Arboretum Tree Planting Specification This specification has been produced in order to standardise tree planting techniques in the arboretum at RBG Kew and is supported by scientifically-based information on the factors affecting tree establishment, plus assessments made on site in the Arboretum 1.0 TIMING 1.1 Bare root and rootballed stock - September to April inclusive. 1.2 1.3 1.4 1.5 1.6 1.7 2.0 Container grown stock including Airpot material- September to May inclusive. Evergreen material September/November or March/May. Magnolia spp. & cvs. April/May Eucalyptus spp. June /July. Preference for planting is during the autumn/early winter period. Planting should never be carried out during periods of hard frost or when snow is on the ground. THE PLANTING HOLE 2.1 A circle of turf will be removed, 1.5m diameter, minimum: increase diameter for 2.2 2.3 2.4 larger trees. A square hole will be dug within the circle, to a depth of the rootball or a minimum of 300mm, i.e. a spit depth. Research has shown that wide rather than deep planting holes result in better tree establishment (ref. Whitcomb 1987). It is also thought that root penetration outside the tree pit is quicker and easier through the corners of a square hole rather than round (Ref. Kirkham 1990). For semi-mature trees, the tree circle will be a minimum of 3m diameter and the depth of the rootball. Soil removed from the tree pit will be put back and no new soils will replace the backfill removed. Due to the variation of soil throughout the Arboretum, the conditions of the soil should be assessed and organic matter should only be added to the backfill around newly planted trees if the soil is of a very poor quality, resembling builder s rubble. It is important that the compost when used is adequately mixed with the excavated material prior to back filling (Ref. Hodge 1990).
2.5 The prepared tree pit can, wherever possible be left fallow for a period before planting to allow for natural precipitation to permeate the site prior to planting. 3.0 PRELIMINARIES TO PLANTING 3.1 Evergreen material can be sprayed with an anti-desiccant spray such as Wiltpruf or S600, one day prior to lifting plants in the nursery. 3.2 With container grown and containerised plants that may be dry, the rootball can be thoroughly soaked prior to planting, by submerging the container in a tub of water until all air is expelled from the compost. This operation should be carried out the day before planting. 3.3 Check that the plant is clearly labelled. 3.4 It is important to take precautions to prevent the roots from drying out during lifting, transporting to the site and prior to planting by covering the root system with root wraps or placing the root system in a black bin liner or planting bag. (Ref. Insley 1979). 3.5 Examine the tree and prune out any damaged or unwanted branches or roots. 4.0 PLANTING THE TREE 4.1 The tree should be placed upright in the centre of the tree pit and the roots spread out around the hole in order to encourage them to grow out to the corners of the square pit. Where plants have been grown in containers, the roots should be teased out and encouraged to grow outwards. 4.2 Planting depth is critical; planting too deep is the cause for a high percentage of the small losses in an Arboretum. The root collar/hypocotyl should be level with the surrounding ground. By using the shallow planting method, it is unnecessary to allow for settlement. 4.3 A mycorrhizal inoculant can be added to the area around the roots prior to back filling; the application rates will depend on the product in use at the time and the size of the tree to be planted. 4.4 The backfill should be firmed evenly around the roots of the tree. Care should be taken not to compact on or around the roots. Brittle-rooted plants such as magnolias can be damaged by heavy firming and are best settled by light kneading or watering in.
4.5 4.6 If the site is thought to have poor, dry soil conditions, a water retentive material/agricultural polymer can be incorporated into the backfill at a rate of 160 grammes per planting hole. It is important that any water retentive material is thoroughly mixed before back filling, to avoid swelling and subsequent heave of the plant. All newly planted trees must be checked regularly during their first season, especially after windy conditions. 5.0 TREE SUPPORTS 5.1 A stake will only be used where deemed necessary, dependent on nursery stock size. 5.2 Where small nursery stock requires support, a stout cane and the Max Tapener system or nursery tying tube will be used and the Arboretum used as an extension to the nursery. 5.3 Where the root size of a newly planted tree and cane does not provide adequate anchorage or support, the use of a short stake and a single tie will be used wherever possible. The stake will be round and extend to one third of the overall tree height, see fig. 1. (Ref. Patch 1987). 5.4 Only the buckle ties provided will be used with the appropriate buffers and should be fastened no more than 30mm from the top of the stake. Any lower and this will allow the tree to chafe against the top of the stake. For large trees, use a nail through the tie into the stake, to prevent the tie from sliding down or around the stake. Leave approximately 5mm of the nail protruding to allow for easy adjustment during the growing season. Short vertical stake Single tree tie with buffer Between stake and tree
