No. 3 Successful establishment of tree seedlings
NEW ZEALAND FARM FORESTRY ASSOCIATION INFORMATION LEAFLET
Introduction
Planting a tree seedling is easy – just dig a hole, place the roots in
the hole and cover with soil. Successful establishment of tree
seedlings so that they are still alive and growing vigorously a few
years later and grow on to become mature trees, however, requires a lot
more attention to detail. Good forward planning pays dividends, so
always plan just what you need to do well in advance of actual planting.
Key factors for success are:
- Make sure the species chosen is suitable for the site.
- Use good quality tree stock.
- Take great care in the handling, transport and storage of
seedlings.
- Ensure the planting site is well prepared, where possible
by deep cultivation with a winged ripper, and perhaps pre-plant
spraying with a weedicide.
- Plant seedlings as recommended in this leaflet.
- Prevent weeds from competing with the seedlings for at
least a year after planting.
- Protect seedlings from browsing by stock and wild animals.
Bare-rooted stock
Stock quality
Handling and storage
Planting
Basic principles
Time of planting
Container-grown stock
Weed control
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| The good quality seedling on the left has a callused
taproot and
abundant fibrous lateral roots that have been properly trimmed. The
seedling on the right has a bent, damaged taproot with only a few, weak
lateral roots. |
Watering
Staking
Animal protection
Bare-rooted stock
Bare-rooted stock are preferred to container stock for large-scale
planting because:
- they are usually much cheaper to produce.
- more seedlings can be carried when planting away from roads.
- it is difficult to produce container stock large enough and
sufficiently well conditioned to establish well on harder sites.
However, some species, particularly many of the eucalypts, perform much
better when container grown.
Stock quality
Under ideal planting conditions, small seedlings transplant better than
larger ones, with less interruption to their growth. In practice, a
minimum size is required because:
- the seedling must contain sufficient food reserves not only
to survive until planted, but also to make new root and shoot growth
after planting. Root collar diameter is the best indicator of food
reserves.
- the stem must be sufficiently hardened to withstand
handling and storage without damage, resist disease and insect attack,
and tolerate harsh weather conditions after planting.
- the seedling must be large enough to be planted deeply in
uneven ground without being buried, and to be able to cope with any
likely weed growth.
Recommended sizes for
bare-rooted stock of common species
| Species |
Min. root collar
diameter (mm) |
Desirable height (cm) |
| Radiata pine |
6 |
25-35 |
| Cypresses |
6 |
25-35 |
| Eucalypts |
8 |
40-60 |
| Douglas-fir |
10 |
40-50 |
| Blackwood |
10 |
60-80 |
To ensure that you get stock that meets these criteria, it is always
best to order seedlings from your
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Seedling
stem diameter and height are used to assess quality.
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nurseryman a year in advance, and if necessary, pay a premium for
quality stock. Be brutal about rejecting stock that doesn’t meet
specifications. Most farmers wouldn’t hesitate to reject inferior
animals when buying, but many seem prepared to accept poor seedlings
from nurseries, even chasing ‘bargains’.
Besides being sufficiently sturdy, seedlings should be of uniform size,
because planting a mixture of sizes will probably result in uneven
growth. Insist on uniform sturdy stock for harsh sites, but be prepared
to accept smaller stock (but still above the minimum size) if you have
easier sites. Seedlings should have major roots which are either
callused or cleanly cut, and an abundance of fibrous roots. The size of
the root system will depend on the size of the top, but for large-scale
plantings, the root systems should be no wider, and only half the
length, of the planting spade used.
(top)
Handling and
storage
Young seedlings are very vulnerable to physical damage, so treat them
gently.
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| Standard planting box. |
Lie seedlings flat for transport, because upright travel will bruise
the major roots and they’ll die back after planting. Ensure that the
roots are never exposed to wind or sunshine for more than a few seconds
from the time they are lifted in the nursery until they are replanted
in the field. If the ground is dry when seedlings are lifted, the roots
should be moistened immediately and kept moist – if allowed to dry out,
smaller roots quickly die.
