Propagation Of Begonias
In plants in the natural world, the act of reproduction is through the transfer of pollen from the
stamens of the male flower to the pistils of the female, either by wind or insects. This results in the
fertilization of the female ovaries and eventually the formation of seed. When ripe, the seedpod splits,
allowing the seed to disperse, some of which germinates, thus perpetuating the species.
In the world of horticulture, the natural process can be controlled by using selected plants to obtain
seed, which is known as hybridization. In addition, various methods of taking
and rooting vegetative cutting material to increase stock are available.
Begonias from seed
If the seedlings are to flower in the following summer, the seed must be sown in mid-winter;
therefore, it is necessary to have both bottom heat and light. You can, however, raise begonias from
seed sown later in the winter or early in the spring, when a warm situation will promote germination
just as well. Although there is little chance of seeing flowers that year, the plants will produce tubers by
winter, which may be grown the following season. Regardless of timing, the advice is essentially the same.
- The main key to successful seed-raising is hygiene. The trays should be sterilized before use with a
bleach solution. Using the bleach at the rate of one part bleach to ten parts of clean, cold water, soak
the equipment for 10 to 15 minutes, and leave it to drain and dry before use.
The mix required for successful germination of begonia seeds should be fine and
have little or no added fertilizer.
Regardless of the size of the seed tray, the depth of the mix need not be great. A layer of previously
sterilized, coarser material (either pumice, sand or coarse potting mix) about 1.5 in (4 cm) deep placed
in the bottom of the tray will assist with drainage. The damp, sterilized, seed-raising mix is then spread
over this to a depth of 1 in (2-3 cm) and pressed down lightly with a block of wood to make a flat surface.
Then set the tray in a container of water. To further prevent infection by mold or fungi, use water
that is either distilled or previously boiled and cooled, with a small amount of antifungal spray
added (mixed according to instructions on the container). Allow the tray to draw up moisture until
the surface of the mix is thoroughly damp, then leave it to drain.
- Sowing the seed
- Now sprinkle the seed evenly over the surface. Begonia seed is exceptionally fine, so the addition
of a teaspoon (5 ml) of very fine sand or, failing that, powder
sugar to the seed will show exactly
where it is falling in the tray, thus ensuring an even spread.
Immediately after sowing, mist the surface using the above antifungal solution
so that the seed is wet. Do not overdo this, or the tiny seed may float and fall
into the spaces at the edges.
Cover the tray with a sheet of clear glass or place it inside a plastic bag. Then, if it is winter, place it
on the source of bottom heat with the thermostat set to keep the mix at a constant 70°F (21°C).
If the seed is sown in springtime when bottom heat is not needed, place the tray in a warm
location, though not in direct sunlight, where it will have a temperature range between 65-71°F (18-22°C).
- Germination normally occurs in seven to ten days. Keep the seed damp during this period with misting
every four to five days. Turn the glass over each day to keep large drops of condensation from swamping
the tiny seed and, later on, the seedlings. If no germination is noticed after 14 days, try a fraction
more heat, but no more than 75°F (24°C) or the seed will cook. Germination will be slower when
the seed is planted in spring with no bottom heat and some species seed may take 21 days or longer to germinate.
The tiny seedlings are very susceptible to drafts, so keep the glass or plastic on until the first two
leaves show. Then the cover can be moved, allowing a small gap of about 1/2 in (1 cm) to give some
ventilation. When the third leaf (the first true leaf) is about 1/2 in (1 cm) in diameter, the glass can be
removed. The seedlings should then be misted daily. Each week, foliar feed with a high-phosphate
fertilizer at one-quarter strength to help encourage root growth.
- Damping off
- Damping off is a fungal problem that can occur with small seedlings, causing them to wilt and die. With
a sterilized mix, the nasty pathogens that cause such outbreaks should have all been killed off. As the
seedlings start to mature, some ventilation will help prevent damping off.
Sometimes a gray or green mold appears on the surface of the mix. In this case, try increasing the
strength of the spray mixtures, and consider also pricking out the seedlings to a new, clean mix,
providing they are large enough when the problem occurs.
- As a rule of thumb, the seedlings can be safely transplanted or pricked out at any time following the
appearance of the first true leaf; the actual timing comes down to personal preference. However, if the
tray is crowded, a move is often beneficial much sooner than this. If not, they can be left to grow a
little bigger. Continue feeding with one-quarter strength high-phosphate fertilizer.
- Sources of seed
- Widely available from seed merchants are Semperflorens, Non-stops, and some types of Large-flowered
tuberous begonias, e.g., those known as the Memory strain (a group of similar
type and mixed colors, but not to be confused with individually named begonias), frilled Fimbriata types (Carnation begonias),
and unnamed Pendulas or basket begonias. Seed for many species begonias and
species hybrids is often available only through societies and special interest
groups, many of whom run seed banks for interested growers.
The following describes vegetative reproduction methods used for tuberous begonias.
- Tuber division
- Some people cut their tubers up because they
think they have grown too large, or that such a method will rejuvenate the tuber.
