I plan on planting saint augustine plugs this spring. If I use this first will it prevent the plugs from spreading or growing roots?

Thank you for your question regarding Scotts WeedEx Prevent with Halts. You will need to wait until the new grass has been mowed 4 times before applying this product. If WeedEx is applied first, you will need to wait 5 months before plugging. We would be more than glad to recommend you a product that will better suit your needs. At your earliest convenience, please contact us at http://tinyurl.com/mds8zo5.