Fertilizing Fruit Trees

Fruit trees are a perennial, woody addition to any landscape, homestead or commercial operation.  Selection of varietals depends greatly on the intended use for the tree(s).  Ranging from landscape designs of flowering hedge rows to the intense production in commercial orchards, fruit trees have always been a part of America’s history.  Even though the term fruit tree is a very broad category, fertilizing them does not have to be. 

The first step to utilizing fruit trees is to select varietals that are suitable for that specific environment.  This is often referred to as climate zones, but this goes much further than a number on a map.  The environment also includes soil types and fertility, location, and drainage.  After a suitable location has been established, a representative soil sample(s) must be analyzed.  This is the point in a tree’s life that the soil environment can be both economically and efficiently amended for the best start.      

Soil pH is the priority when considering any soil amendment.  The pH directly impacts the availability of nutrients to plants.  Certain plants thrive in different soil acidities.  Blueberries, for example, do well in acidic soils.  A pH of 4.0-5.5 makes nutrients like iron more accessible.  Without the acidity of the soil nutrients are left unavailable to the plant.  Fruit trees grow and thrive in a soil pH of 6.0-7.0.  One careful note when analyzing soil acidity is that some nutrients levels become toxic at different pH levels.

Often, a grower will “amend” the soil in the newly dug rootzone.  The hole is generally dug wide and deep enough that the roots do not touch the edges when held in place.  Some will recommend mixing sand, compost, peat, coir, or different soil in the new tree bed.  This is a quick fix for certain problems such as drainage, nutrient requirements, and/or water retention but in some cases not the best option for long-term health.  This can lead to trees needing to be staked for proper growth direction from the root bed being too loose or soil surface being too low.  Some additions can lower the pH too much, and breakdown over time.  Creating a micro-climate for the root bed can lead to roots wrapping around the edges or not penetrating the outside walls into native soils.  The best option is to choose the right place to plant and add the native soil back to the hole.

If a soil test shows deficiencies of certain nutrients, it is important to know how much and of what specific fertilizer to address the issue(s).  There are fertilizers that are immediately available for plant uptake and others, like elemental sulfur, that are not. Some deficiencies could be from inconsistent watering/weather.  After two years from planting young fruit trees, regular watering should be less and less depending on climate.  This allows the roots to develop and not become too shallow and grow vertically rather than horizontally.  This is especially important in high wind environments where a deep root system provides stability. 

Early spring is the best time to fertilize fruit trees.  This allows the application to leach down into the rootzone from the ample, seasonal moisture.  Depending on the fertilizer used, it will give it time to convert to available forms.  Nutrients need to be in an inorganic formulation for uptake.  If a composted manure is applied to each tree, or blanket spread on the landscape, it will need time to mineralize.  The same process allows soil organic matter to release nutrients such as nitrogen and sulfur through mineralization.

Applications made in late spring, summer and/or fall may cause rapid growth too late in the season.  These later fertilizer applications can inhibit fruiting while producing vegetative growth and possible winter injury.  All living plants need nutrients, but production crops where the fruit is harvested requires knowing what is already available and what needs to be supplemented for that crop.