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forestandfarm

Planting containerized trees in heavy clay

forestandfarm
9 years ago

I've been trying a few methods for planting containerized trees, and I'd like to hear some different opinions on an approach I'm considering.

First, here is the situation. These trees are grown in air pruning containers (rootmaker) with Promix BX so the tap root is pruned. They will be either 1 season old in a 1 gal container or 2 seasons old in a 3 gal container. They will be dormant when planted, probably late winter or early spring in zone 7a. These will be planted in the field where providing supplemental water is difficult if not impossible.

We generally get good spring and fall rain, perhaps too much in some years. Summers can have some significant dry periods.

Species:

Persimmons, Chestnuts, Allegheny Chinquapins, and Pawpaw.

Site Selection:

On slight rises where significant surface runoff is not likely to enter the planting hole.

Approach Under Consideration:

I would auger a hole slightly larger than the container diameter but significantly deeper. Next, I would fill the lower part of the hole with crushed stone followed by a few inches of amended soil (compost, peat, and native clay). I would dunk the root ball in a Watersorb slurry just prior to planting. After inserting the rootball, I would fill around the sides with native clay.

My logic:

Water will infiltrate the Promix much faster than the native soils, so during the abundant spring rain, ponding in the clay could be an issue. The idea of the deep hole would allow water to pond below the root system and not inundate the plant. Hopefully frequent spring rain would keep the Promix moist enough for good growth. The hole diameter being only slightly larger than the rootball would allow the root system to grow laterally into the native clay quickly where it would have access to longer duration moisture because of much slower infiltration. By summer when rains are less frequent and abundant, the ponding area below the plant would hold moisture and over time, the root system would grow down through the amended soil and access this reservoir to the extend needed.

Perhaps I'm all wet here...I'd appreciate any feedback either positive or negative.

Thanks in advance.

Comments (15)

  • drew51 SE MI Z5b/6a
    9 years ago

    Most think it is best not to amend the hole. I have seen one exception. It was for a nut tree that did not like the clay at all. And it was the thickest clay I ever saw. Amending made all the difference. That though was an exception. I see a problem with compost on the bottom. It will eventually decompose and the tree will sink down, not good. Trees should be a high as possible, even root flares showing. You could mound it some to account for settling and decomposition. You might create a bath tub and drown the tree. A pitch fork to all sides would help with drainage. I myself would not put anything in the hole except native soil, a chance the trees or some of them cannot grow in thick clay, then again they have to if amended or not.
    Clay holds water, and dries very slowly. Sand dries out quick. I don't see a problem with lack of water.
    Stones are no longer used at the bottom of pots because it creates a change is soil structure. Water will stop at this change. Often it is advised with raised beds to mix the bottom soil with the soil in the beds so to avoid an abrupt change in soil that will stop water. So again you're creating a bathtub doing this. The stones will not drain away the water, but hold it in place.It is why you put gravel around posts. The change in soil structure prevents water from entering the gravel from the soil, thus keeping the wood dry. In you hole sure water below the stone will not enter, but water above the stones will not pass either.With glazed sides from the digging which will plug the clay up, unless you break that glaze up, it's like the perfect bathtub with the stones holding the water in the glazed bathtub. The trees will surely die.

    Here is the link to another forum site about a tree that did benefit from amending. I think you can amend, it has to be done right and only if really needed. Note his peach tree did fine, and certainly amending that would have been a bad idea. I know little about your tree species, that has to be considered.

    Here is a link that might be useful: Pedro walnut

    This post was edited by Drew51 on Wed, Dec 24, 14 at 3:04

  • fireduck
    9 years ago

    Much of what D says is very true. However, you propose doing some things differently...and I see your logic. In containers, rocks on the bottom does not aide in draining pots. Your situation (I think) is to eliminate saturated rootballs sitting in a flooded clay enclosure. That should help. Also, you stated that the hole will be only slightly larger than the rootball in diameter. This will allow the roots to initially break through the clay, and grab a hold of the ground (also good). The one thing I would add is gypsum in your hole. Many growers believe this helps in breaking down the clay. It can't hurt. Go for it.