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| The best method of transporting open-rooted stock is to
use planting
boxes in which trees remain from the time they are lifted in the
nursery to the time they are planted. |
During storage seedlings use up food reserves to respire, and
respiration increases dramatically with increasing temperatures, so
always keep seedlings as cool as possible, but don’t allow them to
freeze. If you store seedlings temporarily at the planting site, always
keep the packages out of direct sunlight, preferably in naturally
shaded areas.
Planting
The future root system of the tree is largely determined by the way the
roots are positioned at the time of planting. The commonest faults in
planting are:
- not planting deep enough. Such trees are much more prone to
topple in strong winds and to suffer moisture stress under dry
conditions.
- not creating a planting hole big enough to accommodate the
root system without distortion. Roots bent horizontally around the
lower stem will later strangle the main stem, resulting in wind throw.
If the nurseryman has not trimmed the roots sufficiently, use a sharp
pair of shears and trim the roots in a cool shady place before going
out to plant.
- dragging the roots into a planting slot so that they all
point in the same direction, resulting in unstable trees with ‘hockey
stick’ root systems.
(top)
Basic principles
- When planting shelterbelts on wet sites, create a raised
bed by cultivating the soil in dry weather and forming a mound with an
angled blade on the back of a tractor.
- Plant seedlings into cultivated or loosened soil. If the
site has not been deeply cultivated by ripping or bedding, cultivate
the site by hand at the time of planting so that new root growth can be
made into loosened soil.
- Plant seedlings so that the root collar is buried at least
5 to 10cm; this is particularly important on dry or exposed sites, or
where hand weeding is to be carried out.
- Make sure the planting hole is large and deep enough to
accommodate all the roots without bending or distorting them in any way.
- Spread the roots apart as much as possible with no tangles,
and cover them with loose soil. Lift the seedling 2 to 3cm while
shaking, to allow soil to filter between the roots and to ensure that
all roots are pointing downwards.
- Firm the surface with the sole of your boot, taking care
not to strip the foliage or branches from the stem while doing so. In
firming the soil, the aim should be to ensure that the surface is
sufficiently compact to stop the seedling moving in the wind, but not
to compact the soil too tightly round the roots, especially if it is
wet and/or heavy.
- Except on wet soils or high rainfall areas, leave the
seedling standing in a slight depression.
- When planting into ground which has been sprayed with a
pre-emergence weedkiller, take care to prevent surface soil from
falling into the planting hole.If the surface soil has been removed
before digging the hole, replace
it round the stem.
(top)
Time of planting
Bare-rooted seedlings should not be planted while they are actively
growing, particularly once they have started to flush in the spring.
Provided good hardened stock is used and the ground is moist, autumn
(April) is a good time to plant, particularly in low rainfall areas.
The warm soil allows the seedlings to develop new roots before winter
sets in, and the winter rains ensure that soil settles evenly round the
roots. However, autumn planting should not be used for frost sensitive
species, if the ground is at all dry, or if good careful lifting and
handling of the seedlings cannot be guaranteed.
Planting in May or early June is not recommended because seedlings then
have to withstand all the vagaries of a winter climate before they can
start to make new growth, and warm days can lead to winter desiccation,
i.e. the leaves dry out and there are no new roots to replenish their
moisture. Most planting is carried out in July or early August when
seedlings are dormant and can best withstand handling. The aim should
be to plant immediately before the soil warms up sufficiently for the
seedlings to make new root growth. In cold climates, it is better to
plant in late August rather than late June.
For sensitive species, planting is best carried out even later, after
the worst of the winter frosts are past, but before the seedlings have
started to grow.
For cold inland sites where planting is not possible before late
September or October, seedlings should be lifted as late as possible
before bud burst and held in a cool store until planting.
Container-grown
stock
Although container-grown stock can be planted out at any time of the
year provided the roots are not greatly disturbed, the conditions
required for successful establishment of bare-rooted stock are equally
applicable. In particular, do not plant containerised stock into dry
soil, or soil that is liable to dry out in the near future, otherwise
the potting mix the roots are growing in will rapidly dry out and kill
new root growth.
Side-slot air-prune containers are the best because theyn produce less
root distortions from roots deflecting off container walls.
