Tree Pit sizes

[benedmonds]

Can anyone point me in the right direction for information regarding recommended tree pit sizes. 

I have a site planted with 250 whitebeam in the early 1990's, many of the trees are now obviously past their best, many having been topped in the past, they were also apparently planted in precast concrete cylinders.  
 
The site is being redeveloped and I want to convince them not to specify crappy sorbus, but will need to ensure the tree pits are suitable. Currently they are talking about retaining some of the compromised trees but I think it might be better to replace with better trees.

[carlos]

i think soil quality would be worth checking, are they going to be bareroot or rootball?

hand dug or digger i find that is the biggest factor in root pit size!!

a bit bigger than the rootball and loosened up in the bottom a bit should be fine.

 

[dangb93]

BS 8545:2014 has probably all the answers you need.

Including;

The planting pit should be no deeper than the rootball or container depth. 

The pit should have a diameter at least 75mm greater than that of the root system.

Tree pit sides should not have compacted, glazed or smeared sides. Sides of the planting pit that have been smeared or smoothed during excavation should be scarified.

The root flare of the newly planted tree should be clearly visible at the soil surface. It should not be buried
by excess soil or mulch.

The backfill medium used should be as close as possible in texture and structure to the soil excavated from the tree pit. Ideally the soil dug from the excavated pit should be used as the backfill medium.

 

I was also taught to dig a square pit, rather than a round one - the roots will go round and round a circular pit and won't grow outwards.

 

21 hours ago, carlos said:

loosened up in the bottom a bit should be fine.

During the preparation of the tree pit, the soil is disturbed, but the base of the tree pit should remain undisturbed unless there are specific problems such as poor drainage, soil smearing or pans resulting from pit construction which need to be rectified.

 

 

[daltontrees]

Tree Species Soil Volume Guide - GreenBlue Urban

GREENBLUE.COM

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Initially published in 2019, the GreenBlue Urban Tree Species Soil Volume Guide was a brave attempt to give specifiers a...

Dangb93 covers it. The tree pit shouldn't really have to be much bigger than the rootball or container, as long as the roots are going to be able to penetrate and use the surrounding soil.

 

The green blue urban guide is about final voume. However, I have noted in the past that if you compare it with the volume implied by the root protection area in BS5837, the GBU volume is inadequate. 

[Dan Maynard]

Are you asking if they can go straight back in the containers in the diagram? They seem to have a very strange root shape on there.