Layering and grafting are vegetative propagation techniques for native plants. Layering involves bending stems to the ground to form roots while still attached to the mother plant, providing advantages like less maintenance than cuttings. Grafting joins parts from two plants so they grow as one, allowing benefits like changing varieties or taking advantage of particular rootstocks. Both techniques can help propagate native species when resources are limited.
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Layering and grafting
1. Layering and Grafting
for
Native Plant Propagation
Layering:
What is Layering?
Layering is a form of vegetative propagation where cuttings are made to form
adventitious roots while the cutting is still attached to the mother plant. Stems of the
mother plant are covered in a growing medium in various ways to exclude light, increase
the moisture level, and stimulate root growth. Once roots are formed the new plant
(layer) can be dug and transplanted to the desired location.
Layering is an ancient technique for vegetative propagation. It was used
extensively in European nurseries from the 18th
to the early 20th
century for propagating
woody shrubs and tree species. It is no longer a primary nursery technique for
propagating most plants, but does provide some advantages for propagating native
species where time or resources may be scarce.
What are the advantages of layering?
The advantages of layering include:
⢠Less maintenance than cuttings
⢠Allows propagation to be performed on-site
⢠Natural accumulation of photosynthates and hormones due to
girdling, incision, or bending
⢠Often times a large plant is the product
⢠Easy to do with little investment
Major Advantages or Restoration:
Less Maintenance
Unlike regular stem cuttings, those produced by layering are still attached
to the mother plant and therefore require less maintenance. Their supply of water
is not significantly decreased since they are still attached to the root system of the
2. mother plant. This eliminates the need for resource and labor intensive practices
such as shading or regularly misting of young cuttings. Layering also reduces or
eliminates the need to harden off cuttings before planting since they are already in
their native environment.
Propagating on-site
Layer can be done on site where there may be well established plants of a
species that you want propagate. Since layering usually consists of bending a
branch down below the soil line, often times the only required materials are a
shovel, and stakes to hold the branch below ground and to keep shoot tips upright.
This can seriously reduce the amount of time and resources needed in hauling
plants and supplies from place to place.
Disadvantages
⢠Takes a long time to produce new plants
⢠Produces only a few plants per mother. Not ideal for plants
that you want a lot of from only a few mothers, or for sites
where resources and time are not particularly in short supply.
Keys to Success
⢠Light exclusion form the rooting section of the stem is a must. If light
is allowed to penetrate root formation will not be successful.
⢠Girdling, incision, bending, or cracking the stem. Wounding the stem
in some form triggers the release of hormones and increases the
likelihood of successful propagation.
Types of Layers
Simple Layer â A type of layer where shoots from the previous year are
bent to the ground (sometimes girdled) and covered in soil and âpegged downâ 6-9 inches
form the tip. Shoot tips are left emerging from the soil forming a U shape. Shoots are
held in place using stakes.
3. Simple layer with stake holding shoot in place
Compound Layer - A type of layer in which entire horizontal shoots
are covered in media causing the formation of numerous rooted layers per branch rather
than just one.
Serpentine Layer - Just like a compound layer except that individual
nodes are covered with media. Generally there is an alternation where every second node
is covered. Most effective with plants that yield flexible shoots.
Serpentine Layer
Air Layering - Air layering is a technique performed without placing the
layered branch or shoot below the soil line of the mother plant. The stem is first girdled.
Proper girdle is key to causing the accumulation of carbohydrates at the cut. Then, the
girdled section is wrapped in media like peat moss that is easy to work with. Adding
hormone to the media or directly applying it to the stem is very beneficial. The media is
then enclosed in plastic and tied off. Once roots have formed the layer can be removed
from the mother and planted.
4. Sequence of air layering. Girdling, applying hormone, wrapping in media and
plastic, and tying off.
Mound Layering - A type of layering that is useful with heavy-stemmed,
closely branched shrubs. For a mound layer cut the plant back to 1 inch above the soil
surface in the dormant season. The dormant buds will produce new shoots in the spring.
Mound soil over the new shoots as they grow. Roots will develop at the bases of the
young shoots. Remove the layers in the dormant season and either place in containers or
transplant diriectly.
A mound layer well into the growing season
Tip Layer - Tip layers are a very quick way to layer a lot of branches. The branch
of the existing mother plant are bent down to the ground and the tips of the branches are
essentially buried in 3-4â deep holes. The shoot naturally grows into a U shape with
roots developing at the bend. Remove and plant tip layer in late fall or early spring.
