Yikes. Depending on which broad leaf weed killer it was, if it was designed to be eaten by horses/cows and then they poop it out to reapply it, that stuff persists for years. Using the grass in your garden as a mulch or soil amendment can make it unusable for up to FIVE years. That is why I won't be applying bunny gold (I'm babysitting some bunnies) to my garden because I cannot be certain that weed killer was not used on their packaged orchard grass and timothy hay. 🙁
I had to stop growing vegetable crops here at our current home due to the fact that this 22 year old entire subdivision ( over 100 homes) was built on a swamp land. (I gardened organically at our Cal. 20 acre horse ranch). The developer brought in truckloads of soil as fill in order to build homes. It seems that each truckload contained different types of soil. After 2 years of utter crop failure, I decided that it wasn't worth the time and labor to continue. I brought in 32 tons of boulders (each 200- 700 lbs) from Mt. St. Helens eruption , as well as many tons of river rock to line a new meandering stream ( from the far end of the back yard flowing to the front yard driveway /sidewalk)that I dug and used the dirt to create raised beds formed by the boulders. We live at the end of a cul de sac which continues to a 2 block street , then ends at another cul de sac. During late autumn/ early winter winds blow the fallen leaves right onto our lot. So we have tons of leaves . The foot high leaves have now broken down to an inch or two... so organic ? soil... I can't attest to this as I do not know what all of these neighbors spray or use on their lots. I also got lawn clippings from 4 neighbors , however these neighbors have sold their homes and the new neighbors only put their lawn clippings into the recycle bins ( garbage cans for pickup). So, I grow 19 Japanese maples, many mugo pines + dwarf mugo pines( pruned into bonzai shapes), many coral bells, and 9 types of ferns in shade provided by the maple trees. I grow many types or native plants and other flowers,but these have drowned this past Jan. heavy rains ( even on top or the raised beds). We had lots of robbins to eat worms, but 2 years ago they stoped showing up as they were replaced by many moles ( very destructive to ferns and coral bells' root systems ) here and neighbors lots. I hope that this answers your question. I am looking for information as to what direction to continue landscape garden in.
Go for it in spades , I have nothing to loose here but everything to gain ( keep in mind that I DO NOT want to increase the mole population as they burrow through fern roots and kill them) .......
On our Cal. ranch, our front yard was over an acre. When we had a drought and killed the grass, I let it stay dead. I gave away the lawn motor. I then used a tractor to disc the former lawn all winter and spring to kill off any sprouted seeds, then I planted alfalfa instead to supplement feed the horses in the barn ( 9 horses). Mares and foals (11mares +foals )had 15 acres of pasture (timothy, bermuda, oats, barley, 3 types of clover). I used horse manure ( 3 heaping wheel barrow fulls /day from the horses in the barn and corrals) to fertilize it as well as my garden area which were VERY productive. Now , due to my health issues, my doctors ordered a mostly protein diet ( meat, fish, ) with very few carbs. Minimal pastries, candy etc. as treats only. I have NO lawn here, just the trees, ferns,azalias, corral bells, and ornamental stepable thyme ground covers. Most of the flowering plants as well as the so called "native plants " have drowned due to heavy rains last Dec. and Jan. .
Alasgun... I built 7 raised beds of varying sizes using 200- 800 lb. boulders as retaining walls. No cement was used to hold them in place. I filled them with dirt that I dug to form a meandering creek bed, then amended them with peat moss, fine mulch from forest floor, horse manure , lawn clippings, tree leaves, and wood chips. I planted veg crops and strawberries. They started to grow extreamly well ,worms galore. Local Robbins raised 3 sets of nestlings. Then we had heavy rains for 2 days straight that drowned my garden plants. The State owned drainage canal right behind our back fence became a raging torrent. Enter the moles to escape drowning and started to dig tunnels and feast on the worms , then reproduce. We had tons of slugs and snails. Enter garter snakes that ate them and reproduce too. After 6 years, there are virtually no worms and slug and nails. The next year, more heavy rains, drowned my new planted veg. crops. The mole hills increased in these beds that made the soil look like a newly plowed field. So, I consulted with a state master gardener who recomended to plant native plants... I did... but 2 years later, a wind storm + heavy rain destroyed the native trees and the water drowned native shrubs and flowers. So, I planted J. Maple trees and in 3 years they produced lots of shade ... I then planted several types of ferns and other plants from all over the world. Result of this is that my landscape garden was on Clark County Garden Tour for 5 years in a row.
Then, right after Christmas last year, I became quite ill with covid... today, I get around using a walker and crutches. I work in the garden sitting on a steel folding chair so that I can reach small weeds that dare to sprout. I haven't seen a " lawn python " for several months, but the moles are still here and tunneling trough the ferns and azalias,making them wilt, then die. So, the short answer to your question is now - no. 
I still would like to continue to post our good and bad gardening experiences so that everyone can benefit from them. 
