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Posted: Sun Sep 02, 2007 12:18 pm
by gareth_glyn
We are being sent slowly mad by weeds in a pathway that we intended to be pretty low-maintenance.
It consists of slate chippings on top of a weed-proof membrane, but weeds of all sorts and sizes just love germinating in the slate waste itself. We've spent untold hours pulling them up, even using several kinds of weedkiller (including sodium chlorate) to control them, all to no avail. Quite often new ones appear overnight.
Nearby, a public footpath through the countryside is made in exactly the same way, and is more or less weed-free (except for the edges) all year round.
What are we doing, or have done, wrong? Is there a 'grade' of slate chippings that is not suitable for this use, for example? - because in another part of the grounds around the house we have much larger chippings on a membrane (not a path, so never walked on) where weeds have never appeared.
We're utterly flummoxed, and may in the end have to resort to tarmac, which we really, really, don't want to do.
Any help gratefully received.
Gareth
Posted: Sun Sep 02, 2007 3:31 pm
by seanandruby
Did you dig weeds out, also treat with weedkiller before you covered ground? i did mine 2 years ago, dug out, treated and covered with Terran and I'm still weed free. Terran is a lot thicker than the stuff you get from garden centres. also make sure you have ample cover of slate and treat with weedkiller from time to time. Hope this proves useful
Posted: Sun Sep 02, 2007 5:20 pm
by gareth_glyn
seanandruby wrote:Did you dig weeds out, also treat with weedkiller before you covered ground? i did mine 2 years ago, dug out, treated and covered with Terran and I'm still weed free. Terran is a lot thicker than the stuff you get from garden centres. also make sure you have ample cover of slate and treat with weedkiller from time to time. Hope this proves useful
Thanks, Sean - yes, we had it all done professionally with the right stuff membrane-wise, but our problem is that the weeds actually germinate and set root in the actual slate topping itself - they don't come through the membrane. It's as if the crushed slate is as attractive to them as topsoil would be.
What's even more inexplicable is that I've dosed the whole path on more than one occasion with sodium chlorate, which is supposed to not only stop and kill weeds but also to sterilise the ground for months. I might just as well have used water, for all the weedkilling the sodium chlorate did.
I'm glad to hear, though, that slate chippings can work (as in your case) - maybe, as I suspected, it's because the crushed slate we got was just too crushed, and functions like soil.
Posted: Sun Sep 02, 2007 6:07 pm
by scoffsred
I'm not sure the sodium chlorate will be sterilising the ground, i know in the case of glyphosate it is neutralised as soon as it touch's the ground and becomes a fertiliser, as for the slate, unless its almost powder form it shouldn't harbour weeds, it could be that it's too deep and is contamminated with soil of some kind.
Posted: Sun Sep 02, 2007 8:46 pm
by Dave_L
Can you not treat the chippings with a good dose of sodium chlorate?
Posted: Sun Sep 02, 2007 9:07 pm
by gareth_glyn
Dave_L wrote:Can you not treat the chippings with a good dose of sodium chlorate?
I've tried sodium chlorate on two occasions, without success (see upthread).
Posted: Sun Sep 02, 2007 9:30 pm
by Dave_L
Hmmmm that surprises me......whenever I've used it, nothing grows there for a good few months/years!
You gave it a real good dosing? 
Posted: Sun Sep 02, 2007 9:48 pm
by seanandruby
maybe the slate is soaking the weedkiller up straight away, so its not getting to the weeds. maybe try soaking with water first then weed killer. I would agree with scoff that it may be harbouring soil, also wind blown seeds and grass cuttings. pull some slate back and see if there is soil there. its like the in-laws ...as you get rid off one another turns up 
.
Posted: Sun Sep 02, 2007 9:59 pm
by Rich H
The key to any mulch over membrane is to have it as thin as possible. In the case of slate chippings, a max of 20mm, well washed.
Posted: Sun Sep 02, 2007 10:31 pm
by gareth_glyn
Rich H wrote:The key to any mulch over membrane is to have it as thin as possible. In the case of slate chippings, a max of 20mm, well washed.
It may be the 'well-washed' part that's important.
Thanks to all who've responded - it's all a great help, thank you.
Gareth
Posted: Mon Sep 03, 2007 10:24 am
by Rich H
Straight out of the bag there is always a sludge of wet fines. This sludge is perfect for weeds and should be rinsed off.
Posted: Mon Sep 03, 2007 11:10 am
by gareth_glyn
Rich H wrote:Straight out of the bag there is always a sludge of wet fines. This sludge is perfect for weeds and should be rinsed off.
Thanks, Rich - I think I may be homing in on the cause of my problem!
It looks as though we'll have to take up the whole lot and wash it, or start again with new stock.
Posted: Mon Sep 03, 2007 12:30 pm
by Tony McC
I'm stunned that Sodium Chlorate, which we refer to as "Death Juice", is not working. I'd be wondering about the strength and/or the viability (if that's the right word) of the stuff, because I've never known it not to work, even on slate chippings.
Some years ago I was involved in a large project that used thousands of tonnes of slate waste, with pieces ranging from definite "lumps" right down to dust, and once doused with Death Juice, nothing, not even dandelions, would germinate on the exposed surface. While washing-off can;t do any harm, I reckon a fresh batch of Death Juice is the likely answer.
Posted: Mon Sep 03, 2007 12:42 pm
by gareth_glyn
Tony McC wrote:I'm stunned that Sodium Chlorate, which we refer to as "Death Juice", is not working. I'd be wondering about the strength and/or the viability (if that's the right word) of the stuff, because I've never known it not to work, even on slate chippings.
Some years ago I was involved in a large project that used thousands of tonnes of slate waste, with pieces ranging from definite "lumps" right down to dust, and once doused with Death Juice, nothing, not even dandelions, would germinate on the exposed surface. While washing-off can;t do any harm, I reckon a fresh batch of Death Juice is the likely answer.
I'll certainly give it a whirl.
The first two lots I bought were in crystal form and needed to be dissolved - this was quite difficult until I found that giving it time, rather than the vigour of the stirring, was the best way to ensure it dissolved completely.
When these didn't work, I bought a ready-mixed liquid version just in case I'd got my quantities wrong or something; this certainly killed the weeds that were there, but didn't prevent new ones from sprouting almost immediately.
I'd be very open to suggestions as to the strength of the solution of 'death juice', best way to distribute it etc.
Meanwhile, I've just completed about 12 hours (in 3-hour batches) of back-breaking work clearing the path of weeds - this will be the ideal time to give the sodium chlorate another try.
The path, by the way, is about 90 metres (almost 300 ft.) long.
Posted: Tue Sep 04, 2007 11:57 am
by Tony McC
We normally use the crystal form and follow the instructions on the pail - not sure what the dilution is off the top of me head.
Normally we'd apply via a red watering can (the colour of the can doesn't really matter, but by using the red can, there's no chance of it being used a couple of hours later to water me fuchsias) and make sure the ground/sub-base is soaked, with every square millimetre covered.