When should I fertilize my shrubs?

ASK THE HORT AGENT

Question When should I fertilize my shrubs?

Answer Adding fertilizer prior to leaf development may be inefficient. Low absorption and spring rains can result in nitrogen loss.

In general, the best time to fertilize is when a plant is actively growing. To determine a specific time, pick a specific plant. Most landscape plants begin visible growth in mid to late April. Visible growth includes flowers, leaves or shoots.

Prior to visible growth, plants grow roots. While roots absorb water and nutrients prior to leaf growth, they kick it into overdrive after leaves pop out. Leaves release water into the air. As water is lost from the leaves, it creates a pull through the plant that sucks in more water through the roots. Think about drinking a milkshake through a straw.

By late to mid April most landscape plants have popped out. This is the best time to add fertilizer. Be careful not to throw fertilizer on the tender new foliage. A second application of fertilizer about 6-8 weeks later will keep your plants going into the summer.

Slow-release fertilizers are the best way to reduce nutrient leaching while simultaneously eliminating the need for a second fertilizer application. Slow-release (or controlled-release) fertilizers release their nutrients over an extended period of time using one of three methods:

• Material which dissolves slowly, such as granite meal or rock phosphate.
• Organic material broken down by microorganisms, such as manures.
• Nutrients coated with resin or sulfur which controls the release from the granules.

Slow-release fertilizers cover a range of time. The “coated” products are the most precise at predicting the timeframe when the nutrients will be released. A 30 to 60 day product is best for landscape use. Products releasing nutrients 90 days and longer may create new flushes of growth too late in the growing season. These late flushes may delay dormancy or be damaged by early frosts.

Prepare yourself for sticker shock. All fertilizers have shot through the roof. The days of cheap 10-10-10 are gone. Slow-release fertilizers have always been more expensive than regular, water-soluble fertilizers. If you are worried about pinching pennies and you want to know how to compare fertilizers, visit http://extension.unh.edu/resources/files/Resource000494_Rep516.pdf While slow-release fertilizers cost more initially, they save time and nutrients.

For more info about fertilizing trees and shrubs, visit http://www.clemson.edu/extension/hgic/plants/landscape/trees/hgic1000.html If you don’t have internet access, then contact me at 910-893-7530 or gpierce@harnett.org

Since we have fertilizer figured out. Let’s start working on that slow-release chocolate milkshake.

Gary L. Pierce

Horticulture Extension Agent

Harnett County