Here's a lovely sight:
Yes, couch grass.
I have a new client, he has a couple of large beds which are fully, absolutely and totally infested with couch grass.
How depressing! Luckily he found me, and I am now digging my way to victory.
In cases as bad as this, there is only one thing to do: you have to clear out the entire bed, lifting all the plants, cleaning off the couch grass, digging out all the roots, then replanting.
Best practice is to get a couple of buckets of water, some stout plastic bags for the rubbish - old compost or bark chip bags are perfect - and a large plastic sheet.
Spread the plastic sheet out at the edge of the bed, and put the good plants on it as you go, to keep them all in one place, and to avoid getting muddy footprints all over the lawn. It also gives you a working area to clean out the roots and shake off the soil.
So, Dig Once:
Dig out the good plants: firstly loosen the soil all around them. Lever them up, shake off as much soil as you can, pulling out every couch grass root that you see. Put bulbs and clumps on the sheet, put soft-rooted ones in the buckets to keep them moist.
Dig over the ground, pulling out the couch grass as you go. Don't pull at it so much that it snaps - loosen an area, then get the fork underneath it, lift, and "bounce" the soil on the fork, to get as much off as possible. Ease out the long couch grass roots, trying not to break them. I usually work from one side to the other, in fairly narrow strips, so I can pull out a handful of long roots, leaving a lot of loose ends on the un-dug side: then I dig the next strip, getting out another handful of long roots, snapping as few as possible. Hard to describe, easier to demonstrate. Put all roots, weeds etc in the rubbish bags. Don't even think about composting them: they should go straight to the tip, the bonfire or the brown bin, depending on your area.
Once you've done the area, go back and dig it over again. You will pull out yet another bagfull of roots! This leaves the bed ready for replanting.
I rather think that if you dug for a fourth time, you would still be finding roots, but let's be honest, you have to stop somewhere, and by getting out the majority of it, any regrowth will be on very short lengths of root, and therefore easy to get out by normal weeding.
Having Dug Thrice, you can replant.
Having already taken care to shake as much soil as possible off their roots, and to pull out every scrap of couch grass you can find, this should be quite easy, but do look carefully at the roots of every single plant, before you replant it. With matted, clumpy perennials, you might need to soak the rootball in a bowl of water in order to pull the couch grass through and out without breaking it. If you don't do this, then by the end of the season you will be back where you started. In the very worst cases, you might have to discard some plants that are so badly infested that you can't clear it all out.
Having replanted, water thoroughly. Sit back and admire. Leap to your feet in horror at all the bare empty soil. Rush off to buy new plants. Fill in the gaps. Sit back and admire.
Here is the same bed at Dug Twice stage:
Not finished yet, quite a lot of bits still visible, so back I go and Dig Thrice, as above.
After cleaning off the plants, I put back the decent ones, and here is the result:
OK, the bulbs are looking very sad, they always do once they've been lifted. But I instructed the client not to trim back the leaves but to let them die down naturally.
I love it when the client comes out two hours later and says "My! I never knew I had all those Peonies!".
In this case, knowing that Peonies don't like to be disturbed, I managed to work around most of them by loosening the soil all around and - as everything was at that point bone dry - gently pulling out the lengths of couch grass through the Peony, without having to lift the entire plant. I'm cautiously optimistic that I got all of them: and if not, once they have flowered, then I will just have to go back and lift the entire plant in each case, clean it of all couch grass, and replant it.
In the case of the big one, it was so badly infested that there was no choice but to lift it, clean it, and replant it.
Most gardening books will tell you that Peonies will sulk for one/three/five/seven years after being lifted: this is simply not true. They will sulk and refuse to flower if you plant them too deeply - and as they are substantial plants, there is always the tendency to plant them deeply.
The trick is to remove about half of the leaves, to reduce the weight of the plant: dig a shallow bowl, make a heap of soil in the middle of it, spread out the fat tubers around the heap, then cover them over with soil and press down gently. If the plant still tends to fall over, either take off more of the foliage, or carefully push a stake or two between the tubers (you may have to uncover them, to avoid spearing them) and tie up the foliage. If there are stout flowering stems, then frankly you may just have to admit that it won't flower this year, and chop them off.
So there you go, how to remove Couch Grass. Easy! *wry smile*