Osmocote or similar coated slow release N,P,K fertilizers work best. For example, even though on the bag, Osmocote 18-6-12 says 8 to 9 month release, on or in the soil, this product will slowly release nutrients for two growing seasons. The reason is that Osmocote and most other coated slow release products release based on temperature and the calibrations are for when they are used in above ground containers. Because on or in the soil is much cooler than a container, the release of nutrient is much slower and therefore over a much longer time. This also means that more is needed to be applied initially since it is slower and releases over a longer period of time. Not only is the slow release desirable and little if any is lost to leaching, it is very safe and one has to nearly mulch a young plant with Osmocote in order to cause injury or burn. Osmocote and similar products are more expensive, but in light of the safety and you only need to do it once for the growing season, in my opinion, they are worth the extra cost. This is what I use personally when planting individual items in the field or landscape. I typically apply about 1/4 pound over an area about 2 feet by 2 feet, because from my research roots will extend out much faster and further that is generally realized. And it is important to remember that when trees are grown in the green knit containers in the ground, root growth outward is not restricted initially. Only after the root has grown out and is absorbing nutrient and increases in diameter, does the girdling occur at the small openings to block most of the sugars from the leaves from going back out to the root tips. I describe the roots outside the fabric wall as nurse roots, they contribute substantially to growth of the young tree, yet when the tree is harvested and transplanted elsewhere, the loss of those outside roots is of minor consequence. Organic fertilizers are also good. Organic fertilizers cover a huge range and some are very good products and others are of minimal value. They are quite safe and it is difficult to damage or burn a young tree with organic fertilizers. The organic fertilizer I have had the most favorable experience with is Milorganite. This is a modified sewage sludge out of Milwaukee, WI and is widely used by the golf industry on greens and tees because of the performance and safety. In this case follow the rate instruction on the bag. I DO NOT recommend using dry chemical quick release fertilizers on small trees as it is difficult to get the rate per unit of surface area correct. After applying the 100 pounds of nitrogen per acre rate in the field, then looking at the dispersal of the granules, it does not look like very much. And, as a result, when applying dry a chemical fertilizer around young plants it is tempting to apply more, since the proper rate looks like so little. Just last spring, because I was out of Osmocote, but a rain was forecast so I fertilized about 25 young pine trees 3 to 4 feet tall with the 28-4-5 chemical fertilizer we use in the field and proceeded to damage 11 of them because I applied too much relative to conditions at the time. In my case, I applied the fertilizer, the next day we got about 1/2 inch of rain which was enough to dissolve the fertilizer and move it into a limited volume of soil, then it turned off dry and it was 13 days before any more rain fell and these trees were located such that they could not be irrigated. The concentrated fertilizer caused a salt burn to roots near the surface as the soil dried out and caused partial defoliation --- and this is after conducting research in the area for nearly 50 years. So, yes, dry chemical fertilizers can be used, but be careful as it is very easy to get too much. Here at the research farm we do use a dry, quick release chemical fertilizer with analysis 28-4-5 but only on our field soils. This fits our needs well and has performed well in our field soils over the years. We broadcast this down rows of trees in the field in a band about 6 feet wide and at a rate of about 100 pounds of nitrogen per acre once in the spring and it lasts all season. This is because our soils have a hard layer down about 12 to 16 inches that makes drainage slow but adequate for the many species of plants we are working with. If soils are sandier and drainage is greater, applying the same amount per season, but applied in two applications would likely work better. Applying 100 pounds of nitrogen per acre of soil surface means spreading roughly 350 pounds of actual material out of the bag. With a fertilizer spreader that has been properly calibrated, this works well and requires a modest amount of time.