September is the month for continuing to harvest and preparing for winter. As the weather can turn at any time it is best not to leave things for the last minute. So preparation for winter is vital.
If you have any winter crops or early crops they need to be planted.
Often September is a warm month however watering should not be as vital now, just keep an eye on things.
Things are winding down now which gives you more time to keep on top of things on your plot.
Although weed growth is slowing down, keep on top of them.
Make sure you have cleared out any areas that have finished cropping and composted (where appropriate) the remains. Then dig over the soil.
Make sure you have protection in place or available for all your winter crops. Protect your bare ground with green manure.