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April 2014 Gardening Checklist for Arizona’s Low, Mid and High Elevation

Author: Cathy Cromell
Issue: April, 2014, Page 116
verde blooms

Celebrate Arbor Day by planting a palo verde, Arizona’s state tree, and enjoy its brilliant cloud of yellow blossoms each spring. In Spanish, palo verde means “green stick,” referring to the tree’s unusual green bark. In times of severe drought or cold, palo verdes can drop all their leaves, and the green bark will continue photosynthesis, a nifty trick that creates a remarkably drought-tolerant tree.

Blue palo verde (Parkinsonia florida), the official state tree, has bluish-green bark and grows 30 feet tall and wide. Another native, foothills palo verde (P. microphylla), grows 15 feet tall and wide and is better suited to small yards. Both are cold hardy to 15 degrees F. Palo brea (P. praecox), with lime-green bark and an umbrella shape reaching 25 feet tall and wide, is native to northern Mexico and South America. It is cold hardy to 20 to 25 degrees F. Thornless hybrids are also available.

Arizona’s Low Desert
Landscape plants—Continue transplanting desert-adapted trees, shrubs, groundcovers, vines, ornamental grasses, perennials, cacti and succulents. The earlier in the month they are planted, the better, giving roots time to establish before summer’s stressful heat arrives.

Citrus trees—Add varieties that ripen at different times, to extend the harvest period. If space is limited, a single “cocktail” tree—which has several varieties grafted onto one rootstock—might be a good choice.

Container-grown roses—Choose a planting site that receives about six hours of full sun daily. An eastern exposure with morning sun and protection from hot afternoon sun is best. Avoid areas with western exposures against walls. Dig a hole 12 to 18 inches deep and 18 to 24 inches in diameter.

Herbs—Transplant warm-season favorites, including basil, lavender, rosemary, sage and scented geranium.

Warm-season veggies—Sow seeds for black-eyed peas, cantaloupe, cucumbers, jicama, lima beans, okra, peanuts and summer squashes, such as crookneck, pattypan and zucchini.

Photos - From left: Okra • Rhubarb

Arizona’s Low Desert
Control grapeleaf skeletonizers—Adult bluish-black moths lay eggs on grapevines in spring. When caterpillars hatch, they begin feeding voraciously, moving in groups and leaving behind “skeletonized” foliage. Regularly examine the undersides of leaves and along stems, and hand-pick these colorful yellow, blue and black-striped caterpillars. Wear gloves and a dust mask when handling, as they have stinging spines that can irritate skin and also can become airborne and be inhaled.

Allow wildflowers to go to seed—They will self-sow for next year, or you can collect the seeds and store them until fall to spread elsewhere. If a neighbor or homeowners’ association complains about the “dry weeds,” politely explain the value of native wildflowers for birds and pollinators and offer to share seeds. As seeds begin to dry and drop on their own, they are ready to collect.

Arizona’s mid elevations
Thin deciduous fruit—Apple, apricot, peach and pear trees set more fruit than they can bear to maturity. To inhibit branch breakage due to excess weight and improve ultimate fruit size, thin to 6-inch spacing between fruit.

Arizona’s high elevations
Prepare for spring—As temperatures warm, gradually remove all but 3 to 4 inches of protective winter mulch around landscape plants. Left in place, it prevents sunlight from reaching buds and keeps plants in a dormant state.

Arizona's High Desert
Rhubarb—This perennial crop needs winter temperatures below 40 degrees F and summer temperatures averaging less that 75 degrees F; thus it is not suited to warmer microclimates. Because rhubarb will grow and spread year after year, ensure that its sunny planting site offers good drainage and organically rich soil. Spread 6 inches of organic matter (compost, aged manure, dried leaves, grass clippings) on top of the planting area and turn it under to a depth of 12 inches. Plant rhubarb root crowns 2 inches deep and allow 1 square yard of space per plant. Feed with fertilizer that is higher in phosphorus and potassium than nitrogen, such as 5-10-10; then water deeply. Do not harvest during the first year, and cut just a few stalks in the second year, which allows the plant to develop a strong root system. Eat rhubarb stalks only; leaves contain toxic oxalic acid.

Hummingbird mints—Also called licorice mint or giant hyssop, these herbaceous perennials (Agastache sp.) are available in varied hues, including blues and purples, pinks and roses, and oranges and reds. Most species are native to Arizona, New Mexico, Texas or Mexico and thrive in low-water-use landscapes. Their minty or anise fragrances deter deer and rabbits. Bloom periods vary from early summer to mid fall. Plant several with staggered flower times to provide nectar for many months. Over the years, Phoenix Home & Garden Master of the Southwest David Salman has selected an array of these plants for exceptional color and adaptability. Check them out at

Cathy Cromell is a Master Gardener and co-author of Earth-Friendly Desert Gardening (Arizona Master Gardener Press).
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