Lifting for final planting

Length of time in nursery

Ideally, a tree nursery should contain no native deciduous broadleaves older than 2 years, as this is the optimum age for planting out to ensure quick and successful establishment. On sites where growth is slower, 3 years growth (2 + 1) may be necessary. Any trees older than this are effectively being checked in their growth, and the longer they are grown in the nursery, the greater the problems of establishment when finally planted out. Each extra year spent in the nursery also takes up an increasing amount of space, and requires additional work of weeding, watering, transplanting and so on.

In practice, the vagaries of seed supply, germination and the demand for trees will mean that it is very difficult to use every tree at the optimum time, and some further growing on in the nursery is almost inevitable if you want to have a range of species available for planting most years. However, there is a time to cut one’s losses, and any broadleaved trees older than 4 years that cannot be found homes are best dug up and disposed of.

Yew and juniper, and the broadleaved evergreen holly are best grown in containers, and planted out when 2-3 years old. Scots pine can be lifted bare-root, as for broadleaves.

Plant dormancy

Plants are most tolerant to the stresses caused by lifting, handling, storage and transporting when they are fully dormant. Dormancy is indicated when plants have stopped growing, and next year ’s buds have hardened or ‘set’. leaf fall occurs with most species, but not all. The most accurate way of testing for dormancy is to carry out a physiological test of plant dormancy status, which may be used in commercial nurseries to indicate safe lifting dates. For details see Forest Tree Seedlings (Morgan, Forestry Commission, 1999).

The onset of dormancy is influenced by seed origin, nursery treatments and seasonal conditions. Undercutting and wrenching both induce dormancy, while fertilising prolongs plant growth. Plants become dormant earlier in the north of Britain than in the south because of cooler temperatures. Dormancy, and hence lifting dates may be brought forward or delayed, depending on the prevailing climatic conditions.

Shoots become dormant in response to day length and air temperature, while root activity is affected by soil temperature and soil moisture. Roots can continue to grow for up to one month after shoot growth has stopped and buds have set. In Britain it is rare for shoots and roots to be fully dormant before the beginning of December.

Release from dormancy, or dehardening, follows a period of exposure to cold temperatures during winter. This chilling requirement differs between species and seed origins. Plants take less time to break bud the longer they have been exposed to low temperatures. Trees only begin to grow when dormancy is released and temperatures increase during the spring.

The ideal ‘window’ for lifting and planting out may be very short, according to the time of dormancy, bottlenecks in supply, available labour for lifting and planting, the short daylight hours in winter, and other factors. Climate change is delaying the onset of dormancy and bringing forward the date of bud burst, but is allowing more planting to take place in December and January, which used to be too wet or frosty.

The following table, based on information in Forest Tree Seedlings (Morgan, Forestry commission,1999), gives a guide to the best lifting and planting out dates for bare-root broadleaved trees.

Lifting and transporting

Follow the instructions for lifting and transplanting. Note the following:

• Damage roots as little as possible.
• Don’t work in wet or waterlogged conditions, as if the plants are stored wet in sacks, mould may develop on the shoots. The roots should not be stored with large clods of wet soil attached, as this can physically damage the roots and restrict their oxygen supply.
• Allow excess soil to drop off, but do not shake or knock the plants to remove more.
• Place plants immediately in a special plastic sack (see suppliers), which is white on the outside and black inside, and seal the top as soon as the sack is full.
• Handle the sacks gently, and do not throw, drop or stack them.
• Store temporarily in a cool, shady place, between 0 and 5˚C. Do not allow them to heat up in sunlight.
• Store upright, not piled up on each other.
• Plant out in final site as soon as possible.
• If immediate planting is not possible, plants stored as noted above will not deteriorate if stored for a few weeks.
• Root dips, such as Broadleaf root Dip, may help reduce root desiccation and improve planting out success.

Heeling in

As necessary, heeling in can be used in order to free ground in the nursery for transplanting younger stock. The plants can be lifted in late October when the dying foliage is still attached, but before the onset of full dormancy. Plants will undergo the normal changes in dormancy during the heeling in period. This also allows the foliage to drop off before the plants are packed in sacks, to avoid problems with mould.

Choose a part of the nursery which has light, freely draining soil. Heavy, waterlogged soil will damage the roots. Never use water-filled ditches or similar for heeling in. Trenches should be dug as shown to the correct depth for the root system, and with a sloping back. Good soil to root contact is very important, as air spaces will cause the roots to dry out. Plants can be heeled in singly, or in loose bundles. If using bundles, make sure that the soil trickles through into the centre of the bundle. See diagram here.

Packing in sacks

Bare-root trees lose moisture through the shoots, even if the roots are wrapped, so this type of packing is only suitable if plants are being immediately delivered and planted. Otherwise, all bare-root stock should be packed and transported in sealed plastic sacks large enough to include the whole plant. If plants are too large for the sack, invert another sack over the shoots and seal to join the two sacks. Clean, thick black plastic sacks are okay for storage for 24 hours or so, but for longer periods, use special co-extruded planting sacks which are white on the outside and black on the inside, to prevent the plants from heating up.

Aim to sort and pack the plants so that the sacks don’t have to be re-opened until immediately before planting. Immediately after lifting, put the unsorted plants straight into plastic sacks and take them to a cool shed for sorting. Sorting in a cool, still, moist environment, rather than outside in the sun and wind, lessens the damage to the roots.

• Discard all diseased, spindly or damaged plants, or those with inadequate root systems.
• Cut roots longer than 15-17.5 cm (6-7”) long.
• Quickly bundle and tie the plants into bundles of 5 or 10, according to plant size. Tie loosely with soft string, as tight rough bindings will damage the soft bark. Attach a label to each bundle, showing the number and species.
• Put one or more bundles into the sack, with the shoots facing upwards.
• Gently squeeze the sack to expel excess air, and then seal the top by folding it over and taping it. label the sack.
• Handle the sacks carefully. Do not throw, drop or trample them, or stack them in piles. Store them carefully in an upright position, but not jammed tightly together. Tape over any tears or holes that occur.
• Store the sacks in a cool position out of the sunlight. For storage (fully dormant plants) for up to three weeks, use an unheated shaded building in which the temperature fluctuates as little as possible. Cold storage at +2˚, or freezer storage at -2˚is used in commercial nurseries.
• Keep sacks cool during transport. If stacking is essential to transport the plants, lay the sacks flat and stack no more than four sacks high.