Trees such as American Sycamore grow best if they are fertilized lightly in the spring once frost has passed with a well-balanced, extended-release, fertilizer such as espoma Tree-tone. Fertilize American Sycamore again 6 to 8 weeks later to encourage denser foliage or faster growth of young trees. Either chemical fertilizers or organic matter can be used successfully with American Sycamore Tree. Since an organic method of applying manure and/or compost around the roots, produces excellent results and also improves the condition of the soil, this would be an excellent first line of attack. Organic additions to the soil can also be combined with a shot of chemical fertilizer for maximum effect. If chemical fertilizers are used on your American Sycamore Tree, applying a slow-release, balanced fertilizer once a year is probably the simplest solution. There are many slow-release fertilizers on the market. If you can find a fertilizer formulated for shrubs and trees, this fertilizer would work well on American Sycamore Tree. However, slow-release is certainly not the only way to fertilizer trees such as the American Sycamore. A less expensive fast release fertilizer such as a 10-10-10 will work just as well if applied twice during the early spring and early summer. If you are looking for a fertilizing routine tailored to your specific conditions, a soil sample should be taken and the fertilizer and trace elements matched to the needs of your soil. Don't fertilize American Sycamore after August. Fall is the time for plants to begin preparing for dormancy. Fertilizing at this time may stimulate new growth that will be too tender to withstand the winter. In the South, a late May application and another in July would be about right. More northern areas may wish to fertilize only once in June or July. The amount of chemical fertilizer used per plant will vary with the size of the plant and it's root system. (Use less fertilizer for gardenias in a container.) Over-fertilization can be much more detrimental than under-fertilization. "Fertilizer burn" can occur when too much fertilizer is applied, resulting in a drying out of the roots and damage or even death of the American Sycamore. It is much, much better to err on the side of too little fertilizer than too much. When roots are burned, the first sign is often scorched looking leaves. If over-fertilization is severe, the plant may just wilt and die. If you are a beginner at growing plants the American Sycamore Tree is one of the easiest trees to grow however it may be helpful to know that a very small plant which is planted in the ground will take about 1/8 - 1/4 cup of fertilizer. A very large tree in the ground will take 2 - 3 lbs spread around the drip line of the branches (not next to the trunk). This is a very loose estimate, so please read the directions on the fertilizer before applying it. Never fertilize a plant with a chemical fertilizer if the plant looks sick or wilted. If a plant is struggling due to a disease or root problems, the fertilizer will only add stress to it's life. Try to cure the problem before adding fertilizer.