After redoing a garden bed in preparation for planting, I spread Preen on top till I was ready to get my bulbs,peony and siberian iris in it and am now wondering if that was a wise thing to do. Will Preen adversely affect them since I spread it on top before I planted?

I don't see how, Julia. Preen prevents germination -- and doesn't affect existing plants.

I would be most concerned about the peony roots. Clear off the existing soil and bring in some that is uncontaminated for the peonies. You don't want the preen getting down by the roots which will be planted shallowly. Preen can cause some root pruning, or in other words, slow down growth of roots, and now is the time you want those peonies growing the new roots.
Preen is marketed as an inhibitor to seed germination, but you don't want it touching any roots, and peony roots may be shallow, or you may be stirring the preen deeper when you plant. Does that make sense?
The best way to handle new beds is weed them, (till or kill) then plant, then spread the preen.

Maybe Polly will come on here and advise you on the siberians. The bulbs will be fine.

Siberians will be absolutely fine. I use Preen in all my beds.

Never knew that, Cindi.

I used to put Preen (actually the landscaper equivalent) the way Julia did- before and after planting. My boss at the time saw that, blew up at me, and sent me to applicator training. They warned about the root-pruning effect. It's the reason the bags warn not to use it more often than every 90 days.
i think established plants could handle it accidentally touching the roots, but anything newly planted this time of year is going to have roots in active growth phase, and that will be retarded. I know it is not supposed to act as a growth retardant,....but it can. Won't kill the plants, but it won't do them any favors, either.

Thanks for the info. I guess the 90 day schedule is about what I use. First thing the end of April/ first of May, and then when I replant and get the soil stirred up.

Great information.....

So if I don't spread the Preen down into the soil, I should be fine for the siberian iris and peonies?

Oddly, when I checked the Preen.com site they said that Preen was not compatible for crocus or daylilies. I posed a question on the AHS Robin (Daylily group)forum regarding other gardeners experience with spreading Preen with daylilies since the Preen site said daylilies are not compatible either with Preen. I grow alot of daylilies so you can understand my concern.

I may end up with a dead garden next spring

Oh -- I hope not, Julia. Especially since I have my Daylilies mixed in with my Irises in several locations.

Polly -- I do the same thing -- plant my Iris rhizomes, then spread Preen, then water. I forgot to do that on a bed I planted in August -- I now have a bed full of annual weeds that will have to be hand-weeded. Can't take a chance on hitting the Iris leaves with Round-Up spray..............

I promise it won't hurt the sibs, I've been using it for so many years. Please let us know what they say about the daylilies.

On the Preen site it says daylilies ARE compatible with Preen. I know crocuses are such tiny bulbs it probably does inhibit them sprouting, like a seed.

http://www.preen.com/products/...

Thanks Polly. I appreciate the feedback on the iris.

I've spread Preen around my established daylilies for the last couple of years and have had no problems.

Me too.

So far it doesn't seem to be an issue with Preen around established daylilies that are already in the ground and keeping with the recommended dosage however there may be some cause for cautious when planting seedlings. Just advice I was given and I have no personal experience since I haven't used Preen on my newly planted seedlings.

I'll check peony forum to see if anyone has used it before they planted their bareroot.

Shoot!! I wish I had read this a month ago. I have a garden full of weeds around new iris plants.
I rely on annual poppies germinating in some areas so I dont Preen in that garden. Is it too late to Preen now? or doesnt it have any effect on established weeds that are blooming and about to set seed for next year? I am talking about the "sour clover " stuff that just grows everywhere.

No, It only works to kill seeds while germinating, won't work on the weeds themselves. Active life is 3 months for "flower" preen and 1 month for "vegatable" preen, so effect will be over before spring gets here. Can't think of the righht name of the weed you're talking about...light green ,3-leafed "clover" looking, small yellow flowers!? We've got it here also, call it "sour grass". Don't know why....doesn't look like grass? Anyway ,preen would be best used, in your case, early spring, before anything germinates....but....it will stop those Poppies,too!...Arlyn

Thanks for the info. I will apply in late April then.There is nothing growing.I dont sow poppies in that area.

Just remembered the rightname of that weed...woodsorrel...when I was young,never forgot anything..now that I'm old...can't remember anything !!...Arlyn

It IS Woodsorel.
I belong to a Communitu Supported Agriculture farm share group.
They had Woodsorel on the ptable as a freebie one week.
Its a huge long story but I will just say not all CSA's are created equal and this one will not have me as a member next year.