Wherever there is no competition, ragweed takes hold quickly. There aren't many types of soil that it doesn't grow in. You find it around sidewalks, streets,rock piles, construction sites, in vacant lots - pratically any dry sunny spot. Hay fever is no rose garden for those who suffer from it. Hay fever costs a lot in terms of health care.
Prevention is the way to nip hay fever in the bud.
First you need to eradicate ragweed or keep it from getting a foothold. Once this is done, you can try to improve the soil to encourage the other species already present. Another solution that is effective, economic and attractive is to sow new plant species that will compete with ragweed. As long as ragweed plants remain, people who are sensitive to the pollen will have to get treatment and medication to relieve their symptoms. If there are just a few plants, simply pull them up as you pass by.