September Gardening
What to plant in July
- Warm-season cacti and succulents
- Provide afternoon shade or a piece of shadecloth on the plant’s south- and west-facing sides for the first summer to keep them from sunburning as they get established
- Annual seed: cosmos, globe amaranth, lisianthus, marigold, and sunflower
- Annuals: Arizona poppy, cosmos, coyote gourd, globe amaranth, lisianthus, marigold, sunflower, vinca, and portulaca
- Palm trees
- Water newly planted palms daily for 3 days, then weekly for the first 3 weeks, then every other week through the remainder of the summer heat
- Tropical, heat-loving trees
- Veggies (after mid-month): Armenian cucumbers, black-eyed peas, bush beans, corn, melon, pinto beans, pumpkin, and winter squash
- You can also set out pepper and tomato transplants for a fall crop in the cooler areas of our zone, or start seed indoors if you live in a warmer part of the region
What NOT to plant in July
- Fruit trees
- Any species that is summer dormant, fall is a much better time to plant many of these species (when their roots will be actively growing and they are able to get established).
What to Fertilize
- Potted annuals: once this month with a water-soluble plant food
- Summer-growing bulbs in containers: once this month with a water-soluble plant food
- Warm-season succulents and cacti in containers: once this month with a low-nitrogen water-soluble plant food mixed at half of the recommended strength for houseplants.
- Augustine lawn
- Bermuda or hybrid bermuda lawns: continue your regular fertilization schedule (monthly, every six weeks, or 4 times a year)
- Potted perennials: every other week, and
- Potted shrubs: once this month.
- Summer-flowering shrubs in the ground: feed lightly (1/2 strength) once this month
- hold off on feeding other garden plants that aren’t flowering or growing this time of year.
- Palms: once this month with a food formulated for palm trees
- Water deeply before and after applying fertilizer
- If you live in a cooler area of our zone you can fertilize actively growing veggies and herbs once this month with a side dressing of compost or a balanced, complete fertilizer.
- Don’t fertilize if you live in a warmer area of the zone and plants are not actively growing.
What to NOT Fertilize
- Don’t fertilize fruit trees this month
- Anything that is dormant and not actively growing
Prune, Divide, and Conquer
- Deadhead annuals and summer-flowering perennials and shrubs regularly to keep them blooming
- Don’t remove yellowing leaves from iris – let them remain on the plant until the leaves dry up and die completely
- Don’t prune fruit trees this month
- Dethatch bermuda lawns if the thatch layer is thicker than ½”
- Give your lawn a good drink of water and a dose of fertilizer after dethatching
- Continue deadheading to promote more blooms on your summer flowering perennials.
- Thin the crowns of fast-growing desert-adapted trees that have become overgrown to keep them from catching too much wind and breaking or blowing over in monsoon storms
For the Fruits and Veggies
- Clean up fruit that has fallen around the base of your trees (or fruit that is damaged but still hanging on the tree) to keep from attracting foraging insects that will destroy the fruit before it’s ready to be picked.
- If you live in a cooler area of our zone you can fertilize actively growing veggies and herbs once this month with a side dressing of compost or a balanced, complete fertilizer. Don’t fertilize if you live in a warmer area of the zone and plants are not actively growing.
- Don’t prune fruit trees this month
For the Lawn
- This is the last month to plant warm season lawn grasses
- Water lawn grasses every 3-4 days to a depth of 8-10 inches
- You can skip a watering if we get ½“ of rain or more
- Feed St. Augustine lawn, and continue your regular fertilization schedule with bermuda or hybrid bermuda lawns (monthly, every six weeks, or 4 times a year)
- Dethatch bermuda lawns if the thatch layer is thicker than ½”
- Give your lawn a good drink of water and a dose of fertilizer after dethatching
- Continue a regular mowing schedule to keep your lawn at the proper height (Copy mowing heights from June’s post)
- Change the mowing direction each time you mow, starting at different parts of the lawn each time to avoid rutting or compacting the soil.
- Never mow a wet lawn, wait for the blades and the top layer of soil to dry before performing this chore
Water Wisely
- Large columnar cactus, ocotillos, and large yuccas: once this month to a depth of 3 feet
- Containerized plants: daily, sometimes twice daily if we experience excessive heat or high winds
- Annuals in the ground: to a depth of 6-12 inches every 2-3 days
- You can skip watering annuals if we get ½ an inch or more of rain
- Summer-growing bulbs: weekly to a depth of 6 inches
- Smaller cacti, agaves, and yuccas: once this month to a depth of 2 feet
- Lawn grasses: every 3-4 days to a depth of 8-10 inches
- You can skip a watering if we get ½“ of rain or more
- Roses: to a depth of 16-18 inches every 3-5 days
- Shrubs: every 5-8 days to a depth of 2 feet
- Established desert-adapted trees: once this month to a depth of 3 feet
- If your house gets ½” of rainfall or more you can skip this watering
- Non-desert-adapted trees: twice this month to a depth of 3 feet
- If your house gets 1” of rainfall or more you can skip this watering
- If the edges of your leaves are turning brown despite getting plenty of water, this may be an indication of salt buildup in the soil. Apply water more deeply than you usually do to wash salts away from the root zone, and make sure that fertilizers are always applied at the recommended rates.
- Avoid overwatering cacti, succulents, penstemon, milkweed, brittlebush and other drought-tolerant perennials, and drought tolerant herbs such as rosemary, lavender, salvia, and thyme. The roots of these plants are prone to rotting when warm soil stays too wet for too long
- If your plants are looking thirsty, resist the urge to water lightly but more frequently. It’s OK to step up the frequency if your plants need more water, but make sure that you’re watering to the proper depth every time.
- Water in the early morning hours – daytime watering in the heat is inefficient, and watering in the evening hours can encourage fungal growth
General Chores
- Watch leaves for powdery mildew as humidity increases
- Water plants at the ground level to prevent splashing water that can spread mildew spores
- Remove fallen leaves from the base of the plant as soon as possible, and remove symptomatic leaves from the plant if only a small percentage of the leaves are affected
- Remove plants that are heavily affected, or treat with a fungicide that kills powdery mildew
- Watch for cochineal scale to begin appearing on chollas and prickly pears. These tiny insects have a white, fuzzy covering that looks something like a fungus growing on the plant. You can read more about this interesting insect and how to control it here.
- Mushrooms may appear in lawns and in the soil around the bases of plants this time of year. In general, most of these fungi are harmless to the plants, and are merely an indication that there’s more moisture in the soil than usual. They can be removed by hand (wearing a pair of gloves) if you find them bothersome, but they’ll likely be gone in a few weeks if left alone.
- Give your glossy-leaved plants a shower every couple of days to wash away dust that attracts and harbors spider mites.
Sources: University of Arizona online publications, Arizona State University online publications, Desert Botanical Garden website, Tucson Botanical Garden website, Gardening in the Deserts of Arizona by Mary Irish, Arizona Master Gardener Manual
