I sometimes find that some gardeners, especially newer gardeners, are a wee bit skittish about cutting back plants, lest they kill them.
In some cases, you do want to get rid of the plant, as in the case of these perennial sweet peas, Lathyrus latifolius, which I cut back to the ground on September 11th, less then two weeks ago. Look now at all that lovely new growth!
See, don't be afraid to cut plants back. Of course, do a little research to be sure it is a plant that can be cut back, and then if it is, do so. Do so like you mean it. No little trimmings and a nip here or there with your pruners. Be deliberate, be brave, be liberal in your cutting back. Many plants will come back after pruning with more vigor than you can imagine.
So, I guess I should not have been surprised to see these perennial sweet peas sprout back like this. Clearly, these sweet peas have not gotten the message that I am so sorry but they can't stay where I had them, they must go. The message they seem to have gotten from my cutting them back was "let's come back and make a go of it, strong than ever". It's a matter of survival for them. By pruning them back, I triggered all kinds of physiological changes in the plant, releases of different plant hormones, etc. that caused this to happen.
So I will need to resort to other means to get rid of these sweet peas. I can try to dig them out, but instead I will probably spray them with Perfectly Natural Weed and Grass Killer. Hopefully that will do the job on these perennial sweet peas.
Oh, I hate to think I am deliberately killing something called 'sweet', but dog gone it, it's not so sweet when it is all over the other plants in that particular spot. I promise, if the rain ever stops so the ground can dry out a little, and I can dig my new border, I will find a place for perennial sweet peas, because they are a wonderful addition to a garden. I promise!
Two answers to questions that might be asked:
I purchased the Perfectly Natural Weed and Grass Killer at WalMart. When I saw how well it worked, I went back and stocked up, because I knew by mid-July they would start stocking their "seasonal area" with Christmas merchandise, and stop carrying this. I refuse to call the "seasonal area" a "garden center" and I'm not going to admit that I look through there on occasion.
There are many good books on perennials and how to cut them back and manage them. One of the best I've found is The Well-Tended Perennial Garden: Planting and Pruning Techniques by Tracy DiSabato-Aust. I have an earlier edition and refer to it often. This newer edition would make a wonderful Christmas present for moi!