I'm planning to plant some blueberries and would like to mulch with something that would really prevent weeds for many months.

I've tried previously hay, for other plants, but even 2 inches applications end up flattening and compacting itself after a few rains, then weeds creep up.

After doing a lot of searching, I've stumbled across perlite : it cannot degrade or flatten itself, allows exchange of water and air, and doesn't heat up in the sun like rocks do.

Besides the high cost, what would be the other pitfalls, if any ?

Perlite floats. When you water, or when it rains, it will wash away.

Over time, Perlite absorbs minerals and can become toxic. Soil makers stopped using it, and to a lesser extent, Vemiculite, for that reason.
A great mulch that blocks weeds is newspaper, and paper bags. weigh them down with pine bark nuggets. Use pine bark nuggets instead of mulch because the mulch contains a ton of weed seeds. Nuggets are very clean---especially if you only use the larger chunks. Pine bark is also acidic. The blueberry bushes like that. Test your soil before you plant the bushes. If the pH is higher than 6.8, you will have to add sulfer to the soil to lower the pH. A great annual fertilizer for blueberry bushes is Espoma's Holly Tone. Not only is it a great fertilizer; it keeps the pH level down to the plant's liking. Good luck! There's nothing like fresh Bberries on your morning cereal!

MsDoe said:Perlite floats. When you water, or when it rains, it will wash away.

Yes,
it has the same pitfall as other light mulching materials.

To resolve this problem, i was planning to use a fine aluminum mesh like this one: https://apfuhuawire.en.made-in...
over a rigid frame ( 2 feet by 2 feet, 1 or 2 inch thick) to enclose the perlite (using the biggest size of perlite available).

Then i would just lay it on the ground without fear of the perlite washing away.

Again, that's involved and costly, but it would probably last dozens of years and would be scalable in size.

Sscape said:Over time, Perlite absorbs minerals and can become toxic. Soil makers stopped using it, and to a lesser extent, Vemiculite, for that reason.

Damn.

I already had bad experiences with vermiculite in my potting mixes, as it created weird nutrient deficiencies.

I was hoping perlite would be different.

Can you please point me to the published facts ?

Sscape said:A great annual fertilizer for blueberry bushes is Espoma's Holly Tone. Not only is it a great fertilizer; it keeps the pH level down to the plant's liking.

Thanks for the tip !

I will check it up.

You do not want to use perlite. If it retains water like you hope, it will start to harbor dirt and algae.
I would use chocolate brown mulch. I use it in most of my beds and at 2" deep, 95% of the weeds are discouraged. The few that aren't, pull right out easily.

Lay either newspaper, papperbags( my favorite), or cardboard down.
Cover with hardwood mulch.

What about expanded clay granules ?

Any pitfalls, besides price ?

They float worse then perlite.

I would also like to see some published facts regarding perlite becoming toxic by absorbing minerals. 'Perlite' is really expanded perlite. (Perlite is a rock.) Unlike vermiculite (expanded mica), the air "compartments" are closed, and cannot be compromised. It is only the rough surface of the expanded perlite granules that can hold water or other particles. This why expanded perlite floats so well, and will never every become waterlogged.

How many bushes ?

I use rubber tree rings around my freshly planted bushes and trees
these rings have lasted years and been used for several plants




they cost me less than 10 a piece and come in different sizes and colors

Fred,
I don't know what kind of area you're in out there in Montana but out here in the East (where everything is acidic). Pine needles make a great mulch for this purpose. They take quite a while to break down, are comfortable under foot, allow water and air filtration, suppress weeds, and are free. I have a gardening friend who laughs herself silly because she bags up tons of pine needles and drives them over to me. I use them in my perennial beds, around my raspberries/blueberries and garden walkways. It's a win-win.

Two inches of hay (or straw) isn't near enough to do the job of weed suppression. I used to have a large vegetable garden - 60x90ft. When the ground warmed and everything was planted, I put down hay (not straw), but did not break apart the bails into fluff. This is a big mistake, in my opinion. I divided the bails into 3-6 inch slabs. (The bails naturally come apart that way.) So the slabs are shaped like thick 18 in. square paving stones. These are laid out between the rows like a checkerboard. I never needed to weed and almost never water, for the rest of the year.

But straw or hay (especially hay!) will introduce a lot of weed seeds. It was never a problem for me except for weeding that needed to be done before the slabs were laid.


Edited for grammaer

gardengus said:How many bushes ?

I use rubber tree rings around my freshly planted bushes and trees
these rings have lasted years and been used for several plants




they cost me less than 10 a piece and come in different sizes and colors

They're known to leech heavy metals.

I use pine needles (in Maryland) and they work well.
The perlite and screen just seems like overkill. Like when people use landscape fabric but find out things don't work as desired, then the fabric is a nightmare, a lot of work to remove. Perlite is also bright white. I think it'll leak out from the frame.

Maybe I am not being open minded.
also I am not sure 2 inches of perlite will really block seed germination. Put 2 inches in a large clear plastic container and shine a flashlight underneath, can you see the light?
And creeping weeds with rhizomes, like some grass. will go right under and come up. Then you're in the 'landscape fabric problems' boat.

I used straw in the vegetable garden with good results this summer, was much better at weed blocking than I expected.

I go for natural mulch which becomes a soil amendment over time, such as pine needles or straw. Blueberries have fine shallow roots that would really like the pine needles or another organic surface mulch.

Remember your local university extension service for good advice
https://www.montana.edu/smallf...

Even the coarsest expanded perlite will have fines, and the more you work with it, the more it brakes apart. If you pour some coarse expanded perlite into a bucket, for instance, you will produce a cloud of white dust. You don't want to do this inside the house! Yes of course, you will always have the white stuff escaping and causing an even more untidy look. This in addition to the possible task of keeping it clean. From day one, you will have junk blowing in, leaves falling, seed dropping, etc., that immediately make the perlite look dirty. You cannot remedy this. Whether this is a problem for you, maybe not, but it will always look crappy.

We (perhaps mostly me) have been focusing on all the pitfalls of perlite used this way, but would it actually work to suppress weeds? I think Sally is right: I don't think so.

Do not use pine bark nuggets, they also float away in a rain. Pine needles are the better mulch for blueberries, and they're free.
You will have weeds coming up through ANY mulch if they weren't removed from the planting ground in the first place, and it is nearly impossible to get all of them. But using a fairly thick mulch makes them weaker and easier to pull.
I'm not a fan of any kind of clever before the mulch other than plain cardboard, which is organic and breaks down over time.

with everyone who has suggested pine needles. They make a wonderful, fragrant mulch, acidify the soil, and break down slowly. As also mentioned above, organic mulches also improve your soil.

@frederick11 It seems like you're trying to re-invent the wheel with ideas about perlite, clay balls, etc. Nothing, repeat nothing, will totally eliminate weeds. Even if you pour concrete, they'll sprout in the cracks. You can control their spread by preventing them from going to seed and by pulling a few regularly as they come up, but they are always going to around to some degree.

@Sscape, I can't find any sources that back up your statements about perlite and vermiculite except for one study about sterilizing perlite for re-use in tomato crops which is not applicable to what you're contending. Provide us with cites?

If pine needles "break down slowly", how can they effectively acidify the soil?
I agree that they look pretty but there are better ways.

Point taken. But eventually more acid than perlite