NEW YORK (This Old House) - Fall is here and it's time to fertilize. Why now? Taking the time to fertilize in the fall will strengthen your plants' and lawn's roots, giving them a strong base on which to thrive next spring.
The first thing to understand about fertilizer is the formula, which is represented by three numbers, such as the common 5-10-5.
The first number represents nitrogen, which promotes lawn blade and foliage growth.
The second number stands for phosphorus, which helps root growth.
The third stands for potassium, which promotes cell function and absorption of trace elements.
But what do you fertilize? When? And with what? Let's start with your lawn.
Early in September, grass is recovering from a long hot summer and may be coming out of a drought-induced dormancy, so you'll want to give your lawn a shot of nitrogen to push blade growth.
A fertilizer with a formula of 20-8-8 will get it growing again. Always follow the manufacturer's recommended rate of application. Some people treat weeds and insects at this time, but I think that unless there are signs of trouble or a history of problems, don't apply anything but fertilizer.
While this September dose of fertilizer is important, an application at the end of October or early November is essential. At that time, apply a fertilizer with a formula of 13-25-12.
The push of phosphorus will stimulate root growth through November and even into early December. By helping roots grow before winter sets in, you are insuring that the lawn will green-up quicker in the spring and become more resistant to disease and draught.
With the lawn taken care of, it's time to consider plants. By now, perennials are starting to fade but they will benefit from 0-20-0 super phosphate fertilizer scattered around the plants at recommended doses and lightly cultivated into the soil. Next spring you'll have stronger plants with more flowers.
Fall is also a great time to fertilize shrubs and trees. In my opinion, all trees and shrubs need fertilizer, because most of them are located in mulch beds that use up nitrogen as they decompose.
In addition, every fall we rake leaves off these beds, depriving plants of the nutrients that decomposing leaves would traditionally release. To compensate, I recommend applying one to three pounds of slow-release nitrogen per 1,000 square feet of bed and cultivating lightly. (To figure out the exact amount of fertilizer you'll need, calculate the square footage of your beds and consult with your local garden center.)
I prefer fertilizing trees in late September and early October to promote root growth. These nutrients will still be in the soil come spring when plants start to grow. If you have a tree or shrub that does not flower well, a dose of super phosphate will help promote flower growth.
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However, if the plant is not located in the right spot, all the super hosphate in the world won't make it flower.
Fall is also the time to plant bulbs. I prefer to use super phosphate to promote root growth, insuring strong flowering in the spring. Some people recommend using bone meal when planting bulbs but I find that it attracts rodents who eat both the bone meal and the bulbs.
As you can tell, the basic goal of fall fertilizing is to promote root growth. When you have strong roots, you have healthy plants with numerous flowers. So push those roots!