September is one of the busiest garden months and heralds the switch from summer-blooming flowers to winter and spring ones and from warm-season to cool-season vegetables.
As the weather can still be very hot, start slowly by cutting down faded flowers and vegetables and preparing the ground for the best planting month of the year, October. Continue to water deeply, early in the day or in the evening. Check drought-resistant plants for signs of stress. One deep watering now can tide them, trees and shrubs over until the winter rains and help protect them from disease attack.
Mid-month is the time to start buying spring bulbs. Choose the largest, fattest bulbs which create the biggest blooms, and leave intact daffodils with three or more divisions.
Bulbs to plant in September include the daffodil types that naturalise readily, known as Tazetta types, including the paper whites. Dought-resistant bulbs which require little or no watering in summer should be planted now.
Lilies need excellent soil, good drainage, lots of moisture, a cool root run, sun for the flowers, and little wind. Overall, new varieties thrive better here than older ones. Trial and error is the best guide to what will do well in your garden. Plant lilies as soon as you get them as the must not be allowed to dry out and work bone meal in below the roots. Usually they should be planted at twice the depth of the bulb. Begin feeding when the first sprouts appear.
Daffodils, grape hyacinths, hyacinths, ranunculus and tulips should not be planted too early, so store in a cool dry place. For best results, chill hyacinths and tulips in October for six to eight weeks in the refrigerator drawer before planting, but do not allow to freeze or store in plastic bags.
Irises need to be divided every three or four years or they will cease blooming. You can divide them between mid-September and mid-October. Otherwise, remove damaged leaves, tidy the ground and mulch.
Purchase cyclamen now, either as plants or tubers, for planting out in pots or in the ground. Look for tubers which are already beginning to sprout and plant so the tuber’s top half is above the soil’s surface. Use moist, humus-rich soil and keep damp until well rooted. Place in a semi-shaded spot. Once well rooted and the leaves have begun to grow, start feeding regularly, but do not over water.
Tropical's and sub-tropical's
This is their last growing month, so it is the last time to give only a fast acting fertiliser, if necessary, as they should slow down in October and harden off for winter during November.
In coastal areas, it is the last month to plant tropical's such as bougainvilleas, hibiscus, lantana, and tropical flowering trees. Inland, it is best to wait till spring because autumn planting leaves them vulnerable to possible frost. Don’t let newly planted tropicals dry out in September heat – hose the surrounding area twice a day to raise humidity during hot spells.
Hibiscus should not be pruned this month, but bougainvilleas, plumbago and oleanders can be pruned now after bloom. For oleanders, every year cut several whole stalks which have bloomed back to the ground but don’t cut off tops like a hedge as this does not create fresh growth from the ground.
Citrus and avocados
Keep citrus trees evenly watered. Roots that go dry can result in split fruit. Fluctuations in fertiliser levels can also lead to split fruit. Thick-skin varieties are less vulnerable.
If lemon trees have some brown fruit and some ripe, the brown fruit are probably overripe, but should be removed. Brown blotches on most fruit, particularly those closest to the ground, may indicate brown rot, caused by fungi living in the soil. If so, pick all the fruit, clean the ground below the tree and clip off any branches touching the ground as well as any dead or diseased growth. Water well then spray a fungicide in the early morning or evening over the ground and up into the branches, focusing on the lowest metre of growth.
Continue to water with three centimetres of water, but cut back to twice a week. Fertilise once a month. Plant out container roses.
Annuals and perennials
September is the first month to plant cool-season plants and the earlier into the ground, the more likely a bloom before Christmas. Much depends on the weather, but if they bloom in December they’ll keep on winter and spring, but it may not be until February or March.
Plant seeds of annual African daisy, calendula, cineraria, snapdragon and sweet peas. It is also a great time to plant perennials; some will go dormant and die back to their roots while they establish themselves, but should be back in spring. Tidy up existing perennials by cleaning the ground, check for snails, renew mulch and fertilise.
To keep the summer beds going a bit longer, remove faded blossoms, and fertilise with high bloom ingredients. If the bed is really tired, remove annuals and dig the beds, add soil amendments and replant in September with winter and spring flowers. For large tubs, replace about one-third of the soil with fresh; for smaller pots or those that are full of roots, provide completely fresh soil.
Maintain regular feeding of warm-season lawns, such as Bermuda and zoysia, but don’t fertilise cool-season grass until October. Water deeply but infrequently for warm-season grass and less deeply for cool-season.
Most summer vegetables will by dying back, so clear out what you can, and add manure, compost and fertiliser to the beds. To control pests, it is best to clear out all the vegetables at once and wait a week or two before new planting. If there is a serious infestation, such as caterpillars or whitefly, harvest everything, then spray the empty plants to kill off pests. Wait for several days before carefully pulling up the plants.
Vegetables to try now are broccoli, Brussels sprouts, cauliflower, leeks, lettuce, onions to produce spring onions, peas, potatoes, spinach and turnips. Broccoli, Brussels, and cauliflower do best from transplants, while onions are best from sets – November is when to plant sets of onions for slicing. Wait for the end of September to put in transplants of cauliflower and until October to put in cabbage and artichoke transplants.
If you attempt to plant seeds directly into the ground, a drip system will greatly increase success.