....can be expensive and in many cases 'unnecessary to purchase/plant'. Soils which are poorly arable are great places for weeds. Class 6 (many old pastures/brushy fields) or class 7 (timbered) are good places to create a soil disturbance (prescribed fire, TSI, light discing, mob grazing etc) and glean the benefit of natural succession with a plethora of weeds ensuing for deer to browse. Deer are highly selective and tend to browse the highest quality weed parts.
This link gives CP, TDN, and mineral content of native plants consumed by deer in a 2-3 yr study period.
QUALITY OF NATIVE PLANT FORAGE SPECIES IMPORTANT TO WHITE-TAILED DEER AND GOATS IN SOUTH CENTRAL OKLAHOMA
Mileage may vary in the weeds deer consume in other areas!
Just remember the two prerequisites for weed seed germination from the soil bank are: 1) direct sunlight exposure and 2) optimum soil temperature. Don't forget the importance of woody cover and tall NWSG to compliment the food source.