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I'm going to plant two pecan trees. When I plant them, they'll just be pretty small, but will have an ultimate width of between 75 and 100 feet years from now.

Due to flooding issues, I would like to raise them up 8-12", and to prevent dirt from being washed away, I intend to essentially make an wooden raised bed, 2 1/2 ft square, 8-12" tall, and plant the tree on the top of that.

I'm hoping the root system as it grows will grow down and then spread out, but I wanted to double check that the roots won't be damaged by the constraints of the wooden raised bed.

Worse comes to worse, I can just unscrew and remove the raised bed after three years or so, but my question has to do with me leaving the raised bed boards permently in place.

Can I plant a tree in a open-bottomed raised bed, even if it's from a larger tree species?

Jamin Grey
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    A growing tree is more likely to destroy your raised bed than suffer any harm itself. A tree's roots tend to spread our horizontally just under the surface a little further than the extent of its branches. Either the roots will be constricted by the raised bed, which would affect the tree's stability, or more likely they'll find a way out, either over, under or through the sides of the raised bed. I guess you'd prefer them to go under, in which case the raised bed would be a bit moot. What's the nature of the flood risk? How is the surrounding area landscaped (is it paved, asphalt, etc?) – David Liam Clayton May 12 '17 at 08:47
  • It seems to flood annually, for a few days. I lost a couple trees in previous years, but others that were on ground just a few inches higher have done well. The surrounding area is grass and forest. It's planted between a mini forest and a grassy field. I'd like to keep planting in this location, if I can keep the trees alive long enough to get established. – Jamin Grey May 12 '17 at 08:56
  • Surely the ground where the tree's roots are will be saturated, whether or not the tree is planted on a raised bed? (assuming the tree's roots won't stay in the raised bed but spread out beneath it). If you think that soil washing away will be an issue then you could cover it with landscaping fabric or plant some ground cover plants whose roots will bind the earth (might be hard directly under a tree). I'd also try to ascertain the flooding tolerance of pecan trees - different trees will have differing abilities to cope with sitting in water (presumably we're talking about fresh water). – David Liam Clayton May 12 '17 at 09:52
  • http://msue.anr.msu.edu/news/flood_tolerant_trees – David Liam Clayton May 12 '17 at 09:53
  • It seems to me, as an gardening newb, that if there is standing water on the trunk - even just an inch up - or if the ground around the root ball is hyper saturated, it greatly reduces the chance of survival. If the trunk and rootball are lifted above the flooding, I *think* it'd greatly improve survival, and also reduce the number of days that the ground is soaked - seeing that the higher ground will dry first. Roots will ofcourse descend down into the flooded level, but that'll take a year or two of growth first, and the bigger the root system, doesn't it become more resistant to drowning? – Jamin Grey May 12 '17 at 14:23
  • That is all just hunches and assumptions without knowledge on my part! Please correct any false assumption I have. You are correct that I definitely should have checked flood tolerance before ordering trees. Oops! I checked planting distance, zones, and cold-hardiness, but flooding hadn't even occured to me. – Jamin Grey May 12 '17 at 14:27
  • Oh, to clarify, the "flooding" is like six inches above ground level at worst, and rapidly drops to an inch of standing water for two days or so. This may actually happen several times during the rainy season. I'm not talking about like several feet of water or anything. The top of the raised bed would be high enough to be above the flooding by an inch or two, and above the 48 hour post-flood standing water by six inches or so. – Jamin Grey May 12 '17 at 15:06
  • @JaminGrey can I ask how you got on with this. I have exactly the same problem and was thinking to build something like this: https://lda.lowes.com/is/image/Lowes/ht_build-a-stone-raised-planting-bed-hero?scl=1 – James Harcourt Jun 19 '20 at 18:23
  • @JamesHarcourt For some tree species it worked well, for others, it still got too much water and drowned the trees. Cherry trees and apricots seemed especially vulnerable to waterlogging. I've had to plant more, and always at higher ground. Complete deaths. Pecans have done okay (I lost a few, but could've been for unrelated reasons). Apples have done well (if raised up), Peaches, Pears, and Plums have done fine when raised. (though not all of my trees are at fruiting age yet, but they seem healthy in terms of trunks and foilage) – Jamin Grey Aug 10 '20 at 04:15
  • @JamesHarcourt Part of the issue was the moving water would erode dirt from my boxes, so trying to make it partially water-tight (at least in the direction the water is flowing from) helped greatly. Another issue - in my case, but not in yours - were my boxes floating upward. I've taken care of that by pounding nails in the sides and pouring a small amount of concrete around the bottom, both to block water and prevent erosion from the bottom. – Jamin Grey Aug 10 '20 at 04:18

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