Question: I have a mature (10 yrs. old) globe willow. The leaves are turning brown starting at tips then whole leaf turns brown and drops. The tree had been planted in area that had been covered with black heavy plastic then covered with rocks, with only 4 ft. area at base of tree left to water. I've added iron to the soil and watered in but hasn't helped. It has no disease or pests present. This is the first year this has occurred and I'm afraid the tree is dying. What, if anything, can I do to help it?
Rip out that black plastic! It used to be recommended, but now it's realized that it prevents deep water penetration and forces roots to grow along the top inches of soil. Those brown tips and then brown leaves, sound like salt burn. The salts in our water and soils accumulate where the water stops penetrating. So if the water isn't going past the roots, the salt will build up and kill them over time.
Also, as a tree grows, its new roots tips, where nutrients are being absorbed, spread out laterally. If you are watering only within a four-foot area at the base of the tree, it's not really being watered effectively. Get rid of the plastic, the rocks can stay if you want because water will filter through them, and expand your watering zone out PAST the tree's canopy. As the tree
grows, continue expanding that water zone. If you have an irrigation system, you need to move the emitters out. If you use a hose, just drag it out further. In any case, water slowly and deeply to ensure water penetration and to leach salts below the root zone. Don't fertilize until next spring.
Also, iron deficiency typically shows up at yellow leaves with green veins. I hope this info helps your willow. Good luck!
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