So far, using a combination of weedkiller and excavation, I felt I was getting the upper hand over our Japanese Knotweed and wannabe Audrey III.
But this was no time to ease up. As they say, The best defense is a good offense, and I intended to be as offensive as possible. AS USUAL, right?
When last I left you, I was digging and burning and hating. It wasn’t enough! Here are the last steps in my technique.
- Drill. You are not going to get all the knotweed’s roots. I followed one down to a meter below grade, and then it took a turn straight down into the bowels of the earth. Spray the cut ends with…you guessed it! Let dry for a few days, and then take your drill and riddle the stinkers with holes. Cover each one completely with stump removing powder.
- Fill. Fill in with uncontaminated dirt back up to grade, compacting as you go. Get bog standard dirt – anything with lots of organic matter or fertilizers will encourage fleeceflower to come back, and it needs no encouragement.
- Cover. Get a big, nasty, impermeable tarp and cover the area. Go at least five feet beyond the kill zone. Weigh it down with big old rocks, and then cover the whole thing with landscape rocks or mulch. You won’t be growing anything here for a couple of years. I kept container plants on top.
- Patrol. By now, you know the shoots and leaves and even the roots of your enemy. Check beyond the edges of the tarp for signs of life. If the tarp heaves up somewhere from new sprouts, peel it back, spray, and re-cover. Repeat at least once in a couple of weeks, then cut it back, and re-tarp. Stay alert!
- Wait. And patrol. For a couple of years. You want at least a year to pass between the last sprout and the next step. Keep in mind it can re-sprout from rhizomes over ten years later. I had a resprout over a year after reading it the last rites, but I was able to bring the smackdown right away.
- Resume your life (sort of). Get some of the fancy-pants landscape fabric – the stuff that lasts 25 years with the rubberized backing – and replace the tarp. Cut holes to plant stuff through. Don’t spend a lot of money on plants for this area, ‘cuz you may have to move them. Keep an eye out for scary leaves. Gardening will never be the same (sob!), but your alert level can step down a bit.
I am aware that some of these steps may be superfluous or not supported by research (particularly the bits about hating), but hey: success. Also, I’m not really much of one for weedkillers usually, but this is an unusual case. Outside of the technique described here, controlled chemicals and injection equipment may give you good control. I did not cover those because they require licensure or a chunk of change to implement. My method: Cheap and Cathartic.
If you face knotweed, good luck, soldier!