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April 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 


All Elevations

Trees can add value to your home and reduce cooling costs in summer. 

Celebrate National Arbor Day on April 26 by planting a tree. Consult your local nursery for guidance on the best choice for your landscape and elevation. 

Low Elevations

Warm-season vegetables—Try heat-loving leafy greens such as Malabar spinach (Basella spp.) or molokhia (Corchorus olitorius) for something out of the ordinary. Sow seeds of okra; melons; cucumbers; lima, bush and yard-long beans; and black-eyed peas. Go with transplants for peppers, eggplant and tomatillo, as they will bloom sooner than those started from seed.

Landscape plants—Plant cacti, trees, shrubs, vines and ornamental grasses before summer heat sets in. Dig the planting hole at least twice as wide but no deeper than the rootball. Plants installed too deeply are prone to disease and root damage. 

Flowers—Dazzle the neighbors with a variety of sunflowers, lisianthus, marigolds, cosmos, four o’clocks and blanketflower. Seed the tallest varieties in the background to ensure that the shorter counterparts aren’t obscured from view.

Arizona’s Middle Elevations

Cool nights and longer, warmer days make this a great time of year for planting ornamental trees, shrubs, vines and perennial grasses.

Vegetables—Plant perennial asparagus crowns in a sunny location where they can grow undisturbed year after year. Sow seeds of chard, kale, lettuce, mustard greens, and snow and sugar snap peas directly into the soil. Transplant or sow broccoli seeds, allowing for at least 2 feet between plants to give them space to grow to their full size. Put out garlic and onions from sets in soil that has not been amended with sulfur, which can make them taste unappealing for most palates.

Herbs—Chives, dill, parsley, chamomile and cilantro seeds germinate rapidly in the spring. Stick with transplants for oregano, thyme, mint and marjoram, which tend to be more difficult to start from seed. Plant them in beds in close proximity to the kitchen so  that they’re easily accessible. 

Bulbs—Plant summer-blooming dahlia, gladiolus, caladium, allum, canna and crinum bulbs in soil amended with a phosphorus fertilizer, such as bone or fish meal, which promotes large, luxurious flowers.

Arizona’s High Elevations

Landscape plants—Plant ornamental trees, shrubs, vines and perennial grasses now, but cover them  when temperatures dip below freezing.

Vegetables—Get a head start on summer planting by starting cabbage, kale, tomato and pepper seeds indoors.

Maintenance


All Elevations

Inspect irrigation systems—Check for and remove any blockages in drip systems. Replace emitters that aren’t working properly. Adjust the timer to water more frequently as the daytime temperatures climb. 

Increase irrigationIncrease the frequency of watering to accommodate warmer days. The frequency is determined by your soil and plant types. 

Scout for pests—Early detection and removal is the best way to get out ahead of pests, including weeds, in the garden and landscape. Look for newly emerged weed seeds around irrigation emitters. Search for clusters of insect eggs on the underside of leaves and remove them by hand. 

Mulch—Lay wood chips 3 to 4 inches deep below the soil surface to suppress weeds and conserve soil moisture. Many tree companies will provide wood chips free of charge.

Arizona’s Low Elevations

Prune—If your shrubs have been sheared repeatedly throughout the years, restore their natural shape with rejuvenation pruning this month. Cut shrubs to approximately 8 to 10 inches tall. Always follow up with a deep irrigation to support new shoots.

Protect young fruit trees from sun—Citrus and deciduous fruit trees with thin bark are prone to sunburn. Loosely wrap young trunks with shade cloth or paint them with white latex paint diluted with equal parts water.

Arizona’s Middle Elevations

Thin deciduous fruits and  vegetable seedlings—Give apples, peaches, pears, apricots and other tree fruits space to develop. Leave only one fruit per flower cluster and one fruit per fist-length of stem. Refer to the vegetable seed packet for the optimal planting space and thin accordingly. Use the culled seedlings in salads; they’re delicious.

Arizona’s High Elevations

Fertilize—New spring growth will benefit from a boost of nutrients. Apply ammonium phosphate (16-20-0) around the dripline of deciduous plants and follow with water to enable absorption by roots. Use 1 pound for every 5 feet of canopy diameter. Apply one-half that rate for ornamentals.

Cover frost-sensitive plants—April can still be chilly enough to cause damage to recently installed plants. Cover with a cotton sheet or frost cloth designed for this purpose when temps dip below
32 degrees.

PRO TIP: POLLINATOR-FRIENDLY PLANTS


By Jackie Lyle, certified arborist and Master Gardener, Civano Growers, Tucson

  • To grow a successful produce garden, attracting pollinators—including hummingbirds, bees, moths and butterflies—is essential. Many summer vegetables, such as melon, squash and tomatoes, require cross-pollination, without which the plants will flower but not set fruit. When the pollinator transfers pollen grains from the male anther of one flower to the female stigma of another, fertilization occurs and fruit are created. Having this micro-ecosystem ensures a healthy garden and a generous crop. 
  • To lure pollinators to your garden, I recommend the drought-tolerant Monarch Magnet (Asclepias linaria ‘Monarch Magnet’), a compact species of milkweed that thrives in full sun and does well in containers. Reaching a mature height and width of 2 to 3 feet, this shrub’s clusters of bright white blooms are a feast for pollinators.  
  • For more information, visit www.fs.fed.us/wildflowers/pollinators/What_is_Pollination.

Garden Solutions


Some of my jade plant’s leaves recently developed brown, rough patches. It never had this problem until I moved it to the windowsill near my African violets. Were the leaves sunburned?

Are the damaged leaves on the side of the plant that faces the window? If so, the leaves are probably sunburned. Even succulents such as jade plants can suffer from sunburn when suddenly exposed to bright, direct light. If your plant was previously growing in a darker location in the house, the sudden change may have led to the damage. Return the plant to where it was or move it to an area where it will receive more filtered or indirect light. Remove the sunburned leaves if you find them unsightly.

How much should I water the Cara Cara navel orange tree I planted in January? It’s hard to find a resource that tells me the exact amount it needs.

There is no simple answer to this simple question. The amount and frequency of irrigation depends on a number of factors.  Water more often in sandy soils, areas with minimal ground cover and during hot, dry, sunny or windy weather.  Trees and shrubs require more frequent irrigation during their first few years after planting to support roots as they colonize the soil in their new habitat. Taper off the frequency as the tree grows and the weather cools. Apply water at the dripline of the tree and deeply enough to wet the entire root ball.  A thick (3- to 5-inch) layer of mulch will keep the soil cooler and slow evaporation. For more information, check out “Watering Trees and Shrubs” offered by the University of Arizona at extension.arizona.edu.

The radishes in our school garden never seem to get any larger than the diameter of a pencil. Do they need more fertilizer?

There are a few reasons why radishes don’t grow as plump as we want them to. The most likely explanation is that they are crowded. Radishes should be planted at least 2 inches apart in order to reach a harvestable size. Check the spacing between your plants, and thin them out if they are crowded. Hard, compacted soil can also restrict root growth.  If this is the case in your garden, you may need to work more organic matter and gypsum into the soil before planting again. Finally, excess nitrogen fertilizer can cause the radish tops to grow big and green while the roots stay small.  Adding more fertilizer will not solve the problem and will likely only make it worse.

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