Determining which fertilizer to use depends on type of plant

Let’s take a little bit of time to discuss fertilizers since this is the time of the year that most of them are first applied.

Some basic rules of thumb in selecting the right fertilizer are associated with the numbers on the bag. All three numbers are important but the balance between the numbers on the bag have much to do with the type of growth you will see after applying it.

The first number represents the amount of nitrogen. High nitrogen is primarily responsible for encouraging leaf and stem growth. When you choose a fertilizer high in the first number you will encourage those plants which primarily need leaf and stem growth. Examples would be lawn grasses, ornamental grasses, trees and shrubs not selected for their flowering, leafy vegetables and the like.

Phosphorus, the second number, stimulates production of flowers, roots, fruit, seeds and oil.

As an example, let’s look at fruit trees and roses. You want leaf and stem production from both plants but you also are concerned with flower and fruit production. In this case, you might want a fertilizer that is high both in nitrogen and phosphorus, the first two numbers. On the flip side, those plants which you enjoy for leaf and stem production, such as many so-called nonflowering trees and shrubs, would need a fertilizer high in nitrogen but lower in phosphorus.

Once phosphorus has been put down for the season, it is seldom needed again that same year unless you have very sandy soils. It is very important to put phosphorus down in the backfill of a planting mix or near the root system during planting or transplanting.

The third number is potassium. Potassium is important for heat and cold tolerance, disease and insect resistance, and the general health and well-being of the plant. You should always try to put some potassium down nearly each time you fertilize and particularly just before periods of stress. Overapplying phosphorus can cause some problems if it is done over a long period of time but this is not true of potassium.

The amount and type of nitrogen fertilizer in the bag will dictate how much you can apply at one time. High-nitrogen fertilizers can cause immediate, severe damage to plants if overapplied or placed too close to stems or trunks. This is why the best fertilizers will have half of their nitrogen in a slow release form or an organic source so all of it is not released at once.

Fertilizers are carried to the roots through the soil by water movement. If fertilizer is not wet, it will not dissolve and it will not enter the roots or the plant. Place fertilizers close to the source of water but not physically close to the main trunk. Let the water from the irrigation move the fertilizer to the plant’s roots for you.

Nitrogen fertilizer is the first fertilizer to be lost after application and this fertilizer may need to be reapplied during the growing season on plants that need continuous growth. These would be plants such as annuals, herbaceous perennials and most vegetables where you want a constant flush of growth through the growing season. Most woody plants do not do this and so you usually just fertilize these once or twice during the early part of the growing season.

Another ingredient to put down is iron. The type of iron is very important for many plants. Iron applied to the soil should be applied just prior to new growth and watered in so the iron is carried to the roots, taken up by the plant and is ready to move into new growth as it is developing.

Q: I have a few questions regarding fighting off borers on my trees. About a year ago, I used a Bayer’s product (Systemic I think) that you mix with water and apply around the base of the trees. In recent years, the borers have really hurt my apricot, plum and apple trees. Can you eat the fruit of the trees after this type of application? Should this process be repeated yearly? And finally, are there any other ways to control borers?

A: I have never used this product and I tend to stay away from what are called the hard pesticides whenever possible; I lean more toward organic controls as much as possible. This product is known in the commercial trade as Merit. I checked both labels.

This insecticide is recommended for a few fruit and nut trees. It is only labeled for pome fruits such as apple, pear, Asian pear and quince, and the only nut tree is pecan. It is not labeled for any stone fruits such as apricot or plum. You cannot legally use this product on those fruit trees. Please read and follow the label.

I suggest that you should not use any fruit from trees that are treated with pesticides not recommended for that type of tree. I would suggest that if you stop treating the trees for a period of 12 months, the new crop of fruit would be safe to use.

According to the label, you are free to treat and use the fruit from pome fruit trees such as your apple. However, in this case, knowing this is an insecticide that is systemic, I would not feel comfortable eating any part of the tree the year it was treated.

If you have any further questions regarding the interpretation of labels on agricultural products, you could contact our local office of the Nevada State Department of Agriculture or the manufacturer.

The best methods of controlling borers are to keep the tree healthy, prevent sunburn of limbs and branches by having sufficient canopy cover, and applying a whitewash to the main trunk and major scaffold limbs.

Merit has been shown to be an effective and safe insecticide for controlling many types of flat-headed and round-headed borers when the label has been followed. The label spells out how often you can use this product each year.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at extremehort@aol.com.

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