The use of quicklime (CaO) to remove lichen and moss from trees is an almost forgotten art in the 21st century.
There are a number of reasons for this, such as easier and hence more frequent trimming of trees using machinery. This reduces the density of the tree canopy, letting air circulate better, which reduces the buildup of moss and lichen.
Another reason is that trees on commercial farms simply don't grow as old as in previous times. Once production declines, cutting old trees and planting new ones is more profitable than getting several more decades of life out of a fruit or nut tree.
And finally, there is the high pressure water cleaner you know from car washes or building contractors. Although not as efficient as the quicklime method and tricky because of the potential of serious damage to recent growth, it is fast and "good enough".
And don't underestimate the "crazy factor". If passers by or neighbors see you on a ladder painting the whole tree, including the smallest branches white - which is what the quicklime method looks like - you will get asked what the heck you are doing.
Chemistry note
It's Calcium, not only harmless but beneficial.
Types of trees treated
I have used this method on a wide range of trees, such as walnuts, apples, cherries, plums and elderberries and on many shrubs and not had any problems.
Here is how to restore a tree using quicklime and water
Find a building supplier or a farming co-op and buy quicklime. Make sure to get the right kind of lime, don't just ask for "lime". Most kinds are not usable at all or not as efficient.
The lime you want is the stuff that bubbles and gets hot, very hot, when you add water to it.
Lime is sold in bags, mostly 25 or 50 pounds. Ideally, you'd get the great 100% CaO stuff, totally white. These days, it may be hard to find, as most store sell lime with 75 to 85% CaO.
This makes for safer transport and handling because the inert "other" minerals reduce the volatility of the product.
But you do need protective goggles for your eyes and leather gardening gloves either way. An old pair of jeans - no large tears - and an old wool or cotton shirt as well as old leather shoes or boots complete the protective gear you must wear.
Tools needed: two sturdy buckets, one of which should be a 2 to 2.5 gallon (10 liter) bucket, which is a good size to schlepp up and down the ladder. The second bucket can be larger or smaller, it will contain only water.
Get a couple of paint brushes, one to two or so inches wide, for more efficient application of the lime.
A trowel would be perfect for getting lime out of the bag, a stick will do best for mixing.
Choosing the right brushes
It is perfectly fine to wonder about this paragraph header or to imagine a couple of small cartoon style question marks.
You are not embarking on a watercolor or a fine art work, so why does the choice of brushes matter?
Because of the heat of the lime & water mixture.
The cheap set of 5 or 10 brushes offered on sale at the hardware store are just fine, but you will go through several brushes as the heat eats away at them. Some old pig hair brush turned out to be the longest lasting one for me, but it really doesn't matter, and new ones are too expensive for tree painting.
Prepare the lime & water mixture
Start out small and cautious. Got your old clothes as well as the goggles on? Gloves, too?
Find a dry place outside - you don't want the bottom of the bag get moist on grass or so.
Fill the water bucket, open the bag of lime. Transfer a pound or two of lime into the empty bucket, then pour in a pint or two (up to a liter) of water. If you have the all white, pure lime, it will throw bubbles the moment the water hits the lime. Mix with the stick. As the lime reacts with the water, the bucket will get hot, and the mixture with thicken. The thickness of the mixture once the reaction ends (no more bubbles, no increase in heat) determines how easy the paint job is.
My preferred thickness is somewhat like a thick Thanksgiving gravy. You want a good, thick coat on the branches - as opposed to painting, say, a wall or a piece of wood, for which you want thin coats.
The "safety lime" takes its sweet time to fully react with the water and does so much less violently. This product can easily take 10 or 15 minutes to dissolve, and you will need to loosen it with the trowel several times in the process and also add water more often. It will work, just be patient and feel the heat.
Start painting, be generous
Start from the ground on a low branch or even the trunk to get a feeling for the lime mix. Moss or lichen will try to repel it, so you go over those patches a couple of times in a back and forth motion, ensuring to cover them nicely.
Don't try to get only the larger patches of moss or lichen, paint the whole branch, also the underside.
Once you are comfortable with the feel of the mixture and the required motions, get that ladder and enjoy.
Passers by and neighbors
You will get comments and questions. Professional landscapers may be either the nicest or the worst audience, and there are only two things you can do about it:
Remain friendly, explain this is a traditional technique.
Don't tell them you read it on a blog - unless you have seen the results of your work and know we gave you great advice.
The results
The mixture will suck water out of moss and lichen while not harming the bark of the tree at all. It also changes the pH, the "acidity", of the branch to the detriment of moss and lichen, and it kills tiny pests that hide unseen in moss and lichen.
Once the coat as dried out, peel away a small piece from a lichen or moss patch. The killed off moss or lichen will be blackish, hard and crumbly.
Over the subsequent months, the coat will come off all by itself, taking the dead lichen and moss with it, just leave the tree alone. Assuming you did the work in fall, you should have a fairly clear bark the next spring.
Emergency restoration during the summer
It can be done. It is just very messy, and you won't get all of the offending parasites at that time.
However, if a tree has been neglected for a decade or longer and the parasites are causing bark to fall of in big chunks, an emergency paint job may be the only chance of saving the tree.
It is pretty impressive to see how quickly treated branches recover, especially if you have some branches that cannot be done at the same time. The difference in ark health, foliage and new growth is striking.
One more thing
If you decide to build a machine and become famous as a tree restorer, be so kind to drop us an email.
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