How To Fertilize And Water An Apple Or Pear Tree
This article was written for the backyard fruit gardener who has anywhere from just a few apple and/or pear trees to a small orchard in the backyard.

Though apple and pear trees can survive and produce fruit naturally in fertile soil, the two primary reasons for fertilizing them are to encourage growth, and to create healthier trees that will produce more fruit. That being said, there is often a temptation to over-fertilize in the hopes of producing an even healthier, larger or more productive tree. But be careful! If you force an apple or pear tree too far beyond its natural growth rate by over-fertilizing, you can cause it to grow too quickly. This can result in structural problems, weaken and predispose the tree to insect or disease infestation, and reduce tolerance to drought or temperature extremes.

So, to grow healthy apple and pear trees, where to start?

Evaluate Soil Conditions 

Before fertilizing your apple or pear trees, the best starting point is a soil test. Soil tests are done to determine soil pH and essential nutrient levels. Your local Extension Service might provide soil testing services or you can test soil yourself with a soil testing kit or soil pH testing probe. Once you know the soil pH you can adjust the pH if necessary to meet the needs of your trees. 

Soil pH is Important!

Apple and pear trees grow best in a slightly acid to neutral soil ranging from 6.0 to 7.0 on the pH scale. Soil pH is a measurement of the alkalinity or acidity of soil and is measured on a scale of 1-14, with 7 as the neutral mark. Any measurement below 7 indicates acid soil conditions, and anything above 7 indicates alkaline. 

If you're unsure about the pH of your soil, and whether or not it's suitable for growing apple or pear trees, it's a good idea to test the soil pH in the planting area. You can quickly test soil pH with a inexpensive soil test kit or pH tester probe. 

To raise the pH (make more alkaline) you can add pelletized limestone to the soil. To lower the pH (make more acid) you can apply Soil Sulfur, Aluminum Sulfate, or Chelated Iron. Adding organic compost to the soil or using compost as mulch can also help to increase acidity and maintain acid soil conditions.

Soil Nutrients

When selecting a fertilizer, the first question to answer is, "What type fertilizer do I need?" Determining what fertilizer to use can depend on existing nutrient levels in your soil. If you do a soil test, the fertilizer you choose can be based on the test results. 

The analysis on a bag of fertilizer, such as 10-10-10, represent the percentage (by weight) of the three major nutrients required for healthy plant growth. These three major elements are always in the same order: Nitrogen-Phosphorus-Potassium (N-P-K). Each of these nutrients affects plant growth differently.

The first number represents nitrogen (N). This element provides plants with the ability to produce more chlorophyll, which in turn sponsors more rapid growth to the part of a plant that is above the ground: the foliage. With each additional nitrogen application, plants should grow taller and greener.  Fruit trees require nitrogen for shoot growth and leaf production, which in turn influence the quantity and quality of the fruit. Typically, fertilizers that are high in nitrogen content are not recommended for use on fruit trees.

The second number represents phosphorus (P). Phosphorus aids in root development and therefore can help to increase bloom size and bloom production. Apple and pear trees have extensive perennial root systems that are usually able to absorb enough potassium and phosphorus from the natural supply in the soil. That being said, if your trees aren't flowering and fruiting well, and a soil test indicates a deficiency in phosphorus, you will  need to apply additional amounts of phosphorus to enhance bloom and fruit production.

The third number represents potassium (K). Potassium has many functions. It guards the plant against diseases and aids in drought protection and cold tolerance. It also serves a role in improving root development, and helps in the process of photosynthesis. If your trees aren't flowering and fruiting well, and a soil test indicates a deficiency in potassium, you will  need to apply additional amounts of potassium to enhance bloom and fruit production.
You might have noticed that all the numbers in the fertilizer analysis don't add up to 100 percent. That's because there are other nutrients and fillers often added to the mix. For example, specially formulated shrub and tree fertilizers will contain what is called a "micro-nutrient package." This package may contain other nutrients that plants, such as iron, sulfur, manganese, zinc and others. Other fillers might be included to help apply the nutrients more evenly over an area.

NOTE: The only true way to determine what fertilizer or nutrients are lacking in the soil is by way of a soil test. As mentioned, most states, and many counties, offer soil tests through their Cooperative Extension Service at no charge (or for a small fee). Or you can buy your own soil test kit. A soil test will indicate nutrient levels in the soil and pH. Based on a specific plants needs, this will help you choose the right fertilizer and other nutrients or minerals needed.

Fertilizing Instructions

Type of Fertilizer

As pointed out earlier, apple or pear trees planted in fertile soil may not require fertilization until they've used up many of the nutrients. The best way to decide on whether or not to fertilize, and what type of fertilizer or nutrients to apply, is to conduct a soil test. You can also simply observe the tree itself. If growth is stunted and you don't see at least 1 foot of growth per year, or what otherwise should be dark green leaves have become light green, this indicates a need for fertilization. If the leaves are light green the tree cannot photosynthesize effectively for the best fruit production. Fertilizer will darken the foliage over time and help to stimulate good fruit production. 

In the absence of a soil test, and if your trees are not growing properly, I recommend using a specialty fruit tree fertilizer at a rate indicated on the package label. Alternatively, you can feed your apple or pear trees as I do with a natural, organic fertilizer at a rate indicated on the bag. If a plant or tree will produce food that I intend on eating, I'm always gonna go organic. The type of fertilizer is up to you. 

NOTE: Although nitrogen is a necessary element for basic plant growth, apple and pear trees, and most other fruit trees, react dramatically if there is too much nitrogen (the first number in fertilizer). The nitrogen redirects energy from fruit production to foliage and shoots. If there's too much nitrogen in the soil fruits might prematurely fall to the ground before they are fully developed. So, avoid the use of high-nitrogen fertilizers. 

When to Fertilize

Newly Planted Trees
When planting an apple or pear tree during the dormant season, when trees have no leaves, do not apply fertilizer. Wait to fertilize until new growth begins to emerge in spring. Container-grown pear trees can be fertilized at planting time when planted during the spring and summer, however avoid fertilization two months prior to the average first-frost date in your area. Late fertilization can stimulate new tender growth that can be damaged by an freeze, compromising the overall health of a tree.

Fertilizing Established Pear Trees
The best time to fertilize your apple or pear trees is when the flower buds are starting to swell in spring. If you miss that time, you can still fertilize anytime through spring. As previously mentioned, to avoid damaging new growth that feeding will stimulate, cease fertilizing two months prior to the average first-frost date in your area. 

Other Helpful Fertilization Tips
  • In general, when applying synthetic fertilizers (non-organic), you should apply these after watering thoroughly. This prevents the fertilizer from burning the tree's delicate roots just under the soil's surface. This is not a concern when applying a non-burning organic fertilizer or aged compost, which can be applied anytime during the season.

  • Once the harvest is complete, stop fertilizing to slow the tree's growth and prevent tender new growth that may be damaged by lower winter temperatures.

Watering Apple and Pear Trees

The frequency and the amount of water an apple or pear tree will need depends to a large extent on the soil, the size of the tree, the time of year, and weather. As a rule of thumb, one inch of water per week from rain or irrigation is adequate. Just keep in mind that soil should be moist but not constantly soggy. Like so many other plants, apple and pear trees do not like constantly wet feet!

Irrigation of young trees is especially important during the first season or two, but be careful not to over water. Mature pear trees are quite drought tolerant but will need sufficient water during the fruiting period to produce a good yield of healthy fruit.

Always keep a sufficient layer of much around your apple and pear trees to help retain moisture and suppress weed growth.

Yellowing and dropping of leaves may indicate drought and the need for supplemental irrigation or need of fertilization.