  • alan haigh
    9 years ago

    Gypsum only works on sodic clays, from my reading (I've never used gypsum for this reason). Google that and see what you think.

    Not breaking up the soil beyond the rootball is completely the wrong idea. Clay should be worked when moist, not saturated, and broken up so new roots will easily penetrate the clay and will also have adequate oxygen- as much an issue as water. Without enough oxygen water can't be extracted by the roots and roots cannot generate new growth. The more compacted the soil the wider the hole will be.

    Holes dug deeper than the rootball can cause trees to sink as soil settles later. This is why it is no longer recommended, but if you stamp down the soil and plant a little shallow it probably won't be a problem.

    In my nursery I use thin plastic sheeting (think thin garbage bags) about 12-14" down to encourage a shallow root system to simplify digging trees which I install for clients as bare root, baring age trees. I wasn't sure how that would work at first but results have surpassed my hopes as the plastic not only makes the trees easy to dig but also seems to hold water as it is installed with enough concave to hold water.

    You could try that approach several inches lower- hopefully and probably it won't damage the drainage if you don't go beyond about a 2.5' spread. My soil is much coarser than yours and drains very quickly.

    Another option would be to use that soil to plant them in fabric bags where you have water and then transplant them to the permanent location in a couple years.

    I don't believe the watersorb type products have panned out in research and are mostly used just for transporting bare roots from the site they are dug to the site they are planted. I haven't seen any recent literature on the subject, however.

    Obviously eliminating competition of grass and weeds is of optimum importance, either with a couple of Roundup aps, mulching or serious cultivation. This is most crucial through spring.

    Much of what Drew said follows current science which is pretty well laid out in this link.

    The only thing I disagree with in the link is that they suggest mulching over the rootball is not a good idea, but with container trees it may not be, for danger of deflecting rain water.

    Here is a link that might be useful: The science of planting trees

  • steve333_gw
    9 years ago

    I think that whether or not putting rocks and a lighter soil in a hole in your clay soil will have the desired effect depends upon a few things:

    First and foremost is probably the water table in the soil overall. If this is a wet location, prone to surface water or high water table during the year, then rocks at the bottom won't help much. Water is going to fill your tree hole to the soil's water table level, rocks at the bottom or not. If this is the case, planting the trees in a built up mound would be better than any treatment you can give a hole.

    When they might help is if the surrounding soil is fairly dry and you overwater the tree or a flash rain happens. Then the rocks will provide a well drained level the water can collect below the tree roots. Although I am not sure it would be any better than more topsoil mix in that regard. And really this is just compensating for the effect of good well drained soil sitting in a bowl in clay, and only works as long as the overall water table is below the hole, and surround soil is drier than the topsoil. Once the water table gets above the hole or the surrounding soil is saturated then water can no longer exit from the hole, rocks or not.

    It seems to me that you are trying to compensate for the clay soil towards the direction of letting more water in around the roots quickly, with the potential downside that it will flood the roots when water is available in the soil. I don't know your weather patterns, but it seems that has some negatives to it, like flooding and potentially root limiting the trees (trees roots will tend to stay in the good soil rather than explore the surrounding bad stuff).

    You might do better figuring out a means to apply regular water to the trees when needed and plant them in native soil.

    BTW, augers tend to create a glaze on the holes they dig (especially on high clay soils), making root penetration harder. If you can hand dig it would likely be better.


  • alan haigh
    9 years ago

    When I said you should tamp down soil, I meant that if you dig deeper than the rootball you should really stamp the soil down below the depth of the rootball before planting the tree to help prevent the tree from sinking.

    A problem with the root system being in Promix is that it is coarse and clay is fine and capillary action pulls water from coarse to fine so if the clay is dry it will dehydrate the coarse mix very quickly. If you have drought after planting you may need to set up some kind of system to give them drip water from a tank you haul in water to. It wouldn't take to much water this way to keep the plants alive for better days.

  • zendog
    9 years ago

    Hi,
    Sounds like an interesting project. I have a few questions just out of general curiosity, but the probably effect your approach as well. The first is how many trees are you trying to plant and are you doing it pretty much alone? Hand digging would be best, but of course that might not be something you want to contemplate if you're trying to get a hundred trees in the ground quickly.

