Techniques to save a poisoned tree

Dead tree

Have you sprayed too much insecticide on your tree? Applied too much fertilizer? There may still be a chance to save your plant. Here is how to save a poisoned tree.

Many gardeners have learned the hard way that not all chemical products are good for plants. Perhaps a shrub you were trying to protect from pests is losing all its leaves after being sprayed.

There is a fact to face: not all plants can be saved.

  • Suppliers of chemical pest killers, herbicides and pesticides rarely provide the antidote to the poisons they manufacture.
  • However, try and contact the manufacturer customer service.
  • Sometimes they can share knowledge on how to reverse the effect of their products.

If there’s no known antidote, you’ll have to try to help your plant “ride it out”. You might even save it!

Removing excess product from the plant

If you sprayed the whole tree and it hasn’t rained yet, there might still be lots of product on leaves and bark.

You can wash it off with a hose.

  • Spread tarpaulins, an old watertight table protector, or even large trash bags split open under the tree, plant, or shrub. The goal is to capture the water or channel it to somewhere further off. This is to avoid seepage to the roots.
  • Hose the tree down abundantly to rinse off any product.

Some products are oily or oil-based.

  • To rinse these off, first spray a mix of soap and water.
  • Just a dollop of soap is enough (1 tablespoon for 1 gallon, or 1 teaspoon for a liter).
  • Then, rinse with normal water.

Removing contaminated soil

If most of the product was sprayed to the ground, you can remove most of the soil and replace it with fresh, clean soil.

Professional landscapers and gardeners sometimes perform air spading.

  • This is a technique where compressed air is blasted in the soil to loosen it up and blow it away.
  • Gather contaminated soil and dispose of it in an eco-center or waste disposal center.
  • Be sure to inform the staff of the type of pollutant so that they can guide you to the appropriate bin. It shouldn’t go to the compost or plant material bins!

Locking toxic compounds in Wood Charcoal

To try to cancel out the poison that’s already in the ground, you can grate wood charcoal. Wood charcoal has a tendancy to absorb toxins. It will lock poison up in the ground and prevent it from entering the plant’s root system.

Which charcoal to use to save a poisoned tree

  • This only works with true charcoal, made from wood or plant material. Compacted pellets often used for barbecues won’t be effective here.
  • Use non-treated wood charcoal. Note that some barbecue charcoals have additives that makes them light up easier. Don’t use those as it might add to the poisoning.
  • It’s possible to “activate” your charcoal for an even higher chance of success. However, it’s a long process. It’s often easier to just use the charcoal directly.

How to prepare the charcoal

  • Grate it with a cheese grate or smash it with a mallet or hammer in a pouch (the leg of an old jean works well).
  • Sprinkle it on the ground, about a handful to a square foot (about the surface of a sheet of paper, or 30 by 30 cm).
  • After sprinkling, grab a rake that has strong, short teeth. Work the charcoal into the first inch or two of soil (3-5 cm).
  • Proceed carefully, trying not to damage roots.
  • It should absorb a large part of the toxins.

Over time, as the charcoal itself breaks down, the toxins will be degraded. The impact on the plant won’t be as severe.

Washing out the poison in the ground

Water running from a faucet in the gardenRoots usually only colonize the first 6 to 12 inches of soil (15 to 30 cm). The goal is to wash toxins down to deeper levels. Bacteria and fungus can break them down without affecting the shrubs or trees.

  • Simply water the tree abundantly, soaking the soil down to a foot (30 cm).
  • Repeat after a week, and then again after a week. All in all, three soakings should be enough.
  • After thus rinsing the soil thrice, stop rinsing the soil out. Let it dry (to avoid root rot) and resume watering as normal.

How to treat a poisoned tree

Feed the tree with sugar water

Another technique is effective in helping trees recover from poisoning: sugar water. This provides a boost for the plant and feeds it. It isn’t the same as fertilizing as it doesn’t replenish nutrients, only energy.

  • Use a 1 and ¼ cups of sugar for one gallon of water. This translates to about 10 oz per gallon or 70g per liter.
  • Careful, don’t make it sweeter or the sugar will kill off beneficial bacteria and tiny animal life.
  • Use this mix to water under the tree.
  • For larger trees, make small holes 4-6 inches deep (10-15 cm) in the ground every couple feet (60 to 80 cm). Use a trowel or sharp stick. Then, pour the sugar water in the hole.
  • Repeat once a month during the growing season.

Best is to cover the area where roots are most active. This is usually marked by the drip line on trees that have never been pruned.

  • Tree roots commonly extend from the trunk up to twice as far as the tree canopy is wide.
  • For pruned trees and hedges, cover the ground within a 3 or 4 yard radius (3 or 4 meters).

Avoid high-nitrogen fertilizers

Refrain from providing high-nitrogen fertilizers.

  • High nitrogen levels in the ground will trigger the tree to make lots of leafage.
  • This is because the tree, instead of leafage, needs balanced growth to recover: roots, wood, etc. Nitrogen mostly triggers leaf growth.
  • Since the tree is weakened, the flush of activity on leaves will strain the tree and possibly kill it off.

However, you can nourish the tree with natural weed-based fertilizer

Protect a poisoned tree from stress

The tree or shrub is trying to recover from the poisoning. You’ll have to give it time. Don’t wound the tree any further or subject it to too much stress:

  • Do not prune or trim the tree or shrub for a whole year.
  • Don’t remove any dead wood or branches until the following year. It may seem dead now but might revive after a while.
  • If it’s a low flower-bearing shrub, snip off the buds of at least half the flowers. This preserves the tree’s energy and helps it heal.

Also, protect the tree from other types of stress:

  • Winterize your shrub if there are cold winters in your area.
  • Watch soil moisture by scratching under the surface with your fingers. Avoid overwatering and underwatering.
  • Provide shade for your tree if it’s in a very hot spot. Use a shade net or place a square of cloth on stakes so that the tree or shrub is protected during the hottest hours of the day.

Lastly, don’t try to move or transplant your tree. This would result in transplant shock.

Smart tip about saving poisoned trees

If someone else is poisoning your tree, first find out who. Talk to them peacefully to learn why they’re trying to poison it, and work out what options might work. Sometimes a simple pruning is just what’s needed. Saving your tree will be impossible if someone else hopes for it to die!


Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Dead tree not saved by Oliver Dodd under © CC BY 2.0
Water flushing out tree poison by Amanda under © CC BY 2.0