May Gardening Tips for the Desert Southwest

Enjoy the garden this month -- before summer heat arrives. Use our checklist to make the most of your gardening hours.


Get Planting
  • Annuals, perennials, shrubs, and trees can all go in the ground this month. Purchase container or balled-and-burlapped plants.
  • Attract butterflies by planting chaste tree (Vitex), oleander (Nerium), Texas sage (Leucophyllum frutescens), or butterfly bush (Buddleja).
  • For trees, consider mesquite, desert willow (Chilopsis linearis), palo verde (Parkinsonia), Chinese pistache (Pistacia chinensis), or live oak (Quercus).
Add Summer Color
Red yucca

Tuck gladiolus corms into the ground at two-week intervals to ensure a long season of continuous bloom.

Add cannas to your garden to savor striking foliage. Look for solid green or burgundy foliage, or try one of these colorful cultivars:

'Pretoria', which offers leaves striped with green and creamy-yellow

Tropicanna, which has vibrant stripes of chartreuse, pink, yellow, gold, red, and green on the foliage

'Stuttgart', which bears white blotches and edges on otherwise solid green leaves

These are all eye-catching underplanted with asparagus fern and/or sweet potato vines.

Test Garden Tip: Plant drought-tolerant red yucca (Hesperaloe parviflora). Its blooms stage a summer-long flower show that beckons butterflies and hummingbirds.

Plan to Water

May in the Southwest brings hot, dry, and often windy conditions to the garden. Rainfall is typically scarce, which makes watering a key task.

Don't forget to irrigate newly planted drought-tolerant or xeriscape plants. The secret to a long-term, low-water-use disposition is firm establishment, which means watering frequently and deeply the first year after planting.

Water crape myrtles regularly once flower buds form. You will likely need to add a soil-acidifying product with fertilizer this month.

Mulching

Get mulch in place. Aim for a 2- to 3-inch layer to insulate soil from temperature extremes, slow water loss, and smother weeds.

Test Garden Tip: Inspect irrigation systems. Replace broken heads or lines; readjust sprinkler heads as needed. Double-check hoses and nozzles; replace leaky washers or hose ends.

Fertilizing

Fertilize landscape plants, including roses, fruit trees, and vegetables. At higher elevations, don't feed plants that haven't yet awakened from dormancy.

Feed citrus late this month, except for newly planted trees. Also: Don't fertilize these for the first year while they get established. Use a specialized citrus fertilizer, which contains the micronutrients iron, zinc, and manganese. If you choose an organic citrus fertilizer, read the label to be sure it includes micronutrients. If not, apply seaweed fertilizer to supply the missing minerals.

Fertilize lawns this month. At high elevations, feed tall fescue, bluegrass, and perennial ryegrass. In desert and low elevations, feed St. Augustine lawns. Check with a local garden center or extension office to confirm fertilization rates.

Test Garden Tip: Feed Mexican elders (Sambucus mexicana) now before they enter summer dormancy to minimize poor summer appearance. Use an all-purpose landscape fertilizer containing iron and sulfur.

Pruning

It's okay to prune spring-flowering shrubs as blooms start to fade. Don't prune desert legumes, like palo verde (Parkinsonia) and mesquite (Prosopis), except to remove dead limbs. Pruning to shape these trees is best done in late summer.

Houseplants

Shift houseplants outdoors when night temperatures remain above 65F. Tuck these plants into a shady spot and fertilize with an all-purpose fertilizer to jump-start growth. You can also remove the top inch or two of soil and add a layer of compost to boost growth.

Landscape plants such as bird-of-paradise, lantana, and oleander may suffer winter damage and emerge late in spring. If you watered infrequently during the winter, these beauties will likely return. Be patient with them and take care not to remove them prematurely.

The Vegetable Garden in May

Warm-season veggies can go in the ground this month, including sweet potato, okra, melon, and black-eyed peas. Other heat-loving favorites, like tomatoes, eggplants, peppers, corn, and squash, can also go into the garden.

Planting dates vary based on your elevation. Lower desert locations can plant early in the month; higher elevations should wait until month's end. Check with a local garden center or extension office for ideal timing.

The Flower Garden in May

Get heat-loving annuals (ageratum, zinnia, celosia, marigold, cosmos, salvia) in the garden as soon as seedlings are for sale. At highest elevations, delay planting until all danger of frost is past.

Pinch flower buds on annual seedlings to encourage young plants to direct energy to root growth. Remove growing tips to promote bushiness.

Be sure to deadhead, or cut the faded flowers, off your plants. Deadheading helps many varieties rebloom as they're not putting energy into making seed.


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