Percolation problems? Dam it.

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So you’ve been diligently watering and fertilizing all season, but the water now just seems to run off the edge of the pot and into oblivion, leaving your root ball high and dry. You check the soil and it’s still dry under the surface and the water is not getting where it needs to go. Even though we are transitioning into fall, the trees are still consuming a lot of water. One of the main causes of this loss of percolation is the build up of unused fertilizer on the surface of the soil, along with weeds, old leaves, dead moss, etc… The soil is too compacted for the water to penetrate. There are a few ways to address the situation. 

First of all, if you have just repotted in the last year or two, the soil underneath is likely fresh and still granular. Just scrape off the crust, down to the good soil and replace with fresh soil if needed, and then top dress with shredded moss (half dried, clean sphagnum and half fresh green) to start re-growing a nice healthy carpet on the soil surface. That carpet of moss does many things and one of the most important is grabbing that fresh water from your hose and directing it down into the root zone. Be sure to not go too deep in your cleaning efforts. It may be best to wait until you can repot in the spring to tackle the roots properly. 


Rope dam applied to sloped and compacted root ball. 

If we have hard, compacted soil from a tree that has not been repotted in four or five or more years, we need a different strategy. It is likely that the loss of percolation is impacting the health of the tree. So we need to get that water in there to build up the health of the tree BEFORE a Spring repot we can address the roots and compacted soil. So how do we do that? Something that I am trying this year is to build a small dam around the edge of the pot with a length of rope. I just used some half-inch sisal rope I had on hand. I cut it to length and fastened it to the soil with staples made from bonsai wire. I really like the natural fibers best. Cotton or hemp might also work well.  

In my case, I was dealing with a very old mountain hemlock with steep sides to the root ball. The first time I repotted it I had to use a reciprocating saw to cut a slab of roots from the bottom just to get it back into the pot. It had been many years since the previous owner had done anything. In my last repotting, I shoehorned the tree into a new pot, so I did not have a safe opportunity to really tackle the issue properly. And so, my current dilemma. In this case, I made two rows of rope dam to slow down the water so that it would percolate into the root ball and the technique has worked marvelously. It also keeps the fertilizer from washing away. 

Another method, which I have not yet, tried myself, is to make a wall all the way around the outside of the rim of the pot with duct tape, or something similar. All we are trying to do is to redirect the water into the pot. Of course, this method is more drastic, and there will be some clean up later, but we do what is needed for the health of the tree. Give these methods a try. 

That’s the reason we try to leave a quarter to half-inch drop between the rim of the pot and soil level when we repot. Actually, since my first draft of this article, Ryan Neil has released a new video on Mirai Live about this very technique. He goes into great detail about the symptoms and signs of a flagging tree and how to address the situation. 

I wanted to fit in another seasonal subject here. Actually, it’s several things that are very interrelated, so pay attention. As you will see in my Hard Won Truths for this month, this is the best and most important time of year to fertilize. But why? The tree is now doing several things. It has shifted from foliar growth to vascular growth. That means that it is storing up energy for winter and beginning to build its defenses against the cold, packing nutrients into the cells. It’s also creating new cells and building vascular tissue, as well as next years buds. We want to supply as much nutrition as we can to the tree to help it build. All of the foliage has hardened off by now, so we don’t have to worry about long needles, large leaves, or long internodes. 


Unfortunately, this means that since the tree is putting on vascular tissue (growth rings) any wire we have on a tree may be cutting in. If it is starting to cut in now, it is really going to be dug in by the end of the season. I think that I may have more experience than anyone around at dealing with deeply cutting wire and ugly scars. Wire has stayed on many of my trees way too long and at times I have been forced to just cut them off. Branches fool you because they don’t all cut in the same amount, or in the same areas. The branch tips rarely cut in. 

Look for the areas where you made a sharp bend, or where you have had a lot of foliage growth, or where a branch forks from the trunk or another branch. Those are the areas where the tree adds tissue the quickest. Elongating species like fir, hemlock, and spruce are perhaps the worst since they have most of their strength in that vascular tissue and tend to really bulk up this time of year. 

But all of this also means that this is the best time to wire. You can get that branch setting mass in just a few months, and any minor damage done by bending or applying wire can be repaired by the tree before winter. So if you take wire off, put it right back on, if needed, to maximize your efforts. If you remove the wire on conifers, before it starts cutting in a little, then you really haven’t gained much. Worse, if you don’t rewire it, the tree will add tissue in the position that you just tried to correct. 

So the trick is to be able to work your tree so that you only take off and replace what is needed and save yourself some work. If it has been several years, then it has likely out grown the length, if not also the strength, of the wire and it will have to be redone. So that is how my fall work is shaping up - lots of unwiring and rewiring. But, I am making more headway than in the past.