Fig. 1. Short Staking 5.5 Where it is not possible to use a single stake, i.e. a rootballed tree or bent trunks, the following two methods can be adopted, see fig. 2. Tie the stake at 1/3 tree height With tree tie and buffer
Fig. 2. Oblique Staking Crossbar Staking 5.6 Underground earth anchors may be used on extra heavy, root balled nursery stock. 6.0 MULCHING 6.1 If planting is carried out during a dry period, ensure that the tree is irrigated prior to applying the mulch. 6.2 The tree circle will be mulched with the woody mulch, taking care not place it too close to the root collar, as this will cause the bark to rot and invasion by disease. 6.3 Ensure that a space of a minimum of 100mm is left free of mulch around the root collar to avoid contact of the mulch with the trunk. 7.0 7.1 7.2 7.3 PEST PROTECTION Selected trees in woodland locations can be fitted with a semi-rigid expandable plastic tree guard (as provided) for protection from rabbits and squirrels, except trees grown for their ornamental bark. These must be checked for expansion regularly and removed or adjusted appropriately. Where mesh cages are necessary, the provided Netlon mesh will be used to the following specification: The cage will be 1 metre diameter and 500mm high, attached externally to 4 square stakes (50mm X 50mm) with the supplied electrical ties, using the template provided to set out the position of the stakes. The position of the top ties will be the 6 th square down and the lower ties will be the 6 th from the bottom. A central tie will be added to the join of the mesh on the back stake. 8.0 LABELLING See Label Specification 8.1 8.2 The new temporary nursery label, received after confirmation of transfer should be attached to the tree immediately, and all other labels removed. Should the permanent labels be available, they should be attached immediately following planting and the nursery labels removed. On larger trees the labels will be attached to a primary lateral branch, using the 2mm plastic coated wire, never around the main stem. If the tree is small or has no laterals
or is of a pendulous habit, attach the display label to a metal label stand and position at the front of the tree within the protective basket if present. The security label will be fixed to the protective basket behind the tree using a 400mm length of green plastic coated label wire. 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 AFTERCARE Once root anchorage has developed, the stake and tie should be removed immediately. Provided the soil conditions are suitable for root growth, this period should be no more than 18 months (Ref, Patch 1987) It is important to check tree ties regularly, especially after windy periods and adjust as necessary. For agricultural polymers to be of benefit to the survival and growth of newly planted trees, a regular input of water is required in order to recharge the product, therefore regular irrigation must be carried out during periods of drought. (Ref. Hodge and Walmsley 1990). Young trees will only be fed if needed from their second growing season in-situ every year until their fifth year. Organic fertilizer is currently being used at Kew, at approx. 40 grammes per tree. (Ref. Patch, Binns & Fourt 1984). The tree circle will be kept clear of weeds at all times, as competition for moisture and nutrients reduces survival and growth of newly planted trees. Effective weed control must free the tree roots from this competition. (Ref. Davies & Gardiner 1985). Only edges of tree circles in long sward areas will be edged by herbicide application. Tree circles in long sward areas will be maintained to a diameter of 2.5 metres to prevent competition for light and moisture. A tree circle will be maintained and kept weed free for a minimum of 15 years after planting and will not be grassed in unless the trunk is more than 250mm diameter. REFERENCES USED BROWN & KIRKHAM, T. 2004. The Pruning of Trees, Shrubs and Conifers, Timber Press. Revised & enlarged by T Kirkham. DAVIES, R.J. and GARDINER, J.B.H. 1985. The effects of weed competition on Tree Establishment. Arboricultural Research Note 59/85 ARB FLANAGAN, M. & JACKSON, A. 1990 Wakehurst Place Tree Planting Procedures (unpublished)
FLANAGAN, M & KIRKHAM, T. Tree planting at the Royal Botanic Gardens Kew and Wakehurst Place. RHS The New Plantsman Vol 2 Part 3 Pp. 142-151 (1995). HODGE, S.J. & WALMSLEY T.J. 1990 The Use of Water Retentive Materials in Tree Pits. Arboricultural Research Note 92/90 ARB HODGE S.J. 1990 Organic Soil Amendments for Tree Establishment. Arboricultural Research Note 86/90 ARB INSLEY, H. 1979. Damage to Broadleaved Seedlings by Desiccation. Arboricultural Research Note 8/79 ARB KIRKHAM, A.S. & ERSKINE, C.E. 1986 & 1993 RBG Kew Specification for Tree Planting Versions I & II Arboretum (unpublished) PATCH, D. 1989 Stakes and Ties. Arboricultural Research Note 77/89 ARB PATCH, D. 1987 Tree Staking. Arboricultural Research Note 40/87 ARB and 40/89 (revised) WHITCOMB, C.E.1987. Establishment & maintenance of Landscape Plants, Lacebark Publications, USA. Tony Kirkham: Head of the Arboretum & Horticultural Services Tony Hall: Manager of Arboretum and Arboretum Nursery Revised: January 2011