For similar reasons to why it is a good time to plant plants in the fall, it can also be a good time to transplant them. (See the post from Sept 27th for why.) With transplanting, however, the plants aren’t neatly in pots, dying to be planted, they are already growing in your garden, so you have to give a little more thought as to whether it’s a good idea to disturb them or not.
A decent rule of thumb is to transplant/divide spring blooming plants in the fall, and fall blooming plants in the spring. When a plant is blooming, it has just expended a lot of its energy to make those flowers, and will expend even more in the near future to set seed, so it doesn’t have a lot of spare energy to rebuild itself in a new place. So if you really wish that your Asters were in a different place, make note of it, and do both of you a favor and move them in the spring. But if your Lady’s Mantle has outgrown its space, by all means, cut it up and move it around.
Dividing perennials is an involved subject in itself. Tools needed can range from a simple trowel to an axe or a saw (I’m not kidding!) And it’s always preferable to do a quick Google search on the particular plant that you are about to divide, in case it has any peculiarities. (Baptisia, and other plants with tap roots, for example, do not like being transplanted or divided much at all, so it’s best to know that going in.) But in general, when you divide something, you need to make sure that you have a decent amount of both root and shoot (stems) on each piece that you plan on putting back in the soil. That ensures that there are enough food gathering parts (the leaves) and water gathering parts (the roots) to help get the plant established.
As with any new introduction to the ground, an important thing is to water, water, water! As plants go into winter, they need a good store of moisture in their cells to help them survive. Transplanting and dividing on a rainy day is a great start.
So if you’re in a “tidying up” frame of mind, and want to move some things around, the next week or so is a great time to do it for certain plants. (It’s no coincidence that I send these blog entries out just before the weekend… 🙂 )