Too Many Plants, Not Enough Nutrients In natural landscapes, plants reach a equilibrium of plants per acre eventually. Leaves and stems fall to the ground and decompose releasing their nutrients into the soil to become fertilizer in a balanced nutrient cycle.

In landscapes however we often plant more plants than the carrying capacity of the soil. We gardeners cram as many plants as we can into our gardens. Landscapers maximize plants on new builds. Eventually these plants grow and use up all of the nutrients in the soil. This is why we need to fertilize landscape plants annually, especially in older plantings. Shrubs and trees need proper nutrition throughout the growing season to remain healthy and vigorous.

How Often Should We Fertilize Landscape Trees and Shrubs? We recommend applying fertilizer at two to three times during the growing season for actively growing shrubs. For example, for a thrice annual routine, the first application of fertilizer should be in March, the second in May and the last application in July. In certain situations, a final light application of low-nitrogen fertilizer such as 0-5-10 can be applied in early September to ensure that your shrubs are well nourished through the fall and winter months.

What Kind of Fertilizer? The best fertilizer materials for shrubs are 4-1-2 or 3-1-2 ratios. This would be an analysis such as 16-4-8 or 12-4-8. The analysis is found on the fertilizer bag or box, the three numbers referring to nitrogen, phosphorus and potassium respectively. We suggest using these ratio-type fertilizers because shrubs use a large amount of nitrogen but they don’t need a lot of phosphorous since it accumulates in the soil. However, if the above analyses cannot be found, then you can still use a general-purpose fertilizer, such as 10-10-10.

How Much Fertilizer? The rates for each application should be two level teaspoons per foot of height if you are using the 12-4-8 or 16-4-8 materials or one level tablespoon if you are using a10-10-10 fertilizer.  When you purchase the fertilizer make sure it is not a weed-and-feed formulation that contains a post-emergence chemical that kills weeds. Weed-and-feed products that contain post-emergence herbicides can injure plants if applied to shrubs and flowerbeds.

Slow Release Fertilizers? Also, note if the nitrogen component of your fertilizer is all or part slow-release. If it is a slow-release material, be certain to follow all label directions. Make sure that you do not exceed the recommended rates. This is especially important since the danger from salt injury is particularly great during the hot summer months.

How To Apply Fertilizers When applying fertilizers, broadcast the desired amount evenly over the root system out to the ends of the branches rather than placing the fertilizer in only one or two spots. This allows for even root uptake and helps to avoid concentrating the fertilizer material, which can then result in root damage or death. There is no need to remove the mulch material, such as pine bark or pine straw as the fertilizer nutrients will wash into the root zone. After applying fertilizer, you can water it in to speed up uptake.