert and Middle Elevations

Mulch around trees and shrubs—Conserve soil moisture by placing a 3- to 4-inch layer of coarse mulch around landscape plants. Avoid letting mulch rest against trunks, as it can act as a conduit for pests.

Scout for spider mitesJuniper, arborvitae and pyracantha are susceptible to spider mites, which are tiny eight-legged pests that feed on plant juices and can lead to the decline and death of the plant. Look for the telltale weblike material and sticky mess they leave behind and promptly wash any remaining off with a strong stream of water.

Low Desert

Harvest winter vegetables—Pluck carrots, beets and radishes that have not already gone to seed. Cull leafy greens that taste bitter or are riddled with pests.

Adjust irrigation—Plant water demands will continue to increase for a few more months. To determine how much water to apply to your landscape, visit the Arizona Municipal Water User’s Association’s site “Watering Schedules Tailored for Landscapes in the Sonoran Desert” at

Middle Elevations

Fertilize—For a lush, green lawn, give turfgrass 2.5 pounds of ammonium sulfate per 1,000 square feet of lawn, which provides 0.5 pound of actual nitrogen. Feed roses and other flowering shrubs with a complete fertilizer and follow the product label to determine the correct amount to apply.

High Elevations

Prune—Once flowering shrubs have finished their spring bloom, cut stems back to their point of attachment to reduce plant size.

Pro Tip: Protecting Fruit

By Bruce Solomon, customer care representative, Arcadia Color Garden, Phoenix

Fruit on deciduous trees, such as peaches, nectarines, apricots, plums, figs, apples, grapes and berries, is appealing to hungry birds and insects. To prevent unwanted visitors from devouring your harvest, try these tips: 

As fruit comes up to size—but before it ripens—cover trees and plants with bird netting. On smaller plants, support the covering above with stakes, so that birds cannot sit on the netting and reach the fruit. On trees, secure the netting to the trunk or bring it to the ground and weight it with bricks to prevent birds from becoming trapped beneath the canopy.

Create a scarecrow device—something that moves and sparkles to frighten would-be fly-in diners. Holographic bird scare tape, which can be purchased online or at your local nursery, or strips of aluminum foil can be tied to branches. Fruit can also be covered with paper bags secured with twist ties, which also discourages fruit beetles.

If ants attack, try wrapping tree trunks with duct tape (sticky side facing out) or a strip of aluminum foil coated with petroleum jelly or Tanglefoot, an environmentally friendly insect repellant. Diatomaceous earth can also be effective when applied to the ground around the base of tree trunks to thwart crawling insects.

Garden Solutions

How can I tell when eggplant is ready to harvest? The plants I put in in March are already bursting with fruit.

Eggplants are ready to harvest when the skin is shiny. Young, small fruits tend to have better flavor and texture. If you leave them on the plant for too long, the skin tends to become tough and the flesh gets bitter. Frequent harvesting will encourage your plants to continue blooming and producing fruits.

An arborist said I need to excavate the soil around my 20-year-old eucalyptus, which is 50 feet tall. I love the tree and the shade it provides, but I have never heard of such a procedure, and the price quoted was very high. Is this necessary?

The root collar, or region of the trunk where the roots meet the stem, is prone to damage when buried. It should be visible above ground and flare out with a pyramidal shape. When trees are planted too deeply, mulch is often applied against the trunk or soil accumulates over time around the collar, burying the flare and frequently leading to the decline and eventual death of the tree. Removing soil to expose the flare is an effective but expensive procedure to save the tree. Weigh the cost of excavating the soil against the reduction in cooling costs the tree offers—or the potential costs of the tree dying, falling and damaging property.

I work long days and only get out into the garden at night.  Unfortunately, mosquitoes chase me indoors most evenings. I’d like to try burning citronella candles to repel them. Are they effective?

Unfortunately, citronella candles are not effective in protecting against being bitten by mosquitos. Research has shown that the best approach to keeping these pesky insects at bay is three-pronged: 

  • Make your yard inhospitable to mosquitoes. Mosquitoes reproduce in standing water, and some species can survive in moist soils. Dump any water that has accumulated in pots or toys, and remove anything that can trap rainwater or sprinkler overspray. Adjust irrigation so the soil surface dries out between watering. Report stagnant or algae-ridden pools to your county health department. 
  • Keep skin covered and treat clothing with products containing the active ingredient permethrin. 
  • Protect uncovered skin with DEET or oil of lemon eucalyptus (not lemon eucalyptus essential oil, which is not as effective). Go to to learn more about preventing mosquito bites at home.


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