Monday, February 19, 2018

Heart Wood Rot

Heart wood is the dead wood found in the center of large branches and when combined with the outer sapwood rings, it gives your trees a perfect balance of rigidity and flexibility. Correctly pruning your fruit trees will prevent heart wood rot. Rotten heart wood will not kill your fruit trees, but it will compromise its structural integrity.

If you have ever cut a tree down or split firewood, you have probably seen logs with a dark colored core and lighter, outer rings. Taking a cross section of a trunk or large branch will expose the difference between heart wood and sap wood. 

Heart Wood is the Darker Wood in the Center of Large Branches
The heartwood is dead wood that acts as the structural reinforcement in trees, just like rebar in a concrete footing. The sapwood that wraps around the heart wood is living wood that transports sap filled with water and nutrients to the trunk and canopy. The sapwood is green, flexible wood and will allow a tree to bend and sway. This flexibility in combination with a strong, rigid reinforcement creates a perfect balance, making trees surprisingly strong under stressful situations like wind storms, heavy snow storms, and heavy fruit loads.

Fruit Trees are Strong Under Stress
The following pruning tips will ensure that you prevent heart wood rot in your fruit trees:

  • Start pruning your trees while they are still young
  • Prune your trees every year
  • Don't damage the ridge and collar
  • Make cuts perpendicular to the growth of the branch
  • Cut vertical branches with a slight angle

Start pruning your fruit trees when they are still young. This will ensure that each cut made is done while the branch is still small. If you have a vision for your fruit tree's future form, you can control the shape and direction of growth preventing the need to cut large branches as the tree matures.

Pruning your tree every year will allow you to make smaller cuts more often, also  preventing the need to cut large branches in the future. Find out when is the best time to prune fruit trees by following this link.

The ridges and collars of your fruit trees are extremely important parts of your tree's anatomy. The ridge acts like a check valve that will prevent diseases from entering your tree and makes painting or taring pruning cuts unnecessary. The collar is also extremely important because this part of the tree is what allows a tree to seal off any damage created by a pruning cut. Try to get as close to the collar as possible without damaging it. Leaving stubs out away from the collar will increase the amount of time it takes for the tree to seal off because it will be forced to swell up and around the stub.

There are instances when large branches will need to be removed. When these instances occur it is important to cut them perpendicular to the growth of the branch, minimizing the surface area of the cut. Also, remember to use the three cut method to prevent the weight of the branch to strip the bark off of the trunk.

There is an exception to the rule above. When a branch is growing vertical it is important to cut it with a slight angle. This will increase the surface area of the cut and extend the time it takes to seal, but in this instance cutting the branch perpendicular will cause the swelling tissue that the tree uses to seal the wound to create a small bowl that will capture water and leave it standing on the heart wood and increase the rate of rot. The benefits of the angled cut, although it will leave a larger wound, will outweigh the problems that will occur due to the standing water.

Vertical Cuts Pool Water as They Seal
If rot has been introduced into your tree, it will not kill the tree, but the structural integrity of the tree will be compromised. This may allow other external influences to damage your tree and increase the risk of total tree failure. If rot has been introduced, don't feel the need to cut it down. It is probably still strong, it's just not as strong as it could be with the reinforcement of the heart wood. Also, large mature fruit trees with heart wood rot are established and can still be extremely productive for the rest of their lives.

Don't Cut Down Fruit Tree With Heart Wood Rot
So, even if the structural integrity of your tree is compromised, continue to prune your tree annually. If you are just getting started, make sure your trees are receiving pruning while they are still young. Heart wood rot is one disease that is easily prevented, and impossible to cure.

If you have any questions regarding internal rot or any other fruit tree related topics, email me at We would also like to invite you to join our Back Yard Fruit Growers Facebook Page. This page is a wealth of knowledge from amateurs and professional fruit growers alike.

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