Regional Gardening Reports :: National Gardening Association

In the Garden:
Southwestern Deserts
June, 2011
Regional Report

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No trunk flare is visible, meaning this tree was planted too deeply.

Tree Planting Depth

Out and about looking at trees with a local horticulture expert recently, we were dismayed to see newly transplanted, 24-inch box trees in a public planting had been planted too deeply, which can ultimately kill the tree. What a waste to spend significant amounts of time and money on mature trees only to have them improperly planted! Knowing where to look for trunk flare can help you avoid this transplanting mistake.

Find the Flare
Trunk flare (some folks may call it root flare) is the area at the base of the trunk where roots start spreading. Trunk flare is a little wider than the rest of the trunk. It signals a physiological change from root tissue that absorbs water and nutrients from surrounding soil to trunk tissue that transports water and nutrients up through the plant where leaves can do their job of photosynthesis.

Trunk flare should be partially visible after you have transplanted your tree. Your newly planted tree shouldn't look like a straight telephone pole! If the flare is not visible, the roots are likely too far below ground to obtain essential oxygen. Roots without oxygen die. Trees with dead roots die! Also, the regular trunk tissue that is buried too deeply is susceptible to rot.

Transplant At or Just Above Grade
A general guideline to follow when transplanting from containers is that the top of the root ball should be at or slightly above the soil surface. In clay soil, it must be slightly above the soil surface because clay is prone to compaction and the weight of the tree will cause it to sink below grade. This guideline works fine if your tree was properly grown as it was potted up in larger containers, with the flare above ground. If not, you may need to remove some of the soil from around the top of the root ball before transplanting. (Better yet, don't buy trees if their trunk flare isn't visible.)

If you are planting bare root trees, look for trunk flare and position it properly in the hole. Finally, it is better to plant an inch or two high above the base of the trunk flare, rather than to plant it too low, as some settling is likely to occur.

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