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What Does It Mean if a Tree Bleeds Sap?

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Question: What Does It Mean if a Tree Bleeds Sap?
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There are some trees that you should wait to prune until later in the spring because they tend to bleed sap. What does this mean? Should you be concerned?

Much like the veins in our body, the tree's vascular system transports sap, a sugary liquid filled with water and nutrients, throughout the tree via the phloem and xylem. If a cut is made in the trunk, the sap may start oozing out.

The amount of sap in the tree varies based on the time of year. In some kinds of trees, the sap levels are especially high in early spring. If you make pruning cuts at that time, the tree may bleed sap. This isn't usually too much of a problem, but it's best to avoid it so you can avoid problems like gummosis and tree decline.

The best way to control bleeding sap is to prune at the right time for your tree type. If your pruning cut does bleed, just leave it alone. Don't paint or cover the wound. The one possible exception is if you have an elm or oak tree that is bleeding. These are highly susceptible to Dutch elm disease and oak wilt respectively, so painting over the would will help keep the disease out, according to the US Forest Service.

Some Trees That Tend to Bleed Sap:

  • Beeches (Fagus)
  • Birches (Betula)
  • Elms (Ulmus)
  • Grapes (Vitis)
  • Lindens (Tilia)
  • Maples (Acer)
  • Mulberries (Morus)
  • Poplars (Populus)
  • Walnuts (Juglans)

Bleeding sap isn't always a negative phenomenon, however. We are able to collect maple sap each year from maple trees by tapping the trunk. It takes over 40 gallons of sap to make one gallon of maple syrup. Some people also like to make beverages from birch tree sap.

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