I have heard the fruit tree specialist from NC state mention that fact during just about every presentation I have attended on planting fruit trees over the last 15 years. It’s a common question from homeowners and new commercial growers too. The answer is always “do not add amendments to the planting hole”.
I’m not sure if planting an orchard in compacted fill dirt would change his recommendation, especially when planting Paw Paw trees rather than Apples or Peaches
My friends are on a tight budget so yes, maybe top dress is best.
I get why people keep asking. It sounds reasonable enough, and it used to be the widely accepted way of doing things. Once people get used to a certain way of doing things, it tends to stick. It also used to make more sense to leave the car running than to turn it off because of how much fuel was used at startup. Computer-controlled fuel injection makes that not the case, but people still think that it is, because that’s what they were taught!
Where are your friends getting their paw paw cultivars from? Virginia forestry dept has them going on sale October 3rd and Kentucky and Missouri already had their sale which lasted a few hrs before they sold out.
If they want cultivars the least expensive place is Northwood about $11 each in 5.5" banded pots. Pretty small, but they grow decently fast. www.northwoodsnursery.com they start paw paw sales July 1 and are almost out of most varieties now.
I totally agree, growing a tree is similar to growing a tomatoe plant, for best results you want to surround the entire root ball with good soil. Only a tree’s root ball is 1000x bigger than a tomatoe plant so it is a lot more $$$ and labor. Would love to see a university study done on this subject with real world results after several years.
They’ve done loads of studies, and the findings are that it’s almost always a bad idea. You’re better off filling with the same soil that came out of the hole, and putting any amendments at the surface. A tree gets most of it’s nutrients from the top few inches, and the deeper roots are there for anchoring and for getting water in dry periods.
This blog post does a good job enumerating the reasons why it’s a bad idea:
They grew their own seedlings plus I gave them a lot of seed for next year’s planting. Thanks though for the Va Forestry tip.
The fact that it did drain in 24 hours means I’d not lose any sleep over it. If you do keep adding chips…just make sure your plants roots are also in soil…or they’ll probably dry out at some point if the tree roots are in chips only.
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Ive read that website, but it’s not a study. it is merely a hypothesis without any research done. I am looking for an experiement where trees are planted in both amended and non amended soil with results 7 to 10 years latter. if you know of any like that please let me know.
Do you place any weight on the recommendations from a PHD level fruit tree specialist in NC who interacts with hundreds of growers on more than 10,000 acres of commercial fruit?
Sometimes no valid field trial is available and you have to do your own research.
Perhaps plant some Paw Paw of the same variety at the same time but using different amendment practices. Keep records and do the statistics. Probably have some useful information about tree growth in a few years. Could take a lot longer to generate useful information on fruit yield.
We have grown several acres of tree fruit in central NC at a profit for a good while. Not every recommendation we have received over the past 40 years from the PHD fruit specialists has been correct. I would guess they have been about 90% right. Their failures were mostly a result of something different in my soil and micro climate compared to growers a few hours away. Bud9 rootstocks and southern highbush blueberries are two examples of the failures.
Many university horticulture departments have planting guides written by their researchers, but I’m not talented enough at Google scholar or whatever to track down actual studies. This Clemson planting guide does say this advice is based on “research,” but it doesn’t include citations:
The authors:
People with Phd’s have been proven wrong many times. Just think about doctors who used to deliver babies and how much has changed from the 1950’s. So no I don’t care about their title. If growing trees in amended soil with surrounding clay creates roots that dont’ expand out then one can do a research study, dig them up and takek photos of the bad roots. I’ve yet to see even a study that shows the above ground part of a tree photographed vs a control group. If the phd person has planted trees with a control group sure I’ll listen, but otherwise it’s mostly a hypothesis,
I just looked more deeply and found a few. This 1993 publication, Tree Planting Fundamentals, which does include some citations to support the claim that backfill shouldn’t be amended with organic matter:
Here’s another more recent study of multiple species that also has a number of citations to other studies:
Soil Amendments at Planting
Here’s another one:
Effect of Planting Hole Size and Amendments on Growth and Establishment of Acacia farnesiana
After reading or skimming those, and a few of the references they cite, I’d say there are a few limited cases where amending may be beneficial, but if you can just amend whole rows instead of holes then that’s ideal in those cases. In most cases, the “hypothesis” has been supported that there’s at least no benefit in amending just the backfill, and likely harm in some cases.
It’s the decades of experience working with hundreds or perhaps thousands of commercial tree fruit growers and other researchers that makes their advice valuable. We are lucky to have a lot of these very experienced folks in NC. Many of them have a PHD from a top tier university known for excellence in tree fruit production like Cornell or Michigan.
