Preen isn't a weed killer per se -- it's a pre-emergent which means it prevents weed seeds from germinating. It won't do anything for the weeds that are currently in your beds. I have on and off used Preen in my gardens. I give all the beds a thorough weeding, apply the preen and then cover the beds with about a 2-3" layer of mulch. Honestly, I haven't noticed a huge difference between the years when I used it and the years when I didn't. I think it's more the mulch that's keeping the weeds down, but I'm sure the Preen doesn't hurt. If you do decide to use the Preen, you'll want to make sure you're done with any digging and transplanting. The Preen acts as a barrier and its effectiveness is reduced if you start disturbing the soil. Hope that helps some. Good luck.

Yes, as Dorothy said, Preen is not a weed-killer, it's a pre-emergent and its effect lasts for about 3 months, not more.
Whatever weeds are already in a soil they will grow thru it, but it will prevent FRESH seeds from germinating.
Application of Preen in April OVER the mulch reduced my maple seedling sprouting rate by 90% at least. In my garden any bare or freshly disturbed patch of soil has to be mandatory treated by Preen. And it works.

What George said...dead on. I wouldn't be gardening anymore without it...my back couldn't take it. MILLIONS of Norway seedlings spring up here every year. I do what George does; put it right on top of the mulch under our monster Maple and water in. I reapply usually in late June, first one is done in late March. They also make a Preen with fertilizer which I use in my beds. My beds are normally without mulch because I transplant so much it kinda gets "lost"....if you know what I mean. :) This year it will be going down soon.

Hey this is great. So it looks like consensus seems to be go with the Preen, and you've kindly suggested how i do it. OK. will do. In visiting the website it appears that organic Preen is the one to use with pachysandra, hydrangea etc v. the regular one. So i guess i'll do that. Thx Chitra

Just remember that it lasts a max of 3 months - which could mean a big flush of weeds in August. Been there, done that and what a mess!

A chemical-free option is to lay newspaper (about 8 sheets) down in your beds, in between and around the plants, and then to mulch on top of that.

Personally, I would weed the bed first, and then lay the paper and mulch, but I suppose you could try laying the paper right over the weeds and then mulching. The newspaper will smother the weeds and help prevent new ones from popping up.

:)
Dee

P.S. Have never tried it, but I've read that corn gluten works the same way as Preen, and is more environmentally friendly. I believe you'd have to use it in the same way as Preen (pre-emergent, etc.)

I think organic Preen probably IS corn gluten. I bet it's cheaper without the Preen canister.

Hmm, I never knew there was an organic Preen, lol. You're probably right - cheaper without the label, lol!

:)
Dee

I just looked at a friend's container of Preen the other day and IT IS corn gluten. I attempted to explain to my friend to just get the corn gluten, but sometimes people won't believe you if it doesn't cost them anything (my advice, I mean). Now I am looking for a source of corn gluten, I assume corn meal would work as well and I think I have read it will also suppress some diseases as well.

I am by all means not trying to squelch your attempts to organically control your weeds but I thought I should mention one potential problem with the product is that
it may attract rodents. Since it is a protein by-product, mice, rabbits and other rodents may be attracted to it. Frankly corn and its by products are the favorite food of rodents or so I have been told by the experts.
tomakers I would think that corn meal would be more expensive than corn gluten as there is no secondary market to sell gluten but there is nothing like a warm piece of corn bread. But I am interested to hear what you find.

Well, the cynic in me says that even if one is trying to stay organic (and I do garden completely organically) that buying corn gluten is probably a joke because it's most likely made with genetically modified corn. Sigh.

Anyway, this isn't a discussion of organic vs. non-organic, and I apologize if I seemed to try to make it one. I just like to gently suggest other options, and since the OP did ask for some, I offered.

Which brings me back to the newspaper. I am this very day going out to re-mulch a shrub border that I originally did last fall. Why re-mulch? Because when I filled this raised-bed border with trucked-in soil, and then mulched, I did not put down newspaper, (gosh, that soil looked so nice and pristine, lol!) and now it is absolutely covered in weeds, right through the mulch.

Soooo, off to weed, pull back the existing mulch, lay down a nice thick layer of newspaper, and re-mulch. That should keep it nice for a few years until the paper breaks down and it needs to be redone.

:)
Dee