Rootrainers®, or similar containers with ribbed sides are capable of
producing a "root cage" thus reducing the stability of the tree as it
grows. Always cut off the bottom 2-4cm of roots before planting. Stock
grown in other types of containers should be planted out before the
roots are greatly affected by the sides of the containers, otherwise
the seedlings will probably grow into unstable trees. In practice, this
means that
seedlings grown in small peat pots should be planted out when they are
very small, e.g. about 10cm high.
Small stock can give excellent results provided it is carefully planted
into well cultivated soil, given good weed and animal control, and is
sheltered from harsh conditions until it is well established. As such
stock is usually very soft, it is best planted in late spring when the
danger of frosts is past. Provided the soil is moist, it can then start
growing immediately and make maximum height growth before the following
winter.
Much of the larger container-grown stock obtained from nurseries,
however, is grown in planter bags. It is invariably root-bound to some
degree, often very badly. Slicing down vertically with a knife and
around the circumference of the root bundle helps, but the only sure
way to ensure the future stability of the tree is to remove the
container, gently shake or wash the soil out, tease out any tangled
roots, and trim off any long or badly twisted ones with a sharp pair of
shears.
(top)
Weed control
This is such a wide ranging subject, it is covered in a separate
leaflet. Suffice to say that without a doubt, in New Zealand the
greatest cause of seedling failure after planting is due to inadequate
weed control. Weeds are particularly adept at extracting moisture from
the soil, and have their greatest effect when conditions are dry.
Vigorous weeds can also overtop and smother seedlings, greatly
restricting their growing space.
For successful establishment, newly-planted seedlings require an area
of one square metre (1m2) around them to be kept weed-free for the
better part of one growing season, and for slower growing species,
including natives, a second season free of weeds will pay dividends.
Whether weed control is by grubbing, mulching, or chemical sprays is up
to the individual grower, but there are many effective chemicals
available these days, and spraying is the only realistic means of weed
control for large-scale plantings.
Watering
The best form of watering is perfect weed control. If you have to apply
water to keep newly planted seedling alive in a drought, apply about 10
litres/seedling at a time every few weeks, rather than much smaller
amounts every few days. In dry conditions, root growth is attracted
towards moist soil, and a heavy watering will attract root growth
downward as the surface dries out. Light watering only moistens the
surface, and root growth will be attracted to the surface. Do not use
drip-feed watering unless you intend to continue using it throughout
the life of the tree, and even then, trees will probably require
staking in windy situations because they will have unbalanced root
systems.
(top)
Staking
When planting large specimens of amenity trees, it is sometimes
necessary to stake them to prevent them blowing over in the wind. The
aim should be to keep the root system rigid until root growth can get a
good grip on surrounding soil, but to leave as much of the stem free as
possible so that wind movement will stimulate the stem to thicken up.
When staking, use stout stakes, driven in at an angle if the tree is
already planted so the root system isn’t damaged, and tie the tree to
the stake at no more than a third the height of the tree, preferably
lower. Use a soft broad tie (a strip of car or truck inner tube is
ideal) and make sure that the stem cannot rub against the stake.
Animal protection
No matter how well you prepare the site, and choose, handle and plant
your tree seedlings, all your efforts can be quickly ruined by animal
damage. Fences must be absolutely stock-proof, and if you have a
problem with rabbits, hares or possums, these animals must be
controlled before seedlings are planted, because they can do a lot of
damage in one or two nights. There are now several animal repellents
available for short-term protection, but to be effective they need to
be applied the day seedlings are planted, so that animals quickly learn
that the seedlings are unpalatable. For shelterbelt plantings, placing
a used car tyre over each seedling usually gives excellent protection,
but make sure it is removed after a year or two. For small-scale
plantings there are several forms of plastic tree guards available that
give good protection from wild animals. If tree guards are used to
protect against domestic stock, ensure that the guards are tall enough,
and very firmly staked.
(top)
(Graphics reproduced from Establishing a Small Forest –
no.5 in the Small Forest Managementmseries, jointly produced by the
Ministry of Forestry and the NZ Forest Research Institute. © Crown
Copyright Ministry of Forestry, June 1996.)
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