: Now's the time to fertilize

By applying fertilizer high in nitrogen just before the spring growth flush, you can double, even triple the new growth on your landscape plants. With fertilizer, a young tree can extend its branch spread an extra 12 to 28 inches over those not supplied nitrogen through fertilization.

The same is true for shrubs, and an even greater increase in size can be achieved with vines and ground covers.

With our recent late-winter heat wave, our spring growth flush is likely ahead of schedule. However, even if new growth has begun on your landscape plants, they'll still benefit from increased growth with fertilization now. Nitrogen-fixing leguminious trees such as mesquite, palo verde and acacia also will reap the benefits from a season-starter application of nitrogen.

Any fertilizer containing enough nitrogen can be used as a season-starter fertilizer. Nitrogen is the first of three numbers on the fertilizer package.

When possible, choose a fertilizer with a higher percentage (number) of nitrogen than of phosphorus, the second of the three, and of potassium, the third. It's nitrogen that stimulates new leafy growth and shoot elongation. In fact, to stimulate spring growth of landscape plants, you need use only nitrogen (N). No phosphorus (P) or potassium (K) need be in the fertilizer.

To my knowledge, only one is nitrogen-only, and that's ammonium sulfate. It contains 21 percent N and no P or K. It's the least-expensive source of nitrogen and is available at most garden centers and home-supply stores. Just look among the granular fertilizer products sold in bags.

If you use ammonium sulfate (21-0-0) or another type of fertilizer with a similar level of nitrogen (give or take 5 percent) here are the amounts to use for:

• 1 pound or 1 1/2 cups of ammonium sulfate (or similar fertilizer) for each inch of trunk diameter measured 18 inches above the ground.

• 1/2 cup of ammonium sulfate (or similar fertilizer) for shrubs under 3 feet in size.

• 1 cup of ammonium sulfate (or similar fertilizer) for shrubs over 3 feet.

• 1/2 cup for plants 3 feet or less in diameter.

• 1 cup for plants greater than 3 feet in diameter.

• 1/4 cup of ammonium sulfate (or similar fertilizer) for vines 10 feet or less in length.

• 1/2 cup of ammonium sulfate (or similar fertilizer) for vines more than 10 feet in length.

When fertilizing, keep in mind that the roots of landscape plants grow well beyond their branch ends. Roots of mature trees can spread out two to four times the spread of their branches. The roots of shrubs can grow many feet beyond their branch spread. The same is true for vines and ground covers.

Keep this in mind when applying fertilizer. Scatter the fertilizer evenly over a good portion of the root system. After application, water the fertilizer in with a slow, dripping, porous soaker hose or fan-type lawn sprinkler.

if you go

"Container Plants for Your Patio Garden" will be the topic of this week's gardening demonstrations. Presentations will be at 1 p.m. Wednesday at the Wilmot Library, 530 N. Wilmot Road; and 1 p.m. Friday at the Oro Valley Public Library, 1305 W. Naranja Drive.