Effect of container depth on chestnut seedling development

For the past two years, our farm has been studying the role nursery container depth plays in the initial development of chestnut seedlings as a taprooting tree species through a SARE grant (Project FNE20-947).

We created five experimental container groups: 6", 9", 12", 15", and 24" with 128 seeds per group that we raised in a nursery in 2020. The idea with the 24" group was to simulate conditions where taproot growth was uninhibited. In the second year, we transplanted ~70 of the healthiest from each group into the field. Aerial height, caliper, and root length were measured.

The results were interesting. We found that a shallower container produced significantly more aerial growth in the nursery year (the 6” and 9” groups grew ~4” more than the 12” group, and ~6” more than the 15” and 24” groups). This advantage did not, however, carry over to the field year. As can be seen in the figure below, all experimental groups finished at roughly the same height this past autumn. This means that once in the field, the 12” and 24” groups grew at almost double the rate of the 6” and 9” groups. The greatest gain was made by the 15” group, averaging 2.96” more growth than the 12” group. If this trend continues, the 15” group will average a foot taller than their 12” counterparts by their first potential year of bearing. The difference 3” of soil depth can have - at $.20 additional cost per tree, in our case - may be substantial.

Graph showing aerial height of groups in nursery and field year: Average Aerial Height Growth of Chestnuts (Nursery Year 2020/Field Year 2021) - Album on Imgur

Conclusive results remain to be seen, of course. Perhaps the trees in the 6” and 9” groups took their first year in the field to focus energy on expanding their limited root systems, and will now keep track with the other groups this season. Perhaps the 24” group will gain an advantage over time by virtue of a deeper root system. Time is needed to answer important questions related to survivorship, years to bearing, and overall health. Presently, our field planting is at 98.3% survival with only a single tree in each group dying. How will those numbers look after their first winter?

Photo of chestnut taproot: Chestnut seedling taproot. - Album on Imgur

The final report will be available mid-March on SARE’s website.


Did you factor in container width as well? I found chestnut seedlings grow faster in deep+wide containers compared to deep+narrow containers.

We controlled for width for the experiment using two ShellT grow containers connected together (at 6.25"). ShellT’s are meant to be grow tubes for deer protection, but I found this novel use particularly useful. Held them in bulb crates, which also provided them an air pruning bottom.

Being able to grow your seedlings in the nursery, then transplant them in the field with initial protection in place and only crates to carry out is an attractive idea we’ll be running with going forward. We’re starting our tomatoes in the tubes for market production now.

I did seed extra chestnuts in single ShellT containers (3.25" diameter) and was particularly impressed with the robustness of their root systems. If I had my choice, I’d go with 4-5" diameter (5.5" is achievable with two of these grow tubes, which is perhaps the best within the limitations of the product). As well, I’ll say the slit-ventilated tubes appear to be a better choice than the fully-ventilated option.


Welcome to the forum, this is an awesome study. Thank you for sharing! I know we have many interested in nuts who would be happy to follow the results @Barkslip @Fusion_power

Do you have any photos of the seedlings in the grow tubes or of the current plantings that you are able to share?

Edit: I see your photo log link.

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I do, yeah, as well as photos of the varying root morphologies produced in each depth of container. I measured root length as far as data collection, but this wasn’t adequate for capturing how different the groups were.

Will try to get photos posted soon.


Interesting research.
In the fall I bought some native chestnut seedlings … they had been in a flat of gro-mix
and no dividers … just scooped some up and potted 'em about 5 days later.
So far the one gallon pots appear ok…and the rootball reminded me more of blueberry than an oak or something.

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Thanks for presenting your preliminary results here Anson!

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Thanks, @BlueBerry, and way to get going on the native chestnuts. Hoping to get some American chestnuts on our farm eventually, but started with Chinese chestnuts as a better bet for commercial success. How old were the seedlings that you purchased? Signs of a taproot?

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Happy to finally contribute after lurking on here for a year!


Yes, I think just one yr. old. Not over 8 inches or so.
Taproot…probably. As not dormant, I didn’t try to ‘bare-root’ them.
Seed source Letcher Co. KY.
I also have 4 seeds collected in Jackson Co. Ky near an old cemetery…they have spent the
cold months in vehicle getting frozen and all.
The Am Chestnut society has enquired about my participation…but I think it’s not a priority just an interest for me. I don’t have time to plant chestnuts and enjoy the harvest.


I think that’s real cool that you have interest in American chestnut, @BlueBerry

best regards

@fullforkfarm try Roottrapper pouches/bags. Maybe call them and ask what they would recommend however it seems to me and I have some at home here that the 15" tall x 7" *I think7, would be the way to grow/go.