    The second thing is have you done any drainage tests? If not, I'd suggest you dig a few holes in the area you are considering, either with the auger or by hand and fill them with water and see how long it takes to drain. If your soil is already very dry, you may have to add water several times to build up saturation levels around the hole. Depending on the clay it may not drain as slowly as you imagine it might... or it might take days. Either way, that could impact your planning significantly.

  • grow_life
    9 years ago

    Lots of good advice. I'm an arborist who plants tons of trees in heavy, sometimes straight blue, clay that has had vehicles driving over it. Awesome digging, I can tell you. Dig no deeper than proper planting depth, dig sloping sides twice as wide as the pot, rough up the sides of the hole, backfill with native soil, and above all, mulch mulch mulch. A good thick doughnut of wood chips around the whole thing as wide as you can go, keeping it away from the trunk. Mulch repeatedly over many seasons if you can. Unless it's a boggy area even in dry weather, don't worry about drowning them. Good luck!

  • copingwithclay
    9 years ago

    I share your zeal to get plants in the ground sooner rather than later. Unless. Unless waiting another couple years (WHAT?!) for the root system to develop much more will be a prudent step that is worth the wait. Transpotting them into bigger pots/enclosures and providing consistent moisture/fertilizing/bright sunlight can help maximize the growth and thus speed up the wait........If young plants with a small root system have to attempt surviving during dry times when it is too difficult for you to keep their juvenile root systems fully hydrated. your plants will never forgive you. They can die. BIGGER plants with BIGGER root systems may be able to collect moisture over a larger area.....and thus making them more resilient......Bad times will come along. 'Sooner' is more threatening to small root systems.... that you are unable to conveniently keep in good care.

  • forestandfarm
    Original Author
    9 years ago

    Thanks for all the input. First, some answers to some of your questions:

    I'll be planting these trees by the hundreds. They will be in a wildlife setting several hours from my home. Supplemental water is not an option. I may have some help, but for the most part, I'll be on my own.

    Some of the responses seem to capture the situation with the containerized root pruned trees. With coarse promix inserted into heavy clay, water will infiltrate through the mix and it will dry out as some of you suggest. So, if I dig a wide hole like folks do in other situations, I'm afraid that it will take a long time before the roots make it into the native soils where the moisture will be retained. My hope is keeping the diameter of the hole close to the container size is that by summer when soils dry out, root tips will be in the native soils.

    As for using an auger to dig the holes, it is pretty much the only option. I'm familiar with the glazing effect in clay. I solve that by simply taking a hand rake and roughing up the sides of the holes after digging.

    Another of you hit the nail on the head with my purpose for the rocks and amended soil below the plant. The idea was to make sure the rootball does not get saturated.

    Drainage in my clay is slow. It is one of those properties where you need to work to find a spot that perks for a drain field.

    Most of these seedling I'm growing from seed in my basement. I have some that I've started last year that will be my guinea pigs this spring. The big push won't come until the following spring so I have time to learn.

    I really appreciate all the responses and they are all making me think about things in different ways.

  • steve333_gw
    9 years ago

    F&F, I think you missed the part with the wide hole suggestion that has you using native soil to refill. If you did use native soil, you would eliminate your concern with the long travel for the roots to native, hydrated soil. They would be in that from the start.

    It will obviously depend on your choice of fill material, but in your quest to keep the root ball from saturating, you may be drying them out too much. Sounds like they will live or die by the local rainfall. If you accept that, then they may do the best they can in all native backfill. Other approaches can optimize for one extreme of condition or the other, but not the overall average

  • alan haigh
    9 years ago

    Actually, it sounds as though you may be wasting your time. You don't seem to have the resources that will likely be required, including weed control.

    If the trees cannot establish by simply being placed in an augered hole you will find out soon enough, but don't think a smaller hole makes it easier for new roots to quickly establish in your clay soil- the opposite is true. Putting rocks on the bottom of the hole won't matter either, IMO. Just use as wide an auger as your tractor can push through that clay and leave it at that.

