Ask Mr. Smarty Plants

If you have not already done so, please read our How-To Article Native Lawns: Buffalograss. It should answer several of your questions about filling in the grass and keeping weeds out. You are correct, as you will see in the article, in saying that the weeds seem to grow faster than the Bouteloua dactyloides (buffalograss). Not only do you need to keep the weeds out by hand-pulling, but you need to learn which is buffalograss and which is weed.  In particular, when reading the How-ToArticle, take note of the final section: "After You Plant."

The Lady Bird Johnson Wildflower Center recommends neither for nor against herbicides; however, in this case many of the "weeds" will be, like buffalograss, monocots or grasses. Some of those grasses will also be native, and therefore very vigorous. There are wide-spectrum herbicides that kill everything, including plants you probably didn't want harmed. There are herbicides for dicots, or broad-leaved plants, that should not harm the grasses, but, again, with a little breeze you can easily damage a tree or shrub or herbaceous blooming plants, all of which are broad-leaved, too. 

Also, as you read the article, you may realize that perhaps you have been over-watering the buffalograss; once it is established, it can get along without irrigation. The weeds, on the other hand, will grow even more happily and lush with additional watering. You will have to water the new patches until they are established, whether you seed or re-sod those bare spaces.

Bouteloua dactyloides

Bouteloua dactyloides

Bouteloua dactyloides

Bouteloua dactyloides