Tips on fertilizing established perennial beds
Posted on: November 25, 02
Established perennial beds should be fertilized in early spring, if necessary. A soil test is the best way to find out what type and amount of fertilizer to use: many garden centers offer a soil testing service, or they can refer you to local soil laboratories. I generally recommend a product higher in the middle number: this is phospherous, which helps to promote strong stems and plenty of flowers. A formulation like 5-10-5 is suitable for perennials, in most cases. Buying fertilizers in larger bags is usually more economical than smaller bags or boxes. In my region, the best buy is often big bags of all-purpose vegetable garden fertilizer.
Some experts recommend about 2 pounds of actual nitrogen per 1000 square feet of bed each year. To calculate how much fertilizer you need, first measure the square footage of the bed. Then use this formula:
(square feet of bed ÷ 1000) × 2 pounds = number of pounds of actual nitrogen required.
An example: a 250 square foot bed
(250 ÷ 1000) × 2 pounds = .5 pounds of actual nitrogen needed.
To calculate how much actual nitrogen is contained in a fertilizer, use this formula:
Pounds of fertilizer × percent nitrogen (the first number on the bag) = pounds of actual nitrogen.
For example: a ten pound bag of 5-10-5 would work out to:
10 pounds × 5% = .5 pounds Nitrogen per bag. One bag happens to be exactly the right amount to fertilize the 250 square foot bed calculated above.
Granular fertilizers come in two main types, quick-release and slow-release.
Quick-release types can easily burn the foliage of new plants, since they are high in salts. Careful application is necessary, and the product should be sprinkled around the clumps rather than right on top of them.
Slow-release products are much less likely to burn, but care should also be taken to spread them around plants rather than on top. These products release nutrients over several months, giving a more even level of food to plants throughout the growing season.
Incorporating granular fertilizers into the ground will get the nutrients closer to the plant roots. Established beds cannot be easily dug over, but a claw-type hoe is useful to work the fertilizer granules into the top couple of inches of soil.
Liquid fertilizers are applied either with a watering can or with a hose and siphon applicator system. Gardeners often overdo these products, when it comes to perennials. Choose a fairly low formulation (like 5-10-5), and one that is highest in the middle number (phosphorous). High nitrogen products may cause lots of floppy, lush growth at the expense of flowers.
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