    If you can afford biodegradable weed barrier squares it might increase the odds. I doubt the trees will survive the weed competition otherwise unless you find the time to apply Roundup at least the first season.

  • drew51 SE MI Z5b/6a
    9 years ago

    The rocks will hold water not drain it. As I said you're creating a bath tub. The glazing will not be solved by a shallow roughing of the edge. If you want to create an even worse bathtub, amend the soil. These trees are going to drown, no doubt. No offense but these are major rookie mistakes. If you had any experience with planting out trees, you would know this. I have made plenty of bathtubs myself to know it is exactly what's going to happen. Use only native soil. That's hitting the nail on the head. If the plants survive the first year the good news is the rocks and amendments will be assimilated into the native soil, and the glazing will breakdown by then.
    No matter what you do somewhat of a bathtub effect will happen in clay soil, my best solution to that is mounding, and new plants have few roots deep in the tub.

    This post was edited by Drew51 on Thu, Dec 25, 14 at 9:41

  • forestandfarm
    Original Author
    9 years ago

    Good inputs! My experience planting trees is limited. So far, I only have a couple hundred chestnut trees in the ground. I've tried two methods so far. The first method was to auger deep holes and amend below the tree with no rocks as well as around the rootball. The auger size gave me a hole about 9"-10" in diameter and about 3' deep. These trees were started in December from nuts under lights indoors. They were a foot to 18" tall when planted the following April. I used no weed control but they were mostly planted in clover fields and the clover chokes out many of the weeds. Some of the containers were about 5" in diameter and others were closer to 9". I did try to protect most of them from browsing with tree tubes. Some I used short 18" solid tubes on the bottom with 3' mesh tubes on the top On others I used 3' solid tubes with 3' mesh tubes on the top. None had supplemental water.

    These trees now have 2 growing seasons under their belts. I'd estimate I had about 15% losses so far. These trees now range from about 4' to 7' tall.

    While I did not keep track tree by tree, my sense is that the ones in the wider containers (less amended soil between the root ball and native soils) grew better during the first summer.

    The second method I tried was to plant them from small cells (about 2 1/2 x 2 1/2 x 3 deep). With these I used a planting bar in a non-traditional way. I jammed the blade into the ground and rotated to carve out a hole the size of the cell. Again, I used no weed control but did use small tubes on half and left the other half unprotected. These were 9"-12" when planted.

    These trees have only been in the ground one growing season, so I won't really know survival rates until spring. My general sense is that while the planting effort is much lower, my survival rates will also be lower.

    Because I'm growing these trees from seed, the cost per tree is low and I am willing to accept some losses.

    You folks are absolutely correct about the bathtub effect and that is what I was going for. My intent was to create that bathtub far enough below the rootball that I don't drown the tree. I'm sure that in some cases I failed to get it right. I was hoping that adding the rocks would create more voids to hold water below the root ball.

    For those who suggested weed barriers and allowing trees to mature more before planting, I'm doing that as well. In those cases, I have a lot more invested in each tree and do plan will be planting these in more strategic locations with more care. In addition, I'll probably be retrofitting my best trees with gly and a weed barrier. I wanted to let them get a couple growing seasons under their belts first. Since I can't afford to do this will all, I figured I'd do it with the strongest.

    Thanks again for all the insights. Keep them coming. I'm learning as I go.

    Merry Christmas!!!

  • skyjs
    9 years ago

    Only amend your soil to make it half way between the crappy clay you've got and the best soil for that tree. I use gravel mixed in with my heavy clay in the lower part of the hole, and it helps a lot with drainage, but like others said, it has to be mixed in, not a separate layer. Like others have said, if you don't amend heavy clay in a rainy climate and leave the tree at the same level, the trees will likely drown, catch diseases and die. I also use old wood branches mixed in, like 1 inch diameter by 4 to 8 inches, deep in the hole as these trees need fungal based soils. The wood retains some moisture in dry parts of year as it rots but also drains. The soil must be mounded up over the hole, so it's above the other soil line, because they will sink somewhat. I put compost or ramial wood chips on top only. Research by Linda Chalker Scott of Washington proves this method. I have planted and later dug out many trees this way and they were all very healthy.
    John S
    PDX OR

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