August Gardening
The number of the month is 100! Things really start changing in the gardens of Tucson once our temperatures permanently drop below this number, which should be happening soon. Get ready to let the dirt fly with Civano Nursery’s guide to September gardening in the low desert!
What to Plant in September
- Cool-season annual seeds: aster, columbine, hollyhock, statice, and yarrow can be planted indoors and transplanted into the garden when they’re ready in November
- Cool-season annuals: bachelor’s buttons, lobelia, pansy, petunia, snapdragon, stock, and sweet alyssum can be planted once the temperatures are steady below 100° F
- Winter veggie seeds: snap beans, beets, bok choy, Brussels sprouts, cabbage, carrot, celery, collard greens, cucumber, endive, fennel, kohlrabi, leek, lettuce, mustard greens, peas, radish, spinach, Swiss chard, turnips
- Winter veggies: broccoli, Brussels sprouts, cauliflower, and potatoes. Plant garlic, and onions later in the month once temperatures have cooled.
- Strawberries!
- After you see new growth on your newly planted strawberries, feed them with a balanced, water-soluble fertilizer mixed at a low concentration
- Herb seeds: once temperatures drop below 100°F sow seeds of anise, salad burnet, calendula, chamomile, chervil, cilantro, cumin, dill, fennel, parsley, and sorrel.
- Herbs: sweet bay, chives, lavender, marjoram, rosemary, sage, and thyme
- Warm-season succulents, cacti, agave and yuccas
- Containerized roses in the ground or in new containers
- Cold-hardy, woody shrubs after temperatures have dropped below 100°F
- Water every 2-3 days for the first 2 weeks, then slow begin extending the time between water applications until you’re watering every 2 weeks through winter, making sure that you’re watering to a depth of 2 feet to encourage deep rooting
- Cold-hardy trees that aren’t deciduous
- Water daily for 3 days, then begin to gently stretch the time between water applications until you’re watering every 2 weeks
- If possible wait until winter to plant deciduous trees
- Ornamental grasses
- Spring-flowering perennials
- Winter-growing bulbs: plant when temperatures have dropped below 100°F
- Water freshly-planted bulbs every 2 weeks until you see new growth, then water weekly through the remainder of the warm weather
- Containerized bulbs should be watered every 7-10 days until you see new growth, and then watered when the top inch of the soil is dry
What NOT to Plant in September
- If you purchase a bulb that is blooming, let it spend the next year in the container that it was purchased in, and wait to plant it next fall
- Deciduous trees (including deciduous fruit trees): They can technically be planted any time of year in our area, but they do best if planted when they’re dormant
What to Fertilize
- Annuals: Feed once after they’ve been in the ground for at least 2 weeks, and are showing signs of new growth
- Containerized bulbs (that are actively growing): feed once or twice with a water-soluble fertilizer
- Grapes: last fertilizer application for the year
- Bermuda lawn: feed once with a balanced fertilizer that is high in potassium and phosphorus
- Unless you’re overseeding, this will be the last feeding your Bermuda lawn will need until it starts growing again next spring
- Zoysia or St. Augustine lawn: feed once this month
- this will be the last feeding your lawn will need until it shows new growth again next spring
- Summer-flowering perennials: once with a balanced slow-release fertilizer
- Roses: start fertilizing roses again if you stopped feeding over the summer, or to switch back to full-strength if you were feeding at reduced strength
- Cold-hardy shrubs: feed once with a balanced, slow-release fertilizer
- Other shrubs can be fed safely with an organic soil amendment this month
- Palms: feed once, and apply chelated iron if necessary
- This is the last time we feed palms until temperatures warm up again after winter
- Potted warm-season cacti and succulents: feed once this month
- Cold hardy trees that have been in the ground for longer than a year: feed with a balanced complete fertilizer
- Veggies and herbs: feed once with an organic fertilizer or an inorganic complete fertilizer
What to NOT Fertilize
- Anything that was just planted: wait until you see some new growth before fertilizing new plants
- Avoid fertilizing cold-sensitive plants this late in the year. A spur of new growth just before winter can leave cold-sensitive plants more vulnerable to frost damage
Prune, Divide, and Conquer
- Remove summer annuals to make room for cool-season color
- Remove spent flowering stalks from summer-flowering bulbs, but let leaves remain on the plant until they completely dry up and turn brown
- Cut back prickly pear or cholla plants that have been severely damaged by an insect infestation or disease to an unaffected portion of the plant. This will give them a chance to put on some healthy fall growth when these insect and diseases are less active.
- Bermuda lawns that won’t be overseeded can be mowed back to 1” this month, other lawn types can be mowed regularly as necessary
- If you’re overseeding, mow your bermuda lawn back to ½” inch before spreading seed
- Divide daylilies every 3-4 years in September if they’ve become too crowded and you live in a cooler part of the region. If you live in a warmer area don’t divide daylilies until temperatures have cooled down in October.
