Gardening Problem: Overcrowded Plants

Years ago, a more experienced gardener told me: One way to keep weeds from getting into a garden is to plant things close together - so there's no room for weeds to get in.

I took that to heart when creating my flower beds... But perennials grow, and over the years can become crowded. Then they may disappear under the growth of other plants - like this sedum called "autumn joy." It's red flowers are barely visible.

There is no perfect time (in my opinion) to move plants when they become overcrowded. I often divide and move them in fall. The problem with that is that some of the early flowers are no longer visible. Some die down over the course of the summer.

I'm not sure how these two plants - yellow coreopsis and autumn joy sedum became so closely entwined. I'm going to try to separate them - but I don't want to disturb them while they're flowering. 

I'd also like to move a few more coreopsis plants closer to the pine trees. A lot of flowers don't do well in the acidic soil created by fallen pine needles, but the coreopsis seems to be fine.

Another way to keep seeds of weeds from encroaching on flowers is to add a thick layer of mulch. But squirrels have a nasty way of digging into the mulch and planting seeds.

In my yard, gardening is a constant battle between me and the squirrels!