These things make “radical” differences in development of something such that @BlueBerry discusses shifting up a flat full of seeds, a flat with 5" or taller side walls, and then dropping them immediately into a 15 x 7 Roottrapper and (I believe) in one season you might see something spectacular that you would never expect! Give it a try…



Yes first year 4-in screened bottom flats for a few months and then uppotted to

10 in open bottom Air pruning bed gives a tremendously robust rooting system


Robust indeed!

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So when I uppotted to the deeper bed in the beginning of June the compost was still hot so the trees didn’t perform well… they actually got burned on top… the tallest was only about 18 in so the nice thing was I was able to store them a lot easier for winter. my hope is that when they get planted out this spring The Roots should really give them a great start. For comparison I did pick the best one from the 4-in flat and direct planted out so I could compare against the ones that were finished growing out in the beds. Next year and after.

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A guy in Pennsylvania direct sows American persimmon (no special source, just a generic) in good soil that’s loamy & uses a broadfork, first. Pinches the soil before he puts the seed in and from about May when he plants and at at the end of the summer, he averages 1/2" caliper and has 1" caliper. And 3/4" of course, too. But he’s shown me where he’ll get a few that are 1".

He uses organics I’m sure. That’s his nature… so it would be manure or pelleted chicken or similar.

The other thing is a simple raised bed w/o any kind of root pruning that sits 24" off of the ground and any type of “soil” fill may be used: with or w/o fertilizer; heavy 99cent top soil; peat-based, soil mixtures; it doesn’t matter. This was a university study at one of the Pecan Texas College/Universities that performed it. They said, ‘white rubber mulch’ and 24" of raised bed sown with pecan seed would produce (3-4’) seedlings in one season. I’m trying to remember but they all were 3/8ths or better… I’m certainly sure, that-much… the article for no-reason was removed and I saved it as a bookmark. Now when I find ‘special information’ like that, I snipping tool any of these and save them on Microsoft Word. That was a very informative study. I’ve reproduced it with pecans, too…

I’ve been growing in 30" Treepots for 18-months. I wanted Roottrappers, but I had already built a table for occupying 30" tall pots. I custom built my table for this. My thought was to grow a seedling and produce trees that can be 5 or 6 feet tall due to the length a tap-root would be able to continue too…

I decided recently that it would’ve been in my best interest to cut the pots off to 16". It’s not coincidental that you’re having success, your most-success, at 15" or believe that will prove the winner later, in a field-growing-situation. I could just see it in my mind after having raised seedlings of many things; I’ve grown in 5.5" x 2 3/8" Anderson Tree Band Pots starting 20-years ago and have tried all the Stuewe Treepot sizes and the 12.5 or 12" isn’t enough and the next thing is 30". I thought to myself before I decided on 16" that they would have an incredible Market for a pot that’s 20" - then eventually after having thought about it for another couple of weeks, I decided to “myself” that’s too much container and that 16 would be better.

I’ve grown in pots that have holes on the sides that are 12" tall and 5" across that taper to probably 3.5" or so. I’ve grown in Rootmaker square gallons; I can’t not tell you - what I haven’t already tried…

Raised beds I concluded were the best for ease of “lifting” seedlings…
Once the first row next to (a) wall, (maybe the second row) is lifted with a shovel, the rest of the work is wiggling the seedlings out of the media with your arms inside the soil and feeling around with your hands, or, some simply “lift up.” …they’re really simple to remove.

I just direct sow seed in the ground now. For anyone who cares, hardwood trees and shrubs grow their taproot where they “know” they won’t die during year one as long as they get water until mid-July. It’s programmed into hardwood-plants. So if you’re lazy and only water until mid-July, you can grow a tree that will likely outlive yourself. …since I do it mostly for grafting in place (nut trees) (persimmons) but it could be anything, it shaves years off of a potted tree trying to establish a taproot; however, what you see above from @Yarg is tremendous. It’s not nearly as good as Roottrapper believe it or not, but it’s SOMETHING SPECIAL he’s pulling off there. Roottrappers make roots just like @Yarg with the addition of fine hairs that are so dense that it looks like a wool scrubbing pad “dense” mat of fibrous material hanging from a million strings of spaghetti, just like Yarg’s roots.


You should try the Wayback Machine to find things like the article no longer available.

It’s gone though. The link after it stopped working still sent me to the Texas University but had a message that stated such as ‘this link no longer is available’…

I appreciate your efforts to learned me something new, however.

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Yes, that is the general concept.
The ones I got didn’t come from a flat that deep nor have that robust a root system…still the similarity is present. Looks about the same size. One year plant?

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Yes I started seed in 4-in flats first week of April, up potted first week of June and uprooted them November 18th.