5. Tip layer with a Rubus species
Good Natives for Layering:
Layering is most effective on plants whose branches can be easily bent
down to the ground or plants with ground hugging stems. It has been noted to
work especially well with salal, kinniknnnik, twinflower, tailing honeysuckle,
which have ground hugging stems. Layer has also been effective with snowberry,
Indian plum, Oregon box and other plants whose stems or branches can be easily
bent down. The literature on layering natives is quite thin, but it has a good
chance of working on any plants with the above characteristics.
Grafting:
What is grafting?
Grafting is a horticultural technique used to join parts from two or more plants so that
they appear to grow as a single plant. The upper part (scion) of one plant grows on the
root system (rootstock) of another plant.
Grafting can only be done between reasonably closely related plants. Most often the
limits of success are with other species in the same genus, though in some cases plants in
6. different but closely related genera can graft successfully (e.g. Larch will graft on
Douglas-fir), and in other cases, not, even between some species in the same genus (e.g.,
Norway maple will not graft on Sugar maple).
Reasons for grafting
Grafting may increase the productivity of certain horticultural crops because it makes it
possible to do the following things:
Change varieties or cultivars. An older established orchard of fruiting trees may
become obsolete as newer varieties or cultivars are developed. The newer varieties may
offer improved insect or disease resistance, better drought tolerance, or higher yields. As
long as the scion is compatible with the rootstock, the older orchard may be top worked
using the improved variety or cultivar.
Optimize cross-pollination and pollination. Certain fruit trees are not self-pollinating;
they require pollination by a second fruit tree, usually of another variety. This process is
known as cross-pollination. Portions of a tree or entire trees may be pollinated with the
second variety to ensure fruit set. For example, some hollies are dioecious, meaning that
a given plant has either male or female flowers but not both. To ensure good fruit set on
the female (pistillate) plant, a male (staminate) plant must be growing nearby. Where this
is not possible, the chances that cross-pollination will occur can be increased by grafting
a scion from a male plant onto the female plant.
Take advantage of particular rootstocks. Compared to the selected scion, certain
rootstocks have superior growth habits, disease and insect resistance, and drought
tolerance. For example, when used as rootstock for commercial apple varieties, the
French crabapple (Malus sylvestris, Mill.) can increase resistance to crown gall and hairy
root. Malling VIII and Malling IX are used as dwarfing rootstocks for apple trees when
full-sized trees are not desired, such as in the home garden.
Benefit from interstocks. An interstock can be particularly valuable when the scion and
rootstock are incompatible. In such cases, an interstock that is compatible with both
rootstock and scion is used. An interstock could increase the disease resistance or cold
hardiness of the scion. Plants also may be double worked to impart dwarfness or
influence flowering and fruiting of a scion.
Perpetuate clones. Clones of numerous species of conifers cannot be economically
reproduced from vegetative cuttings because the percentage of cuttings that root
successfully is low. Many can be grafted, however, onto seedling rootstocks. Colorado
blue spruce (Picea pungens, Engelm), Koster blue spruce (Picea pungens var.
Kosteriana, Henry), and Moerheim spruce (Picea pungens var. Moerheimii, Rujis) are
commonly grafted onto Norway spruce (Picea abies, Karst.) or Sitka spruce (Picea
sitchensis, Carr.) rootstock to perpetuate desirable clones. Numerous clones of Japanese
maple (Acer palmatum, Thunb.) that either root poorly or lack an extensive root system
are grafted onto seedling Acer palmatum rootstock.
Produce certain plant forms. Numerous horticultural plants owe their beauty to the fact
that they are grafted onto a standard, especially those that have a weeping or cascading
form. Examples include weeping hemlock (Tsuga canadensi.3, Carr. var. pendula,
Beissn.), which is grafted onto seedling hemlock rootstock (Tsuga canadensis, Carr.);
7. weeping flowering cherry (Prunus subhietella var. pendula, Tanaka), which is grafted
onto Mazzard cherry rootstock (Prunus avium, L.); and weeping dogwood (Cornus
florida, L. var. pendula, Dipp.), which is grafted onto flowering dogwood rootstock
(Cornus florida, L.). In most cases, multiple scions are grafted 3 feet or higher on the
main stem of the rootstock. When used this way, the rootstock is referred to as a standard.
It may require staking for several years until the standard is large enough to support the
cascading or weeping top.
Repair damaged plants. Large trees or specimen plants can be damaged easily at or
slightly above the soil line. The damage may be caused by maintenance equipment (such
as lawn mowers, trenchers, or construction equipment), or by disease, rodents, or winter
storms. The damage can often be repaired by planting several seedlings of the same
species around the injured tree and grafting them above the injury. This procedure is
referred to as inarching, approach grafting, or bridge grafting.
