We are just a few weeks away from losing the annuals to the first frost which is always sad. The cool nights have definitely started to take their tool on the flowers, and they are blooming less and starting to fight mildew. You should still feed the annuals because gardens usually give one last bang in October though.
Gardens still have plenty of weeding and cleaning, but you can start to cut things back before the fall rush and all of the raking starts. In some yards you can remove loads of greenery to see the better fall flowers. The fall is a great time to start your larger pruning too.
It will be time to turn off irrigation systems towards the end of October, before the first hard frost, and drain them out for the winter. After that you will have to water by hand.
October is also bulb month! Planting bulbs can be a lot of work, just when you thought your digging was over for the year, but you will be glad in the spring. Iris are particularly beautiful, drought tolerant, and will live forever if you divide them every few years (they make great gifts for your friends). Daffodils are know for repelling gophers, a big Santa Fe problem. Plant them is circles around the trees you are trying to protect. They too last many years. Other sturdy bulb flowers are crocus and mini iris, you can even plant them in cracks in rocks. Tulips do all right but expect them to get weaker every year. Species tulips, minis, are also hardy and will multiply and naturalize. If you have a clump of iris or daylillies that do not bloom much anymore, dig them up, separate them, and re plant them to revive the flowers for next year. Other perennials can be divided in the fall as well.