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If you know
that you have a problem with the annual weed, crabgrass, then fertilization in
spring should go hand in hand with the application of preemergent herbicides.
As their name suggests, preemergent herbicides address weed control not "after
the fact," but before their seedlings can even emerge. Preemergent herbicides
accomplish this by forming something of a "shield" that inhibits seed
germination.
Don't undertake the core aeration task discussed on Page 1
after applying preemergent herbicides: to do so would be to "puncture" this
shield, thereby decreasing its effectiveness.
Crabgrass begins its
assault on lawns in spring, when its seeds germinate. In fact, my suggestion on
Page 1 that overseeding be carried out in autumn, rather than spring, is based
in part on the threat posed by a spring crabgrass invasion. "So why not just
begin by killing the crabgrass first with a preemergent herbicide?" perhaps you
ask. Well, the trouble is that most preemergent herbicides work against not
only weed seeds, but grass seeds, as well!
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You can appreciate the
dilemma here. Overseeding is incompatible with the application of most
preemergent herbicides. Yet, faced with competition from crabgrass in spring,
you may find it difficult to establish your new grass. So while it's still
possible to overseed in spring, it's simply easier to do so in fall. There will
be no competition from crabgrass then, because the fall frosts kill off
crabgrass.
If you must overseed in the spring, look for a product
called, "Tupersan." Unlike other preemergent herbicides, Tupersan will not
damage germinating lawn grass seed. But if you're committed to staying away
from chemicals altogether in your spring grass care, postpone overseeding till
fall.
Article provided by:
http://landscaping.about.com
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