Ask Mr. Smarty Plants

First, we will have to say that we may not be able to give you the answer you are seeking. There is a good saying that we will use here. " There is no such plant as a weed, just a plant in the wrong place."  The best way to keep a plant from growing in an area is to dig it out. 

Always remove weeds when the soil is moist. It is a lot easier to get all of the plant and root matter out with loose soil.

Pay attention to what type of weed you find when removing. If you find the offending weed is spreading by root runners or rhizomes you will need to make sure that you are removing both plant matter and any underground roots or rhizomes. Once the roots are removed, a watchful eye should catch any new weeds before they have a chance to spread too much underground.

If you find that the roots are shallow and seem to not be spreading underground don't celebrate yet as this more likely is a weed that spreads by frequent seeding. For these you will also want to make sure to get out all of the plant matter and root. With diligent cultivation you should be able to control seedlings that propagated from seed left behind in the ground. Even if you remove the weed before it has a chance to seed (which you should), they will still come back from seeds that have lain dormant in the earth, or transported in by wind, birds and animals. Adding mulch to this process will help as the mulch will keep light from the underground seed, hindering its growth.  

If using mulch be careful that you do not have mulch along the base of the Dalea. Dalea frutescens is a woody shrub that will struggle if the soil or base remains moist. If you use wood mulch double check your mulch to make sure that it is drying out between rains. If not, limit the depth of the mulch as much as you can while still keeping enough to block out the sunlight for the weed seeds below the surface. If it suits the look of your garden you might want to consider using a layer of decomposed granite as a mulch instead of wood.

If you still are looking for annuals to add to the space take a look at Sally and Andy Wasowski's book Native Texas Plants: Landscaping Region by Region. Chapter four is titled Annuals, Biennials, and Short-Lived Perennials.

Bulbs in that area might also be a nice option as a companion for the Dalea. Scott Ogden's book Garden Bulbs for the South might give you some ideas. For both books, see Bibliography below.

Dalea frutescens