September can be unpredictable in the north. Sometimes the weather is sunny and mild while other times the heat of the summer drags on or there's excessive rainfall. That unpredictability can be even worse in the South. You might still be plagued with excessive heat or in the path of a hurricane.
Find out what you should be doing in the garden in September, depending on where you live.
- Turn over your compost pile one last time.
- Clean up your flower beds. Cut back perennials that are done blooming. And trim off any dead or diseased vegetation. (Do not compost anything with disease.)
- Take cuttings from plants you want to propagate.
- Spray Japanese knotweed, a common garden weed, while it is blooming. The herbicide will have the most impact now.
Hot weather will likely continue in September in the Mid-Atlantic, but there will be mild days, too.
- Stop pruning and fertilizing, as you don't want to encourage new, tender growth just before cold weather arrives. But do continue watering plants, such as fall vegetables, that are still actively growing.
- Start bringing in houseplants that you have kept outdoors during the summer. But first, inspect them for insects and other pests that you don't want to bring inside.
Although the Midwest still sees some hot weather in September, the trend is clearly to more moderate temperatures.
- Plant a cover crop, which will help to avert soil erosion during the winter.
- In far northern regions, such as northern Michigan and Minnesota, plant spring bulbs.
- Plant fall-flowering annuals, which you can find at nurseries at a deep discount at this time of year. They will only last until the first frost, but they provide great color for the fall garden.
- Stop watering both evergreen and deciduous trees in late September. This will help them prepare for winter. Resume watering later in the fall after the deciduous trees have dropped their leaves.
- Divide perennials as needed.
- Dig and store tender bulbs, such as dahlias, cannas, and elephant ears.
September weather can vary in the Northeast, but overall it tends to be mild.
- Plant a cover crop to avoid winter soil erosion.
- In far northern regions, such as northern Maine, plant spring bulbs.
- Stop watering evergreen and deciduous trees in late September, but resume watering after the trees have dropped their leaves.
- Divide perennials as needed.
- Dig and store tender bulbs.
- Plant fall-flowering annuals.
- Harvest fall fruits and vegetables prior to the first predicted frost (which usually happens this month or the next). It's also a good idea to harvest ornamental gourds and pumpkins before a frost because they can suffer some discoloration from frost. A light frost won't hurt winter squash fruits, but it will kill the leaves; once the leaves die it's time to harvest because growth will stop.
The Pacific Northwest usually offers moderate temperatures in September with some rainfall.
- Plant shrubs and trees.
- Order spring bulbs.
- Weed your garden beds to prepare them for winter.
September weather in Northern California is moderate while Southern California weather is still warm with very little rainfall.
In Northern California:
- Keep harvesting summer fruits and vegetables.
- Start your fall/winter garden. Direct sow the seeds for beets, carrots, and radishes.
- Water fruit trees deeply, and clean up any fallen fruit as part of your pest/disease control efforts.
In Southern California:
- It is time for the fall vegetable garden. Start seeds of heat lovers, such as tomatoes and peppers.
- Direct sow the seeds for lettuce, collard greens, onions, peas, beans, and broccoli.
- Sow the seeds for cool-season annuals.
- Harvest fruits and vegetables as they ripen.
In the desert, temperatures start to moderate in September. But some areas might still see triple-digit temperatures with hardly any rain.
- Pick fruits and vegetables as they ripen.
- Plant new cacti.
- Practice whitefly control on plants, such as lantana. If you spot any whiteflies on the undersides of the leaves, immediately spray with neem oil.
The weather can start to become a bit more moderate in September in parts of the Southeast with some rainy days.
- Start your fall vegetable garden.
- Plant cool-season annuals.
- Pick ripe fruits and vegetables.