Topdressing with fertilizer is a bad idea. Sub-dressing is superior.
This idea was demonstrated clearly at the Mid-Florida Research and Education Center this week. Dr. Chris Marble, weed specialist, showed us many trials with pre-emergent herbicides and how various mulches affected weed growth. He concluded by showing how fertilizer placement makes weed growth worse.
The traditional way to apply slow release fertilizer is by sprinkling it on the surface of the soil. But some is lost by sunlight degradation and more can be lost by heavy rains. Another problem is that it feeds weeds and encourages their growth.
So, a wiser way to apply fertilizer is to fill the pot about half way up with soil, apply fertilizer, then fill the pot the rest of the way, then plant the new plant. The new plants roots will come in contact with the fertile area but the nutrients are out of reach of any weed seedlings.