Root barrier for new plantings

[Taupotreeman]

I know sweet fanny adams about root barrier despite spending hours trawling through Google so if anyone can help?

 

Council are planting new trees on a street upgrade.......again. The last trees we had put in with a tree spade had root barrier encircling the roots at about 1m to 1.5m out from the trunk. We had it moved to 2m to 2.5m out to give the roots a chance to re-establish. The trees had no irrigation and two of the four shed at least 60% of their leaves before we finally got approval for a soak hose to be installed. We are now planting Quercus coccinea in a similar fashion for the second upgrade. Irrigation is to be installed along with the same root barrier at 2.5m cube. My queries are; the trees will be growing in a pumice pit (due to layer upon layer of ash deposits from volcanic eruptions) so the roots cannot grow down, as in some cases with root barrier. Council is wanting full size specimen trees. What will the effect of the barrier be on the root growth? Will the trees be limited in size (presumably they will be) because of what will basically be a root barrier on all sides including under?

[Gary Prentice]

Flicking through the index of "tree roots in the built environment" no answer immediately becomes apparent. I'll spend a bit more time later in searching.

 

But to add another factor into the equation, none of manufacturers give any guarantee to durability over twenty or thirty years. Moffat did some research into this, so might be worth googling.

[Goaty]

I think long term trees do penetrate fabric barriers, only one one needs to break out then it becomes a primary root. As for barrier effect on root growth the plant will fill the cube as it would a pot. Then start to starve and grow less vigorously.

It will remain stable for a considerable length of time as the cube wedged with roots will fix solid, long term they will break out, maybe not in your working life though.

When I next come to NZ I hope to stop in Taupo and look at all these problems you keep getting. Would like to see how it works out.

 

As for not growing down in pumice, I reckon Broadleaf trees will still put taproot through for tapping in to groundwater. They do in chalk and pumice has air pockets that roots will split, But Im only assuming

[Gary Prentice]

I just finished a long, detailed and referenced reply, before losing my internet connection.

From what I've been reading, due to the compaction in urban enviroments, in many situations, roots are restricted to the planting pit anyway. With an average pit only being only 0.9 cubic meters (1.2x1.2xo.6m) yours are huge. If I'm reading it correctly, your barriers are 2-2.5m radius. At 2.5 and only 0.6m deep, if my maths is correct, that would give a volume of 11.78 cubic meters.

 

A survey by Kew, on uprooted trees, showed Oaks had a high proportion of roots up to 2m deep. It, the survey, didn't differentiate between species. So could the pits be deeper?

 

I think they will probably do okay, to a degree. Certainly not growing for 500 years, but an average life expectancy for urban trees is only 20-30yrs anyway. They have probably a better chance than most planted in hard surfacing anyway.

[Taupotreeman]

The main reason for the root barrier is to stop lifting of the footpaths, a common problem in Turangi because of the pumice. Roots seem unable to break through the pumice (believe me, it is several metres deep) so tend to grow along the surface a lot as the only good soil is about 0.5-1.0m deep. The pumice is like rock in most places. Most of the town's street trees are Pin Oak and Scarlet Oak and were planted in the 60's during the town's building for the hydro scheme. They are now around 20+m high. The new planting s, it is hoped, will grow to the same size as the existing trees. I am concerned about the trees starving, growth rates and stability with the root barrier.

Thanks for the replies so far, all good stuff.

 

 

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[Taupotreeman]

I think long term trees do penetrate fabric barriers, only one one needs to break out then it becomes a primary root. As for barrier effect on root growth the plant will fill the cube as it would a pot. Then start to starve and grow less vigorously.

It will remain stable for a considerable length of time as the cube wedged with roots will fix solid, long term they will break out, maybe not in your working life though.

When I next come to NZ I hope to stop in Taupo and look at all these problems you keep getting. Would like to see how it works out.

 

As for not growing down in pumice, I reckon Broadleaf trees will still put taproot through for tapping in to groundwater. They do in chalk and pumice has air pockets that roots will split, But Im only assuming

 

I'll shout you a beer and show you around when you're over.

 

 

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[Ms2004life]

Have similar problems here with rock instead of pumice and we have broken rock out lower down to allow roots to grow out at lower levels have found the biggest problem to be that once the trees are large they'll start to lift paving anyway as the root collar gets big the space thats afforded them originally isn't nearly large enough. The digging out is time consuming but it seems tohelp the roots lower. Hope im making sense

[Goaty]

I'll shout you a beer and show you around when you're over.

 

 

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Thanks, I've only dashed through Taupo on new years eve to catch the only interislander ferry booking we could get once. Then the next time went to Jet boat.

 

And nicked a bit of pumice floating on taupo for feet, still use it.

[Taupotreeman]

The attached photos show the last lot of transplanting and the root barrier. The barrier has since been moved out to give the roots some room to establis. We are finding that roots will not penetrate the pumice level because it is so hard and deep. They call it a pumice pan. There is no soil below for, in places, over a 100m, and in Taupo and Turangi for as far as you can dig after the first meter pretty much. I had a fence put in at home and they hit pumice less than 0.5m down when digging holes for the strainers. Working on the basis that the root barrier is to encourage the root to grow down but the pumice pan prevents this...........are we just going to end up with stunted trees?

[Taupotreeman]

I just finished a long, detailed and referenced reply, before losing my internet connection.

From what I've been reading, due to the compaction in urban enviroments, in many situations, roots are restricted to the planting pit anyway. With an average pit only being only 0.9 cubic meters (1.2x1.2xo.6m) yours are huge. If I'm reading it correctly, your barriers are 2-2.5m radius. At 2.5 and only 0.6m deep, if my maths is correct, that would give a volume of 11.78 cubic meters.

 

A survey by Kew, on uprooted trees, showed Oaks had a high proportion of roots up to 2m deep. It, the survey, didn't differentiate between species. So could the pits be deeper?

 

I think they will probably do okay, to a degree. Certainly not growing for 500 years, but an average life expectancy for urban trees is only 20-30yrs anyway. They have probably a better chance than most planted in hard surfacing anyway.

 

Interesting. The landscape architect and the community board are hoping that the new plantings will eventually reach the same size as the existing mature Oaks throughout the town. My concern is/was that that because of the barrier the trees would not mature to the same kind of degree. Apologies if I'm covering old ground but I need to ensure we get this right BEFORE the trees go in the ground otherwise, once the landscape architect has signed it off, if it doesn't work as planned then it'll be my fault