Their advice is valuable but like I said its not perfect.
Ignore it at your own risk
Yes, I apologize that is not a link to original research. I choose to share info from that site because he does not speculate, but instead does a good job explaining the current state of research in ways that are easy to understand and apply. The author, Robert Pavlis, is one of the few sources whose claims I don’t need to interrogate too thoroughly, as I have come to trust he’s done his due diligence. He’s also willing to admit when he was wrong or to change his thinking in light of new research.
There is research that has been done with deep tillage of soils. The primary issue is that the results are very location specific. Soils and climate etc vary widely and what helps in one case might not in another.
In northern Texas a soil that was poorly draining clay to clay loam in the upper 4ft was mixed to 6ft depth. The lower 2ft was a friable caliche. Mixing was via a trencher so was a very complete mixing. After mixing the soil was much improved for growing both dryland and irrigated crops. Follow up was 40 years by the time I was involved and positive effects were still fully evident. No amendments were added.
I would not be afraid to mix the clay lake bed soil with organic amendments. I don’t think that would hurt long term suitability of the soil. But it might not help much.
What I think would help clay lake bed soil would be to add at least two parts sand to each part of clay. That would change the clay to a sandy clay soil with better drainage. Trouble is that’s what, 6ft of sand.
The other alternative would be to add a foot of organics and then mix the soil deep enough that there were equal amounts of lake bed clay and red clay in the final mix. If the red clay drains well it and the organics would help the lake bed clay.
I see a few problems that will hit hard in a couple of years.
The amount of wood chips on this soil will cause nitrogen depletion which is very detrimental to pawpaw. It is still a good idea to add the wood chips, just provide nitrogen to help it break down. You can add nitrogen two ways, either by planting a cover crop (hairy vetch recommended for your location) or by supplying commercial nitrogen fertilizer. It will take about 150 pounds of actual nitrogen per acre to fully decompose the wood chips already there plus the additional mentioned above.
Hairy vetch - and other plants - will not grow in wood chips. It needs some soil to get established. For this reason, I recommend using either chisel plow, tiller, or some other tool to mix at least the top foot of soil and chips. Given the amount of wood chips already there, you may have to go a couple of feet deep to get some actual soil to the top.
Earthworms live where the soil stays cool. If shaded by plants, the soil will be cool. If protected by wood chips, the soil will be cool. If it is open and nothing much is growing, it probably won’t be conducive to worm health.
There were suggestions above to avoid amending soil in the planting hole. This is valid, but misses the point. Amend the soil as needed for the plants you want to grow. A soil test will go a long way toward determining what needs to be added.
Micronutrients are likely to be in short supply, particularly zinc and boron. Zinc sulfate is available at most farm supply stores. Boron can be purchased as 20 mule team borax in most grocery stores where it is stocked as a laundry detergent. The other micronutrients that may be in short supply should be identified by the soil test. Magnesium and copper are two that often are crop limiting.
Other than that, what varieties are you planting?
thanks for the links, I also skimmed them and came away with a totally different conclusion:
Amending soil benefits depends a lot on the tree one is growing. Studies based on digging a tiny 18 or 24" hole are worthless to me becuase I plan on a bigger 4’-5’ diameter hole. And Amending soil when the soil is already good is a waste of time and money.
Just reading this small segment shows the varaiability when a 2x2’ hole is dug for trees in clay soil and amended.
Plant materials responded differently to the various treatments. Magnolia growth
after …3 years, amended + irrigation gave the greatest growth.
After 3 years the B&B dogwood plants showed … the treatments consisting of (1) mulch, amendment, and irrigation and (2) amendment + irrigation were significantly higher than other treatments.
The 2 treatments of mulch and native clay produced larger plants of bare root dogwood. After 3 years the amended + irrigated plants were significantly larger.
The growth of sugar maple also varied by years…mulched + amended + irrigated plants were larger after 3 years.
most surprising result is trees with out mulch blue boxes, did better with trees with mulch, except for surar maple.
Ideally I’d fine a study done just on paw paws in clay soil, but I doubt I will so I’ll be my own guinnea pig and try a few differnet methods.
yes I agree i will have to add nitrogen. I added synthetic nitrogen to a 40 yard cubic of wood chips and they are decomposing nicely and still warm after about 18 months.
Wild plants have taken over 80% of the 1/4 acre wood chip land after about a year. I’m surprised how fast nature comes back! On some other land that is more shaded the wood chips stop new vegetation very well.
I plan on a big mix of vareities mostly KSU atwood, benson, and susquehanna.
I think I will do above. Sand would be nice but very expensive. The lake clay loam soil has a decent drainage with some sand/silt in it.
