What are Cell Grown Plants?
Cell Grown Plants (CGP's)
are grown in small containers called cells. Multi-celled trays hold compost into which
tree seeds are sown. The plants are grown with the trays being supported above the ground,
allowing air pruning of the taproots and root tips. This ‘pruning’ promotes
further fibrous root development, the key to future survival of a plant. Physical ridges
on the individual cell walls prevent any root spiralling, and train the roots downwards.Cell
grown plants are extracted from their cells prior to despatch and are wrapped in protective
packaging to ensure the root plug stays moist. The plants are planted with a completely
intact, fibrous root system, which minimises stress, and ensures good survival.
Traceability, from seed
collection to planting
The lifecycle of Cell Grown Fagus Sylvatica (Beech)
at Cheviot Trees.
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| 1.
A
mature quality seed stand from which seed is collected. |
2.
A newly sown tray of seed. |
3.
After a few weeks, the trees start their second stage of growth. |
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| 4.
Seedlings are now growing well and are regularly checked for pests, diseases and growth. |
5.
Trees have now matured and developed well. Having achieved a good root to shoot
ratio, plants are moved outside.
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6. At ordering, plants are hand graded to customers specification and are packaged ready for
despatch. |
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| 7.
At despatch the orders are checked and labeled ready for delivery. All relevant
paperwork accompanies the order. |
8. Quality plant production ensures healthy vigorous growth to
maturity. |
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Did you know? -
60% of forestry planting stock world
wide is now Cell Grown.
Why Have a Specification?
To provide guidance to specifiers and field practitioners
on the way to ensuring that plants are correctly specified, with reasonable requirements
being presented for nurseries to tender against, and that the plants actually supplied do
indeed meet these minimum quality standards.
What Quality Standard Are We Trying to Achieve?
Whilst this guide deals only with Cell Grown Plants, the
information presented is a summary of plant quality standards compiled by the Forestry
Group of the Horticultural Trades Association and is in line with official EU standards on
plant quality. Full details of the standards are available from the secretary of the
forestry group of the HTA.
Are Specifications Absolute?
Not necessarily. Seasonal variations, differences in
nursery practices, geographical location and genetic variation provide a complete spectrum
of possible plant sizes. Not all grades of stock will be available every season. And when
dealing with shrub species, such as roses and thorns, the nurseryman will often cut these
back to non standard sizes to promote strong growth and better form. A grading of 15-30cms
for cut back stocks may fall outside these proposed specifications but the plants may be
entirely suited to their purpose.
What Parameters Are Used?
Given that the plants are healthy and vigorous, CELL
VOLUME, HEIGHT and ROOT COLLAR DIAMETER are the accepted key criteria in drawing up the
specification laid out on the following panel:
Specification Guidelines
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British Standards
|
Species Group |
Minimum Cell Volume (cc’s) |
Minimum Root collar diameter (mm) |
Height Band (cm) |
|
Conifers
|
50 |
3 |
10/20 |
|
100 |
4 |
20/40 |
|
200 |
6 |
20/40 |
|
300 |
8 |
40/60 |
|
Birch, Willow
|
100 |
3 |
20/40 |
|
150 |
4 |
40/60 |
|
200 |
5 |
40/60 |
|
300 |
8 |
60/90 |
|
Alder, Beech, Blackthorn, Cherry, Hawthorn, Rowan, Sycamore, Crab
Apple
|
100 |
4 |
20/40 |
|
150 |
5 |
40/60 |
|
200 |
6 |
40/60 |
|
300 |
8 |
60/90 |
|
Holly
|
150 |
5 |
10/20 |
|
150 |
7 |
20/40 |
|
300 |
9 |
40/60 |
|
Ash, Hazel, Oak, Sweet Chestnut
|
50 |
5 |
15/30 |
|
150 |
6 |
40/60 |
|
200 |
6 |
15/30 |
|
200 |
8 |
40/60 |
|
300 |
10 |
60/90 |
Notes: Root collar diameter
is measured at the base of the stem.
Recommended minimum cell
volumes are those considered necessary to achieve satisfactory proportions
and shoot/root ratios.
The above table is intended
to cover the majority of stock raised in cells by British nurserymen. On
occasion, to meet specific requirements, it is possible that other cell
sizes and root collar diameters may be acceptable—or indeed specified.
Please ask for advice on non-standard specifications.
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Frequently Asked Questions
about Cell Grown
Plants
Q. Can whip sizes (60-90cms) be supplied in Cells?
A. The usual sizes grown in British nurseries are up to
40cms for Conifers and up to 60 cms for Broadleaves. There is no perceived advantage in
growing conifers (other than Larix species) in cells to sizes greater than 40cms. Larger
broadleaved sizes (60-90cms) can be grown, and nurserymen will grow these to
specification, and usually on contract, in larger cells.
Q. How are the plants delivered?
A. The cells in which the plants are grown usually remain
on the nursery. The plants are taken out of the cells and bundled together with the root
systems protected by plastic wraps for delivery. Variations in the cell sizes used in different
nurseries mean that blocks vary in the number of trees contained in a packaging unit
— common figures are 12 for broadleaves and 20 for conifers.
Q. Do Cell Grown Trees require special field protection?
A. No. If Cell Grown Trees have been obtained from a
reputable nursery they will have been fully hardened. They require no protection other
than that which would normally be given to any type of similar sized stock in the
particular planting situation.
Q. Can Cell Grown Plants be planted all year round?
A. It is advisable to avoid the period immediately after
the young leaves have fully opened in early summer. The plants have a very high water
demand at this time of year. Once the waxy cuticles on the leaves have hardened, planting
into most soils should be possible — but remember, the plants are not completely
drought resistant!
The Handling and Planting of Cell Grown
Plants
If the benefits of using Cell Grown Plants are to be
fully realised, it is important to recognise that the final planting out can be the most
vulnerable stage and root systems can be irreparably damaged if adequate care is not taken
with the storage and planting of the plants themselves.
Remember
- Cell Grown Plants are living things, and that whilst
the root plugs provide a degree of protection, they will die, just like any other plant,
if allowed to dry out.
- It can take the nurseryman up to two years to build a
fibrous root system, and careless aftercare two minutes to destroy it!
On receipt of the trees, if they have arrived packed in a
box, the boxes should be opened and the trees stood upright if there is likely to be a
delay in planting. Trees received during the dormant winter months can be held for several
weeks in the boxes. Once the trees have become active they should be stood upright as soon
as possible.
If Cell Grown Plants arrive on site, not boxed and standing
upright, they should be stored in a sheltered location if possible. This will reduce water
loss, even deciduous trees will draw some water from the cells in the dormant
season. The leeward side of a wall or a few bales of straw are all that is required.
However the plants are received, they should be kept moist, the principle being to protect the trees from physical damage and desiccation.
When the time comes to plant, the trees should be carried
on site in a method that will provide adequate protection. Purpose designed Harnesses are
available which minimise damage to the root systems and provide enhances establishment
— ask your nurseryman for details.
The type of tool
used for planting is largely a matter of
personal preference. However, the uniform and compact nature of the root plug does mean
that a smaller spade than is used for bare-root stock can be used. Whichever tool is used
it is important to ensure that the top of the root plug is covered by at least 1-2cms of
the planting medium and the soil firmed around the rootplug.
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