Increase the growth rate of seedlings. The seedling progeny of many fruit and nut
breeding programs, if left to develop naturally, may require 8 to 12 years to become
fruitful. However, if these progeny are grafted onto established plants, the time required
for them to flower and fruit is reduced dramatically. Another way to increase the growth
rate of seedlings is to graft more than one seedling onto a mature plant. Using this
procedure as a breeding tool saves time, space, and money.
Index viruses. Many plants carry viruses, although the symptoms may not always be
obvious or even visible. The presence or absence of the virus in the suspect plant can be
confirmed by grafting scions from the plant onto another plant that is highly susceptible
and will display prominent symptoms.
Simply the reasons for grafting usually are:
To perpetuate a variety.
To increase the ease and speed of multiplication.
To produce some radical change in the size, nature, habit, adaptation, or disease
resistance of rootstock or scion.
When to graft
Most grafting is done during winter and early spring while both scion and rootstock are
still dormant. Containerized plants may be moved indoors during the actual grafting
process; after grafting, these plants are placed in protected areas or in unheated
overwintering houses. Field-grown stock, of course, must be grafted in place. Some
deciduous trees are commonly grafted as bare rootstock during the winter and stored until
spring planting. Indoor winter grafting is often referred to as bench grafting because it is
accomplished at a bench.
How to graft
These are just general guidelines when collecting scion, each grafting technique may
have additional requirements of the scion.
8. 1. Timing. The best time of year to gather scionwood will vary with bio-regional climate
and type of fruit. The wood should be in the dormant stage and inspected for freeze
damage.
2. Authenticity. The best wood will be taken from healthy trees that have proven
themselves as productive and true to name and type. Label each variety carefully at
cutting time. Use a water proof label and marker.
3. Selection. For most types of dormant grafting, one-year old wood (last season's
growth) is generally considered best. Wood about a pencil diameter and 6 to 10 inches
long is usually ideal.
4. Storage. The essential requirements are to keep the wood moist and viable, but not so
wet as to rot, and maintaining a cool enough temperature to prevent premature bud-
swelling and protecting against freeze damage. Store scions in tightly sealed plastic bags
with some moisture in refrigeration until ready to use.
5. Disease. Be careful not to select scion wood from trees suspected of harboring
infestation of bacterial, viral, or fungal disease.
NOTE: In grafting the vascular cambium of the scion or bud must be aligned with the
vascular cambium of rootstock. In woody plants the cambium is a very thin ribbon of
actively dividing cells located just below the bark. The cambium produces conductive
tissue for the actively growing plant (Figure 1). This vascular cambium initiates callus
tissue at the graft and bud unions in addition to stimulating tissue growth on the basal
ends of many vegetative cuttings before they have rooted.
Cleft Graft
One of the simplest and most popular forms of grafting, cleft grafting (Figure 2), is a
method for top working both flowering and fruiting trees (apples, cherries, pears, and
peaches) in order to change varieties. Cleft grafting is also used to propagate varieties of
camellias that are difficult to root. This type of grafting is usually done during the winter
and early spring while both scion and rootstock are still dormant. Cleft grafting may be
performed on main stems or on lateral or scaffold branches.
The rootstock used for cleft grafting should range from 1 to 4 inches in diameter and
Figure 1 Cross section of a woody plant stem.
9. should be straight grained. The scion should be about 1
/4 inch in diameter, straight, and
long enough to have at least three buds. Scions that are between 6 and 8 inches long are
usually the easiest to use.
Figure 2. Cleft graft.
Preparing the Rootstock. The stock should be sawed off with a clean, smooth cut
perpendicular to the main axis of the stem to be grafted. Using a clefting tool wedge and
a mallet, make a split or "cleft" through the center of the stock and down 2 to 3 inches.
Remove the clefting tool wedge and drive the pick end of the tool into the center of the
newly made cleft so that the stock can be held open while inserting the scion.
Preparing the Scion. In cleft grafting, one scion is usually inserted at each end of the
cleft, so prepare two scions for each graft. Select scions that have three or four good
buds. Using a sharp, clean grafting knife, start near the base of the lowest bud and make
two opposing smooth-tapered cuts 1 to 2 inches long toward the basal end of the scion.
Cut the side with the lowest bud slightly thicker than the opposite side. Be sure the basal
end of the scion gradually tapers off along both sides.
Inserting the Scion. Insert a scion on each end of the cleft, with the wider side of the
wedge facing outward. The cambium of each scion should contact the cambium of the
rootstock.
