September is not the best time to put out bedding plants--many can be lost in heat waves and Santa Ana winds. But some gardeners are willing to take a gamble. Snapdragons and Iceland poppies planted now that survive will be in bloom before Christmas and will continue flowering until next summer. Sweet peas can also be planted now for early bloom.
To keep dahlias blooming into November, make sure they are well-watered and fertilized this month. Dahlia growers say that potash, in sulfate of potash, is beneficial for root growth and also strengthens the tuber for its winter dormancy.
Bulbs from warmer climates--South Africa, North Africa and the Mediterranean coast--can go in the ground right now: freesia, tritonia, ixia, watsonia and Dutch iris (originally from North Africa and Spain but hybridized in Holland). Other bulbs that can be planted now are Spanish bluebells ( Endymion ), ornithogalum, oxalis and ipheion.
Don't throw away eggshells; they are a wonderful soil conditioner and organic fertilizer. Instead, dry and crumble them, and work them into the soil of your vegetable garden.