September Gardening
March is one of the most active months for gardeners in Southern Arizona, and many of the chores we busy ourselves with this time of year will set us up for success through the tougher weather to come. Insects are active, weeds are plentiful, and many of our favorite plants are ready to be pruned or planted! Stay ahead of the curve with this month’s gardening checklist.
What to plant in March:
- Plant warm season annuals
- Water every 3-4 days to a depth of 4-6 inches
- Variable weather conditions and increasing heat will affect how frequently water is needed – check soil before watering to make sure it’s necessary
- Sow warm season annual seed (cosmos, gaillardia, Mexican sunflower, sunflower, zinnia, hollyhock)
- Plant amaryllis, caladium, calla, crinum, manfreda, and spider lily near the end of the month (when soil temperatures are above 65°F, and air temperatures are steady above 70°F)
- Plant warm-season succulents now through May
- Protect from sunburn if necessary on the south- and west-facing sides of the plant
- Plant citrus trees
- Water 2-3 times a week for the first 4 weeks to get it established, slowly dropping down to every 5-7 days through the first summer. A normal citrus watering schedule can be established in fall.
- Wait a year before applying any fertilizer
- Sod or plant St. Augustine grass
- Water daily for 1 week, then every other day for the 2nd Begin to water more deeply to a depth of 4-6 inches on the 3rd week, and water just frequently enough to maintain moisture at that depth.
- Plant ornamental grasses now through May
- Plant spring- and summer-flowering perennials, and summer-flowering or cold-tender perennials once there’s no more danger of freezing temperatures
- Don’t fertilize newly planted shrubs or perennials until fall, and don’t prune unless it’s absolutely necessary for 1 year
- Plant containerized roses
- Plant desert legumes and desert-adapted trees, wait until after the last chance of frost to plant frost-sensitive trees
- Sow seed of black-eyed peas, cucumber, melons, okra, amaranth, basil
- Set out sweet potatoes, and Jerusalem artichokes
- Plant peppers and eggplant before mid-month
What NOT to plant in March:
- Bare root roses or deciduous trees – There shouldn’t be any left at retailers, but if you happen across any in a box store clearance sale, it’s best to avoid them this late in the year
- Wait until at least mid-month to plant frost-tender trees, shrubs, or perennials
What to fertilize:
- Fertilize newly planted annuals after 2 weeks, or when they start showing signs of new growth
- Fertilize every 2 weeks throughout the growing season with low nitrogen, high phosphorus formula
- Begin fertilizing growing and blooming containerized plants every 2 weeks
- Fertilize winter-dormant succulents only after a full set of leaves has emerged, but refrain from watering any winter-growing succulents
- Use a low-nitrogen water-soluble fertilizer for container plants mixed at half the strength recommended for houseplants
- Fertilize plants in the ground once this month as they begin to grow and once more about a month later
- Fertilize overseeded lawns with high-nitrogen or a complete balanced fertilizer, but refrain from fertilizing a bermuda lawn that isn’t overseeded.
- Augustine lawns can be fertilized with 5 lbs of a 21-7-14 blend per 1,000 square feet once they are actively growing.
- Begin to fertilize roses, following your preferred fertilizing schedule throughout the growing season
- Fertilize shrubs once in spring and again early in fall
- Fertilize summer-growing herbs with a low-nitrogen plant food
- Sidedress okra with a balanced slow-release fertilizer or apply a thick layer of compost
Prune, Divide, and Conquer:
- Remove winter-growing annuals as they begin to look tired and unhappy
- Thin annual seedlings regularly to make sure new plants have room to grow
- Cut back and/or divide canna this month if you haven’t already
- Resume regular watering and fertilize after cutting back
- If cannas were divided, resume regular watering and wait for signs of new growth before fertilizing
- Remove spent flowers from plants that grow from bulbs or rhizomes unless you’re saving the seed, but leave yellowing/dying leaves until they completely dry up on their own
- Remove frost damage from succulents with a sharp, clean cutting utensil for a smooth, clean cut
- Treat the cut with dusting sulphur to prevent fungal growth on the cut
- Cut back prickly pear and cholla if they’re overgrowing their spaces
- Treat cuts with dusting sulphur to prevent fungal growth on the cut
- Prune dead or damaged wood and crossing branches from citrus trees and remove low-growing suckers after the danger of frost has passed
- Thin and prune grape vines if necessary to keep them on their arbor or trellis
- Divide clump-forming perennials that have become too overgrown (every 3-4 years)
- Prune winter damage out of frost tender perennials, shrubs and trees after all chances of freezing temperatures have passed
