When planting lawns, the order in which you add fertilizer and seeds doesn't matter, but it's important to add fertilizer when planting your lawn. You can combine the fertilizer and seed and spread them together, or you can spread the seed and fertilizer separately, one immediately after the other. Most landscaping professionals agree that it's always best to fertilize the soil first if you're planting a new lawn. It is also recommended to perform a soil test to select the right fertilizer.
The results will determine the right levels of phosphorus, potassium and nitrogen for a healthy start to the lawn once the seeds have been planted. Apply starting fertilizer before sowing or laying the lawn, or after planting the new lawn seed. You don't want to apply it directly to the newly planted lawn or you can get burned. You can plant lawn seeds immediately after applying the fertilizer.
Please make sure that there is no weed control agent in the fertilizer, as this will also prevent the weed seed from germinating. Overseeding or replanting means spreading seeds on existing grass where grasses are too thin or areas of grass are empty and grasses do not grow well. It won't harm your lawn, but you may lack the necessary nutrients contained in a well-balanced fertilizer for ongoing lawn maintenance.