- Roses: prune lightly after temperatures have dropped below 100°F. Remove dead or diseased canes, remove canes coming up from below the graft, pluck off yellow or unhealthy leaves, and remove all of the fallen leaves from underneath the plant.
- Watch for any hollowed-out canes as you’re pruning. This is a sign of cane-boring insects. Cut the cane back until you see no more sign of the damage, and apply some white carpenter’s glue to any cuts that were made on living canes to keep borers from re-infesting the shrub.
- Summer-flowering, cold-hardy shrubs: prune back this month to reshape, thin, or control size. Summer-flowering shrubs that are frost-tender can be deadheaded, but don’t cut them back severely this month, save that for springtime after all chances of frost have passed.
- Prune desert legume trees lightly to remove unwanted suckers that have sprouted over the summer
- Divide chives, oregano, marjoram and mint if they’re become too overcrowded
- Prune scented geranium, rosemary, lavender, sage and thyme by up to 1/3 of the plant’s size if necessary this month to refresh the growth
- Don’t prune any frost sensitive plants this time of year. It’s best to not encourage any new growth on these plants until after winter has passed.
For the Fruits and Veggies
- Begin to cut back on fruit tree watering frequency until you’re watering every 2 weeks once temperatures drop below 100°F
- Fertilize grapes for the last time of the year this month
- Clean up any fruit that drops from your fruit trees to help keep pests at a minimum
- Water veggies daily, and give them at least one deep soak this month to move salts away from root zones
- Feed veggies and herbs once this month with either an organic fertilizer or an inorganic complete fertilizer
- Sow winter veggie seeds: snap beans, beets, bok choy, Brussels sprouts, cabbage, carrot, celery, collard greens, cucumber, endive, fennel, kohlrabi, leek, lettuce, mustard greens, peas, radish, spinach, Swiss chard, turnips
- Plant winter veggies: broccoli, Brussels sprouts, cauliflower, and potatoes. Plant garlic, and onions later in the month once temperatures have cooled.
- Plant Strawberries!
- After you see new growth on your newly planted strawberries, feed them with a balanced, water-soluble fertilizer mixed at a low concentration
For the Lawn
- Overseed Bermudagrass lawns late in the month to early October (cooler areas can overseed in September, warmer zones should wait until October)
- Slowly cut back on watering frequency and mow the lawn to ½ inch before overseeding to coax the Bermudagrass into dormancy a little earlier
- Don’t overseed a new lawn, wait until it has been growing for at least a year so that it is well established before introducing another type of grass to compete for space and nutrients
- Keep watering your lawn on the same schedule (every 4-7 days to a depth of 8-10 inches) until temperatures drop below 90°F
- Feed Bermuda lawn once this month with a balanced fertilizer that is high in potassium and phosphorus
- Unless you’re overseeding, this will be the last feeding your lawn will need until it shows new growth again next spring
- Feed zoysia or St. Augustine lawns once this month. This is the last month that they need to be fertilized this year
- Bermuda lawns that won’t be overseeded can be mowed back to 1” this month, other lawn types can be mowed regularly as necessary
- If you’re overseeding, mow your bermuda lawn back to ½” inch before spreading seed
Water Wisely
- Begin to cut back on watering frequency as temperatures continue to cool, especially with plants that are sensitive to the cold
- Check potted plants daily for watering needs. Watering is only necessary if the soil is dry one inch below the soil surface
- Water newly planted annuals daily to a depth of 6-8 inches until new leaves begin to emerge, then gradually cut back on watering frequency to every 3-4 days
- Cut back on watering any warm-season succulents that begin to go dormant this month
- Keep watering your lawn on the same schedule (every 4-7 days to a depth of 8-10 inches) until temperatures drop below 90°F
- Continue watering roses every 3-5 days to a depth of 2 feet
- Water established shrubs every 2 weeks to a depth of 2 feet
- Established trees: water once this month to a depth of 3 feet, less mature trees can be watered twice this month to the same depth.
- Water veggies daily, and give them at least one deep soak this month to move salts away from root zones
After temps drop below 100°F
- Larger cacti, agaves, and yuccas: cut back to watering every 5-6 weeks to a depth of 3 feet
- Smaller cacti, succulents, agaves, and yuccas: apply water every 3-4 weeks to a depth of 1-2 feet
- Begin to cut back on fruit tree watering frequency until you’re watering every 2 weeks
- Perennials: begin to increase the amount of time between water applications to every 5-7 days to maintain soil moisture 1 foot deep
- Perennial herbs: slowly stretch out the time between water applications to every 4-5 days to a depth of 1 foot (or deeper for larger plants)
General Chores
- Begin to prepare new beds for fall planting if you haven’t already
- Begin to pre-chill bulbs that require chilling to bloom (tulips, hyacinth) for 6-8 weeks
- Clean up any fruit that drops from your fruit trees to help keep pests at a minimum
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
