There is a plethora of commonly held beliefs about tree roots. For example, many people have been taught that a tree’s root system closely resembles its trunk and branches. However, the truth is much more nuanced.
There is no simple, one-size-fits-all answer to the question of fruit tree root depth because numerous factors influence how deep roots will grow. That said, there are a few key guidelines worth noting:
Fruit trees’ roots are very shallow, often only reaching depths of three feet below the ground. In fact, they will only grow as deep as they need to grow to find sufficient water. The breadth of their root system is much more important and extensive.
It may also surprise you to learn that all fruit trees, including apples, stone fruits, and citrus, have the same root system depth and breadth when they are planted in the right kind of soil and cared for properly.
Root System Depth
One common misconception about tree roots is that they are as deep as the tree is tall. The truth is that very few of a tree’s roots extend deeper than 18 inches below the ground (source).
In fact, trees can grow in as little as 18 inches of soil; however, fruit trees planted in soil that shallow will be stunted (source).
Trees have two types of roots, taproots and fibrous roots. Taproots grow vertically and can become quite large and trunk-like. Not only do taproots stabilize the above-ground growth of the tree, they are also critical to a tree’s search for water.
Non-fruiting trees usually only have one or two taproots, reaching depths of 30 feet or more. However, many fruit trees do not develop deep taproots at all (source).
There are exceptions to this based on the type of fruit tree, rootstock, the quality of soil, and how high or low the water table is in your area. In general, though, fruit trees don’t need to grow very deep taproots when they are planted in good soil with sufficient water and nutrients.
In essence, the drier the soil, the deeper the roots will need to grow to hunt for water.
Root System Breadth
Fibrous roots, on the other hand, make up the majority of a tree’s root system. These extend outward horizontally from the base of the tree and mainly develop within the top 12 inches of soil where nutrients are more abundant (source).
Fibrous roots can’t grow and thrive in oxygen-deficient soils. This is primarily why they grow so close to the surface. The deeper the soil, the less likely roots will find the oxygen they need.
Fruit-bearing trees from the rose family, such as apples, apricots, cherries, peaches, pears, and plums, are especially dependent on the oxygen they receive from their fibrous roots (source). This means that when they are healthy and thriving, these types of trees’ roots are more likely to have significant breadth rather than significant depth.
Don’t be fooled by the term “fibrous.” While some fibrous roots are small, less than an inch in diameter, the tree’s main fibrous roots can be anywhere from three to 15 feet in diameter near the trunk (source).
When a tree is healthy, its fibrous root system is likely to be huge! In fact, a tree’s root system can reach a circumference four to seven times the circumference of its branches (source).
Factors Affecting Root Depth
The factors that have the most influence on root depth are:
- Soil conditions
- Water availability
- Pruning practices
- Rootstock selection
Ideally, for your tree to be healthy and produce fruit, your soil should meet the following conditions:
- A pH level between 6.0 and 7.0 (slightly acidic)
- Loam or sandy loam consistency
- Good drainage
Under these conditions, most of your fruit tree’s roots will develop in the top three feet of soil.
You can also contact your local extension agent or soil expert about having your soil tested. Alternatively, you can do this yourself by purchasing a soil test online (link to Amazon). This will tell you the pH level of your soil as well as which nutrients you may need to supplement.
Furthermore, your fruit tree’s root system will need plenty of space to grow outward without competing with other fruit trees for nutrients and water. You can calculate the amount of space you’ll need by the tree’s full height potential. If you expect your fruit tree to be 25 feet tall, don’t plant another tree within 25 feet of it (source).
Loam or sandy loam are ideal for trees because they retain moisture, but not excessively, and allow enough oxygen to still flow freely in the top few feet of soil. Unfortunately, not every grower is blessed with perfect soil.
Tree roots will often thrive in sandy soils because of the availability of oxygen in sand. The downside of sandy soils, however, is that they drain quickly, sometimes too quickly to meet the tree’s needs. If you have sandy soil, plan to irrigate and fertilize your tree regularly.
If your home is newly built, your yard is likely composed of “made” soil. “Made” soil is a term that refers to soil in landscapes that have recently been under construction. Because of grading, compaction by heavy machinery, and mixing of soils from a variety of locations, tree roots will struggle to take hold in “made” soil (source).
The primary problem with “made” soil is the loss of oxygen from compaction, which may require vertical mulching, engineered soil, and help from a tree expert to fix.
Clay is extremely problematic for root systems because it is heavy and often water-logged. Oxygen doesn’t flow freely in clay soil, so roots cannot grow freely, either. Before you plant in clay, you will need to do significant soil preparation.
Salty soils are also difficult environments for tree planting. Salts can burn tree roots, but in addition to that, salty soils usually coexist with high water tables, which can lead to rot in the roots that do exist. Fruit trees are simply unlikely to thrive in salty soils without a great deal of mitigation (source).
If the soil in your area is poor, consider planting your fruit tree in a pot (see below).
Fruit trees require tremendous amounts of water to produce fruit. In fact, a single well-established peach tree can use approximately 45 gallons of water each day in the height of summer (source).
The problem, of course, is that their roots won’t succeed in water-logged soil.
So, if you live in an area with good rainfall or a high water table, you will probably not need to irrigate your fruit trees. In fact, irrigating trees in a wet climate is simply not a good idea. See this article on the signs of overwatered plants.