Securing the Graft. Remove the clefting tool from the cleft so that the rootstock can
close. Pressure from the rootstock will hold the scions in place. Thoroughly seal all cut
surfaces with grafting wax or grafting paint to keep out water and prevent drying. If both
scions in the cleft "take," one will usually grow more rapidly than the other. After the
first growing season, choose the stronger scion and prune out the weaker.
NOTE: The temperature of grafting wax is critical. It must be hot enough to flow but
not so hot as to kill plant tissue. Recently, paint-like sealants have replaced wax in many
areas because they are easier to use and require no heating.
10. Side-Veneer Graft
At one time the side-veneer graft (Figure 3) was a popular technique for grafting
varieties of camellias and rhododendrons that are difficult to root. Currently, it is the most
popular way to graft conifers, especially those having a compact or dwarf form. Side-
veneer grafting is usually done on potted rootstock.
Figure 3. Side veneer graft
Preparing the Stock. Rootstock is grown in pots the season before grafting, allowed to
go dormant, and then stored as with other container nursery stock. After exposure to cold
weather for at least six weeks, the rootstock is brought into a cool greenhouse for a few
days before grafting takes place to encourage renewed root growth. The plant should not
be watered at this time.
Make a shallow downward cut about 3/4 inch to 1 inch long at the base of the stem on
the potted rootstock to expose a flap of bark with some wood still attached. Make an
inward cut at the base so that the flap of bark and wood can be removed from the
rootstock.
Preparing the Scion. Choose a scion with a diameter the same as or slightly smaller
than the rootstock. Make a sloping cut 3/4 to 1 inch long at the base of the scion.
Inserting the Scion. Insert the cut surface of the scion against the cut surface of the
rootstock. Be certain that the cambia contact each other.
Securing the Graft. Hold the scion in place using a rubber grafting strip, tape, or
grafting twine. Seal the entire graft area with warm grafting wax or grafting paint.
Remove the rubber or twine shortly after the union has healed. Never allow the binding
material to girdle the stem.
11. Whip and Tongue Graft
The whip and tongue technique (Figure 4) is most commonly used to graft nursery
crops or woody ornamentals. Both the rootstock and scion should be of equal size and
preferably no more than 1/2 inch in diameter. The technique is similar to splice grafting
except that the whip on the rootstock holds the tongue of the scion in place (and vice
versa). This leaves both hands free to wrap the joint.
For the whip and tongue graft, make similar cuts on both the stock and scion. These
cuts should be made with a single draw of the knife and should have a smooth surface so
that the two can develop a good graft union. Up to this point, rootstock and scion are cut
the same as for a splice graft.
Figure 4. Whip and tongue graft.
Preparing the Stock and Scion. Cut off the stock using a diagonal cut. The cut should
be four to five times longer than the diameter of the stock to be grafted. Make the same
kind of cut at the base of the scion.
Next, place the blade of the knife across the cut end of the stock, halfway between the
bark and pith (on the upper part of the cut surface). Use a single knife stroke to draw the
blade down at an angle through the wood and pith. Stop at the base of the initial diagonal
cut. This second cut must not follow the grain of the wood but should run parallel to the
first cut.
Inserting the Scion. Prepare the scion in the same way. Fit the scion into the rootstock
so that they interlock whip and tongue. Be certain that the cambia are aligned.
Securing the Graft. Wrap the junction with a grafting strip or twine, and seal it with
grafting wax or grafting paint. Never allow the binding material to girdle the stem.
12. Restoration use
Grafting techniques can be extremely useful in restoration work. Grafting can
substantially increase the speed of growth and multiplication among various woody
plants. Through the use of these techniques, a native plant production facility can quickly
grow several seedlings for restoration use. Grafting can also increase the hardiness and
disease resistance of trees, and other woody plants that may struggle in a particular area
or are just difficult to grow. If a tree is damaged during restoration work, grafting can
help rehabilitate and repair the damage to the tree.
Sources:
Hartmann, Hudsun T., Plant Propagation: Principles and Practices. Upper Saddle River:
Prentice Hall, 2002.
Kruckaberg, Artheur R., Gardening with Native Plants of the Pacific Northwest. Seattle:
University of Washington Press, 1996.
http://ag.arizona.edu/pubs/garden/mg/propagation/asexual.html
http://www.ces.ncsu.edu/depts/hort/hil/hil-8701.html
http://www.ces.ncsu.edu/depts/hort/hil/grafting.html
http://www.ces.ncsu.edu/depts/hort/hil/ag396.html
http://www.homeorchardsociety.org/article/3/
http://en.wikipedia.org/wiki/Grafting
By: Charlie Delius and Patrick Keegan