Fall lawn care is really about shoots and roots -- of both the turf and the weeds.

If you do nothing else to improve the quality of your lawn -- besides keeping it watered and mowed, fertilize in September. In September, cool-season grasses start a flush of growth and begin preparing for winter by socking away nutrients in their roots. By fertilizing now, you really can get the most return on your investment.

Fertilizing later in the fall (mid to late November), when the top growth of the cool-season turf grasses has nearly stopped, will favor rhizome growth resulting in a denser turf. Anything that will promote proper turf grass growth will ultimately help minimize weed populations.

Fescue and bluegrass are the top cool-season lawn turfs. When they are healthy, they are generally at their best for long-term weed control. Unfortunately, sometimes we are fooled into thinking that we have lush-looking lawns. In reality they are often a mix of equally healthy turf and weeds. When heat and drought are added into the equation the weeds tend to get a foothold in the thinned and sometimes killed areas that develop in our cool-season turf.

September is also the Number #1 time to seed or overseed cool-season lawn turfs and it also begins the year’s prime time to control perennial and annual cool-season weeds. Lawn owners now are faced with a decision –do I need to reseed some areas or overseed other areas or am I better off providing weed control. For lawns that are thin and weedy, these September activities can conflict. There are no easy answers for this situation. You need to decide on the best approach for your particular situation.

Let’s look first at the type of lawn that you might have. Bluegrass can spread a bit on its own. Fescue however is much slower to fill in, so seeding or overseeding often is the only real answer for bare spots or thin lawns. Seeding however can throw a fall lawn schedule into disarray.

For those lawns that are mainly weeds, the time for complete renovation is now. Renovation means killing all existing vegetation and starting over. Finally, one needs to consider seeding restrictions because herbicides are selective only in established lawns. Do not apply broadleaf herbicides within 4 to 6 weeks before seeding and not until the new grass has been mowed several times. Therefore, if overseeding is currently being considered, one should avoid using these products.

If you need to overseed your lawn this September, you might consider using a starter fertilizer and plant as soon as possible. Then hope the new turf will have grown enough for you to apply a weed-and-feed product later in the fall. Fertilizers formulated for established lawns can burn tender turf seedlings. Many broadleaf weed herbicides will kill the sprouting turf. In fact, the best guideline is not to apply any herbicides or fertilizers (for established lawns) until newly planted fescue or bluegrass has grown enough to merit mowing two to three times.  

(SDSU recommends fertilizing established fescue and bluegrass lawns with 1 pound actual nitrogen per 1,000 square feet in September. Then apply another pound of nitrogen in late October to mid-November.)

If the fertilizer product you’re thinking of using has other ingredients -- broadleaf weed herbicide, for example -- you need to read the label carefully! Look to make sure that it is the best product to use for your purposes and that it actually contains the amount of nitrogen you need.

Weed control in fall can basically address three types of weeds:

·         Crabgrass, goosegrass, foxtail and other annual grassy weeds. Most of the crabgrass is now producing seed and nearing the end of its life, (as soon as the first hard frost happens). Therefore, try to keep seed production to a minimum by mowing regularly and make a mental note about applying a preemergence herbicide next spring in heavily infested areas.

·         Winter annual weeds, such as henbit, chickweed and speedwell. They “may not look impressive above ground”, are establishing an extensive root system that helps them get off to a quick start the following spring. These weeds can sprout any time from August to November, so if you wait until mid-October or later to treat dandelions, you’ll also control most of these winter annuals. It’s one way that you can “kill two birds with one stone!”

·         Dandelions and other cool-season perennial weeds. They are beginning a growth flush and are storing nutrients in their roots. If applied in the fall, broadleaf weed herbicides have a chance to kill their tough root system, as well as their leaves. Control of broadleaf weeds in the fall (mid-September to November) gives the turf grass an opportunity to fill in the open areas that appear after weed control. This will result in a denser turf which culturally helps prevent weeds from becoming established.

There are a number of postemergence herbicides available for selective control of broadleaf weeds. Most of these products are two-, three-, and even four-way combinations of 2,4-D, and either 2,4-DP, dicamba, MCPP, or triclopyr. These combinations have taken most of the guessing out of broadleaf control because broadleaves not controlled by 2,4- D are usually controlled by one of the other herbicides. For example, 2,4-D provides excellent control of dandelion and plantain, but provides poor control of white clover or red sorrel. Dicamba, on the other hand, provides excellent control of white clover and red sorrel and only fair control of dandelion or plantain. By applying a combination of these two, all four weeds will be controlled.

This doesn't mean that a combination product will successfully control all of those unwanted broadleaf weeds in your turf. A few broadleaf weeds are just naturally hard to control with the current herbicide choices, and secondly, the wrong combination product may have been chosen (i.e. 2,4-D + MCPP instead of 2,4-D + MCPP + dicamba). So it is still important to identify your problem weeds before you try to chemically control them.

A September application of a (broadleaf) weed-and-feed product will fertilize the lawn and control many dandelions. But, fertilizing in September and applying herbicide separately in October often provides better results. Dandelions usually develop a new “crop” in late September or early October. One thing to remember is that you can spot spray weeds any time, so long as they’re still actively growing.

As we approach this fall, don’t ignore your lawn. Remember good cultural practices are also important. Proper mowing, watering, aerifying compacted areas and other sound management practices should help establish a thick, healthy lawn. A dense stand of grass provides few opportunities for unwanted weeds. Good cultural practices, along with an occasional application of a broadleaf herbicide, should effectively control most broadleaf weeds in the lawn.