If you don’t know how high your water table is, consult the U.S. Geological Survey’s National Ground-Water Monitoring Network.
During drought periods and in dry areas, fruit trees will need to be watered, but only occasionally. Water young trees every 10-14 days and mature trees every three to four weeks. This occasional watering will prod your tree’s roots to grow deeper toward the water table.
It may seem counterintuitive, but pruning your tree’s branches will also affect the growth of its roots.
It is common knowledge that roots and branches transmit water and nutrients to each other. However, they also transmit growth hormones as well (source).
When trees are pruned to encourage new branches to grow, growth hormones are stimulated in both the branches and the root system. Essentially, as new branches grow, new roots will grow as well.
It is critical to note that this will only be the case when trees are pruned at the appropriate time and to an appropriate degree.
Over-pruning can lead to a steep decline in root growth and function. This leads to further problems for the tree’s health since it won’t be able to take in as much water and nutrients.
When you prune a young, recently established tree, avoid pruning more than 50% of its foliage at one time. Middle-aged trees should not lose more than 25% of foliage in one pruning session, and mature trees not more than 10% of foliage (source).
Don’t be afraid to prune your trees, since pruning does promote healthy branch and root development. Just take care to prune responsibly in order to avoid triggering an irrevocable stress response in your tree.
Rootstocks comprise the lower portion of the tree, including its root system. The upper portion of the tree, the scion, is grafted onto the rootstock. Stone fruits, pears, and apples all have different rootstocks growers can choose from (source).
Rootstocks control quite a few growing variables including height, yield, and lifespan. Proper rootstock selection is also a good way to control the size of your fruit tree’s root system. This is especially advantageous for growers with limited space or less-than-ideal soil conditions.
If space is a concern for you, consider dwarfing, semi-dwarfing, or extremely dwarfing rootstocks. These varieties’ root systems generally only grow to areas of approximately three to six square feet, compared to the 33 to 39 square-foot area of full-sized fruit trees (source).
Dwarfing rootstocks are available for apples, pears, and stone fruits, including some almonds.
Nectarines, peaches, and tart cherry trees are self-fruitful; they do not need another tree to produce fruit. They can also be grafted onto dwarfing rootstocks. This makes them great candidates for growers who have limited space.
Rootstocks can also affect a fruit tree’s tolerance of drought and soil conditions. Some, like the Citation rootstock for stone fruits, have even been adapted to tolerate soils that drain poorly.
Novice growers should consult their local extension agents or horticulturalists for advice on which rootstocks are likely to succeed in your area.
Apples and Pears
When planting pome fruits (apples and pears) that have been grafted onto a rootstock, the rule of thumb is to keep the scion-rootstock union four to six inches above the surface (source). Allow for some settling to occur after planting.
You can plant stone fruit trees a little deeper than apple trees; however, if you plant them too deep, they won’t receive enough oxygen. Aim for the highest lateral roots to be about two inches deep. This will put the scion-rootstock union approximately two inches above the surface (source).
Again, expect the tree to settle a bit after planting.
When planting bare-root citrus trees, measure the depth of the root ball, then dig your hole to be one inch shallower than the root ball (source). Once you’ve refilled the hole, add about half an inch of soil to the root crown to prevent it from drying out.
Diameter vs. Depth
When planting any kind of bare-root fruit tree, as opposed to planting from seed, the planting depth is less important than the hole’s diameter. When planted, the roots should not be bent or laid over each other. There should be ample room to settle them in a natural position (source).
Furthermore, if you dig a hole approximately twice as wide as the new tree’s root system, you will help your tree become established. Since you have done the work of breaking up the soil, the roots will find it easier to grow outward (source).
Growing Fruit Trees in Pots
If you want to plant a fruit tree, but the soil in your area presents too many difficulties, consider growing your tree in a pot. There are several advantages to this approach:
- There is a wide variety of fruit trees that can thrive and bear fruit when planted in a pot, including dwarf cherries, key limes, Meyer lemons, and even avocados (source).
- You have more control over the quality of the soil. Potting mixes that are available at garden centers and nurseries will generally work, but you can also make your own potting mix out of sand, peat, and perlite (source).
- You would have greater control over irrigation. When a tree is in a pot, it is much easier to judge whether it is receiving enough or too much water (source).
- Fruit trees grown in pots often don’t require much, if any, fertilization. Depending on which fruit you plant and the potting mix you use, your tree roots will have all the nutrients they need without supplements (source).
- Container planting also allows you to grow fruit that would not normally survive outside of its native climate. Since containers are portable, you can move your tree to shelter in the winter. Some fruit trees can be grown completely indoors, as long as they still have adequate sunlight.
Of course, trees grown in pots can’t stretch their root systems as extensively as trees grown in high-quality earth. This makes rootstock and variety selection extremely important. Your local Extension agent or horticulturalist can help you select an appropriate rootstock and scion for the fruit you wish to grow.
The vast majority of a fruit tree’s root system is shallow, horizontal growth. With some exceptions, they will only grow deep taproots if water isn’t available closer to the surface. Fruit tree roots prefer to stay in the top three feet of soil where they can absorb oxygen and other minerals easily.
If the soil in your area is “made” soil, clay, or salty, don’t be discouraged from planting fruit trees! Planting fruit trees in pots gives you control over many important variables and allows you to enjoy your favorite fruits even outside of their native climates.