To fertilize a potted plant, rather than sprinkle the fertilizer on top, stick your finger about halfway in the soil along the edge of the pot and pour some fertilizer in the hole, then cover it up. The roots will find their way to the plant food, and weeds that might try to grow on the top of the soil will not 'steal' all the nutrients. I use this method with timed-release fertilizer, which is particularly sensitive to sunlight, so it is much more effective when covered.