In article , Jake
writes
Glyphosate will only kill existing weeds.

There are a fair few already. Can't dig them out cracks are too narrow.


It will not prevent growth
of new weeds. Something like Pathclear will kill the existing stuff
(also slowly) but also has a residual action that will help to prevent
new weeds for about 3 months.

The slow-acting weedkillers are slow because they work down and kill
the roots. If top growth is killed too quickly, the roots won't be
killed properly and will regrow.

What a lot of people forget, though, is if using anything residual
like Pathclear you need to wet the ground as well as the plants! If
the cracks are very narrow, it may not be possible to get anything
into the cracks effectively.


That's what I thought except that i assume if one drenched the concrete
it would pour down the crack eventually?



With either type of herbicide, they will probably need a repeat
treatment to successfully kill off elder and dandelions.

That's what I thought!

--
Janet Tweedy