Pre (before) The Weeds Emerge, Pre emergent

Preemergent is a pretty popular buzz word when talking about lawn care.  Everyone knows to put down preemergent and most people know it goes down in spring.

 But do you know the weeds preemergents prevent?

Do you know how preemergents prevent weeds?

Do you know the weeds preemergents WON’T prevent?

That’s what I’m here to tell you – preemergents: the good, the bad, the ugly.

Preemergents Prevent Some Weeds But Not Others

Preemergents work by establishing a vapor barrier in the upper parts of the soil.  This vapor barrier can have a few different modes of action in preventing weeds.  The two most common products work by 1: inhibiting shoot growth and 2: inhibiting germination.  As you can see, they work by affecting a weed seed in one fashion or another.  What a preemergent does NOT do is affect an actively growing weed.  That’s right, if you have a lawn full of weeds and you apply a preemergent, you will be very disappointed with the results – nothing will happen in the short term! A post-emergent weed control is required to control an actively growing weed. So why apply a preemergent?

You apply a preemergent in the late winter/early spring to prevent summer annuals from growing.  On the flip side, you can apply a preemergent in late summer/early fall to prevent winter annuals from growing. But remember, preemergents do not know the difference between fescue and henbit, therefore any preemergent applied in the fall will affect your weeds and your over seeding.

Preemergent Was Applied, But I still Have Weeds

Oh boy, preemergents have even more pitfalls.  So preemergents work on annuals, that being said, what if you have a lawn full of perennials?  That is a whole new issue in itself.  Annuals live and die with the season changes.  Perennials are always alive, only sometimes being in a dormant state (think bermudagrass turns brown in the winter).  So therefore any preemergent applied will not prevent a perennial because it is never dead and regrowing from a seed – it is simply dormant awaiting to green up again.  Weeds like dallisgrass, broomsedge, and nimblewill have a tough reputation, often times because people do not understand that preemergents will not prevent them.  Other weeds with tuber like qualities: sedges, Virginia button weed, and wild violets, are also not affected by preemergents.  With all this bad news, is it even worth applying a preemergent? Absolutely!

Preemergents Save The Day

Some of our most aggressively spreading and growing summer weeds are summer annuals.  A lawn without a preemergent applied in spring is 100% guaranteed to have an infestation of crabgrass and other broadleaf weeds.  The other great thing about preemergents is that they do a phenomenal job of preventing those weeds from creeping in from your neighbor’s lawn.  You know, the neighbor that never does anything to their lawn – except mow it twice a year? That’s right, no more worrying about their junk slowly making their way into your lawn!
Preemergents are an important part of preventing weed infestations. Choosing the right pre-emergent can be a major step in having a clean lawn over summer.