- Water them well after pruning, and wait at least 2 weeks to apply any fertilizer
- Cut back basil regularly to keep it producing tasty leaves instead of flowers
- Remove side shoots from tomatoes to promote upward growth and fruit production
For the Fruit Trees:
- If you happen to have a fruiting olive, now is the time to begin treating with a product like olive stop or fruit stop to reduce pollen output and the production of messy fruit later on
- Water deciduous fruit trees weekly to a depth of 3 feet to keep them hydrated while they’re flowering and beginning to form fruit
- Start thinning fruit when they’re about the size of a walnut – this will keep limbs from breaking under the weight of too much heavy fruit, and will keep the tree from spreading its resources too thin, resulting in small fruit that isn’t as tasty as it should be
- Plums should be at least 2 inches from each other
- Apples, apricots, nectarines, and peaches should be at least 4 inches from each other
- Figs don’t have to be thinned, but they’ll grow a bit larger if they’re no closer than 3-4 inches from each other
- Pomegranates should be at least 6 inches from each other
- Prune dead or damaged wood and crossing branches from citrus trees and remove low-growing suckers after the danger of frost has passed
- Thin and prune grape vines if necessary to keep them on their arbor or trellis
- Watch grape leaves for signs of grape vine skeletonizers and hand pick them with a pair of gloves on, or treat with Bt (Bacillus thuringiensis) if necessary.
For the Lawn:
- Sod or plant St. Augustine grass
- Water daily for 1 week, then every other day for the 2nd week. Begin to water more deeply to a depth of 4-6 inches on the 3rd week, and decrease frequency to water just often enough to maintain soil moisture at that depth.
- Water Bermuda lawns every 2 weeks
- Overseeded lawns need deeper water this month – water to a depth of 8-10 inches and water just frequently enough to maintain moisture at that depth.
- Fertilize overseeded lawns with high-nitrogen or a complete balanced fertilizer, but refrain from fertilizing a bermuda lawn that isn’t overseeded.
- Augustine lawns can be fertilized with 5 lbs of a 21-7-14 blend per 1,000 square feet once they are actively growing.
Water Wisely:
- Continue watering cool-season annuals regularly if you’re planning to collect seed
- Water growing or blooming bulbs to a depth of 6 inches when the soil surface is dry
- Increase watering frequency on iris as the temperature rises, water iris once a week when the temperature is above 90°F
- Step up watering of warm season succulents to twice a month to a depth of 8 inches to 3 feet (depending on the size of the plant), while simultaneously slowing down the watering frequency of cool-season succulents by a few days
- Watch for the first leaves to show on winter-dormant succulents and begin watering regularly when they start showing signs of life
- Water deciduous fruit trees weekly to a depth of 3 feet to keep them hydrated while they’re flowering and beginning to form fruit
- Water Bermuda lawns every 2 weeks
- Overseeded lawns need deeper water this month – water to a depth of 8-10 inches and water just frequently enough to maintain moisture at that depth.
- Water perennials just frequently enough to maintain soil moisture at a depth of 2 feet
- Water roses around every 5-7 days to a depth of 2 feet
- Water non-native shrubs every 2 weeks to 2-3 feet, depending on size, established native shrubs don’t need water quite as often as non-natives
- If you have tree basins or berms around your trees for watering, check them now to make sure they still extend a foot or two beyond the tree’s dripline
- Step up watering frequency for trees as necessary to maintain soil moisture at a depth of 3 feet.
- Water veggies daily to 6-12 inches deep
- Water herbs every 3-5 days
General Chores:
- Get out and see the wildflowers!
- Weeds are heavy this year from the great winter rains we’ve had – remove as many as possible before they go to seed
- Watch for the beginnings of any insect infestation and treat plants early with a hard spray of water or a dab of insecticidal soap to avoid having to treat larger populations with chemicals later on
- Avoid spraying plants with systemic or broad-spectrum pesticides when they’re flowering or in bud – doing so may kill important pollinating insects
- Apply a 2-3 inch layer of compost or mulch to perennial beds and over the root zones of shrubs and trees
- Avoid piling mulch against trunks or woody stems
- Thin side buds that emerge around a hybrid tea rose flower, and thin the center bud out of clusters of floribunda, grandiflora, or shrub roses for larger blooms
- Mulch around the roots of roses if you haven’t already
- Watch for powdery mildew on your roses and treat early if you see white patches forming on leaves
- Harvest garlic when the top part of the plant is almost all dry. Save at least one head to replant in fall.
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
