Plant blood orange, grapefruit, kumquat, lemon, mandarin, orange, pummelo, and tangelo in Sunset climate zones 12 and 13. Grow 'Bearss' lime, 'Improved Meyer' lemon, or 'Mexican' thornless lime in a large container and move it indoors before winter arrives in zones 1a-3b, 10-11.
Set out seedlings of anise hyssop, basil, bay laurel, chives, lemon grass, mint, oregano, rosemary, sage, salad burnet, and thyme. One good source is Companion Plants.
If you like the bold flowers of tropical hibiscus (Hibiscus rosa-sinensis), the exceptional colors and denser foliage of two new ones will thrill you. 'Cool Wind' stays a petite 2 to 3 feet tall, is great for patios and pots, and produces huge numbers of white flowers with pink centers. 'Starry Wind' grows 5 to 10 feet tall and produces dozens of orange-red flowers. Both thrive in full sun and are hardy to 32° (protect during cold snaps).
Three native species to look for are Wright's milkpea (Galactia wrightii), a delicate vine with pink flowers; Guardiola platyphylla, a sunflower relative that attracts butterflies and birds; and Mexican passionflower (Passiflora mexicana), a vigorous vine with unusual green flowers that have rings of red filaments that fade to pale violet.
Set out transplants of broccoli, cabbage, chard, and kale in zones 1a-3b. Sow seeds of beets, carrots, salad greens, and spinach. Set out transplants of eggplant, peppers, and tomatoes in zone 10. Sow seeds of beans, cucumbers, melons, and squash. Set out transplants of eggplant, peppers, and tomatoes in zones 11-13. Sow seeds of beans, carrots, corn, cucumbers, melons, and squash. One good seed source is Plants of the Southwest.
Grow Penstemons in zones 2b, 3a, and 10–13. These beautiful, water-thrifty perennials draw hummingbirds. Try P. ambiguus, P. barbatus, P. eatonii, P. pinifolius, and P. strictus; all are available from Plants of the Southwest.
Try a new agave in zones 12–13: Plant striking ‘Blue Glow’ (A. attenuata x A. ocahui ‘Blue Glow’), which has deep blue-green leaves with maroon leaf margins, is hardy to 15°, and forms a 3- by 3-foot rosette. Find it at B&B Cactus Farm in Tucson (bbcactus.com).
Check out Wildflowers of Tucson or Chihuahuan Desert Plants for close-up photos and detailed information about wildflowers that grow throughout the Southwest. Bloom time varies from spring through fall.
Adjust irrigation timers. As temperatures increase, so do the water needs of your garden. To give plants just the right amount, adjust the timer by increasing the number of days per week it operates, but not the number of minutes per cycle.
Feed established plants (including roses) and lawns with a balanced fertilizer. Feed palms with a fertilizer formulated specifically for them. To avoid burning roots, water thoroughly before and after applications.
Control flea beetles. These small hard-shell insects produce tiny holes in the foliage and flowers of Mexican evening primrose and other leafy plants. To treat, spray plants with insecticidal soap twice daily until damage abates.
Spread a 3- to 4-inch layer of compost, bark chips, forest mulch, or other organic matter around plants to help retain soil moisture and keep it cooler. Organic matter also benefits the soil as it breaks down.