Thanks for your question on preventing weeds from growing between concrete slabs. I'm sure @EricL will be able to assist you with this question when he's back on the site later today. Also tagging @Adam_W in case he has any suggestions.
In the meantime, have a look at our Best Advice article on How to control weeds in the garden. You may also want to check out this recent discussion on How to repair and renew concrete driveway? It also includes some pointers on removing weeds.
Hope this helps.
I have some bad news for you. I don't think that anybody can guarantee you that you will be able to stop weeds growing in cracks in concreate/paving. The gaps will have soil/sand in them which will host weed seeds. If you pull the weeds out - it makes room for new ones to grow You can minmise it by sweeping concrete/sand mix into the cracks instead of just plain sand. in my paving at home (which I did myself so there are a lot of cracks) I use a once-a-year path weeder. Doesn't solve it but it helps a lot.
This is the one that I use, but there are a range of others wherever you buy your herbicides. Yates 1L Path Weeder Concentrate - Bunnings Australia
I'm afraid weeds are very tenacious and very difficult to get rid of. They grow almost anywhere and on anything if given the right set of circumstances. I agree with @robchin's recommendation of putting in a bit of concrete/sand mix to control the weeds. Even this mixture is not able to stop them totally, should they find a gap in the mix they will come out and grow again. Using herbicides should also help control the weeds in your path and garden. I propose a quarterly clean-out of the gaps so that you don't have a large weed infestation at the end of the year.
If you need further assistance, please let us know.
Thats is a nice strip of grass you have there
If you cleaned out the grass and used a grey colored sikaflex Pro + Plus a industry standard polyurethane sealant that would totally block the weeds as sika flex is strong and weeds shouldnt survive with out water light and air. Designed for expansion joints and weather.
Why wouldnt a flat slab be any less worthy of sealing properly
Sika 310ml Grey Concrete Sikaflex Pro+ Polyurethane Sealant I/N: 0083588 $21.79
I have another way of thinking about this.
Go with the flow and plant violet seed or a hardy low herb in the cracks and let them live forcing weeds out when established,
We have a native violet in our garden and it looks ok so I just let it grow in our cracks as it isnt invasive enough to damage concrete so its a boon not a bust.
We are mentally ok with this idea change and there you have it no more problem,
I must congratulate you on growing better looking grass(?) between concrete slabs than I can on my lawn. 😔
Personally, I love the smell of burning weeds in the morning. Try a butane weed killer - but ya gotta get'em before they reach the stage seen in your photo above.
And you don't have to incinerate (but you can - and it's fun!) the weed to kill it. Doesn't take much heat - they die quickly - as a weed should.
I normally spray my gas torch a real bugger to light,
Do you think this kills roots too? Thanks.
Afternoon JR @Jewelleryrescue
"Do you think this kills roots too?"
I believe so, or certainly it was mentioned, on the packaging blurb.
But let's conduct an experiment to see.
I'll check this area on a regular basis - where those two weeds once lived - and see if they dare return.
Thanks most kindly doing experiment it is intersting.
When I get the chance I am going to clean out a cement crack and using sikaflex pro+ polymer joint sealler in the crack and see if any weeds break through that.
No light no air no water no where for seed to take it might be a winner too.
it would be like a black plastic sheet over them.
Ok adding sika pro + to shopping list.