In fact, the cut tuber sections are still the same age as the old tuber, so the
idea of rejuvenation is a fallacy. If a large, old tuber is cut in half, you
will then have two old tubers. Furthermore, since roots will not grow on any cut tuber surface, the plants derived from this method are likely to be somewhat
inferior due to a reduced capacity to take up nutrients. A plant’s root system is like the engine of a
car-the larger it is, the more power it develops; likewise, the larger the root system, the better the
plant that will grow, giving bigger flowers. In addition, there is the increased likelihood of disease
affecting the cut surfaces. So this is not a method to be recommended unless as a desperate last resort.
However, tubers can occasionally be divided. Basket varieties sometimes form a
little chain of small tubers joined by a narrow stem. These can be broken off and grown separately. In
addition, some upright varieties have tubers that look like a figure eight-in fact, two tubers joined
just by a small neck. These can simply be broken off and the resulting small wound dusted with
after trimming. In these instances, there really are two for the price of one.
- Propagation by cuttings
- The only way to obtain new, vigorous stock is by taking cuttings, which will lead to the production of
new, healthy, vigorous tubers. The plants from cuttings should not be allowed to flower in the first
season. Remove any flower buds and the growing tip when the plant is 8-10 in (20-25 cm) tall, thus
making sure the growth goes into forming a tuber.
The best form of cutting material, and the most successful, are basal shoots. As the
tubers start into growth in spring, they will often show many buds. Not all of these will necessarily
produce shoots, nevertheless, there are usually an excess number of shoots relative to the number of
stems desirable on the plant. These shoots can be removed as basal cuttings when they are 3-4 in
(7.5-10 cm) in height.
There are two methods of taking basal cuttings, and both are easier if timed to coincide with
repotting. The first is to clean away some potting mix from the base of the selected
shoot, then gently grasp it between finger and thumb close to its base, and rock it to and fro. After
a few waggles, the shoot will break away from the tuber. This can be repeated according to the
number to be removed.
On all cuttings there will be bracts that protect the dormant buds. Removing these at this point will
reduce the chance of their rotting and transferring this rot to the cutting itself. If the tuber has been
well-covered with mix, there are also often roots already formed at the base of the cutting, which will
give it a head start in life. Place the cutting in a
small, clean container and label immediately, giving details of name and the date taken. The wound(s)
on the tuber should then be dusted with sulfur or some other fungicide powder.
Do not dust the cutting itself.
The cutting does not have to be potted up or placed in a propagator immediately. If left for 30 to
60 minutes, the wound at the base of the stem will dry and begin to form a callus over the wound.
The alternative, and probably the most popular, method of removal of the basal shoots is to use a
knife or scalpel. This should be cleaned before use by dipping it in methylated spirits, then dried with
a tissue. At the base of a basal shoot is an eye or embryonic bud. The cut should be made
immediately below this eye, which has to be present for the eventual tuber to start into growth the following spring.
The surface of the tuber will have many dormant buds that will form shoots in the years to come.
Care should be taken to avoid slicing away part of the tuber when cutting off a basal shoot, for this will
destroy some of these buds and impair the productivity of the tuber in future years.
Once the cutting is removed, treat the wound on the tuber as mentioned above. Do not replace the
potting mix over the wound, and do not water until the wound on the tuber has dried properly, usually about two days.
Stem cuttings, which are obtained by removing a side shoot from the main stem of the plant, are the
next best type of cutting. The first four leaves on the main stem will usually develop side shoots. Above
this on the stalk, the buds are usually flower buds that are of no use as cuttings. It is usual to leave two
side shoots to develop fully, to give a really full complement of flowers on the plant. However, if cutting
material is in short supply for a particular variety, then the use of these shoots becomes necessary. Not
all begonia varieties give these shoots in any quantity. Removing them can at times be difficult
because of the restriction of space.
The shoots are removed with a sterile scalpel or small knife by making two cuts, one vertically
downward parallel to the main stem, the other below the cutting, sliding the blade along the leaf
stem, ensuring that the eye is taken with the cutting. These cuts will result in a wedge shape at the
base of the cutting.
An alternative method is to make the cut straight across on the side shoot, just below the first
leaf axil, where an eye will generally be found. The remaining stump of side-shoot stem should be
trimmed back to about 1/2 in (1 cm), dusted and allowed to drop naturally, which it will do after a
few days. There is, of course, still an eye at the base of this stump, which will develop into another side
shoot. This could provide a second cutting or be left to grow and flower in due course, but it would be
extremely late in doing so.
After treating the wound on the stem, label the cutting by
recording the name of the variety and the date on a plastic label.
- Leaves with a dormant bud
- Use can be made of any leaves coming directly from the main stem that have a small eye or bud nestled
in the axil with the main stem. These are not true leaf cuttings, for, if left, they will
develop into side shoots. Using a sterilized instrument, take a very thin slice of the actual main stem
and remove the leaf with the eye intact. Treat as for a stem cutting; remember to dust the wound on the stem of the plant.
- Methods of rooting cuttings
- Two types of hormone are designed to promote root development on the
market; one is a powder and the other a gel. The latter has the advantage of sealing off the whole base
of the shoot. A similar rationale is behind another idea, that of dipping the lower 1 in (2.5 cm) of the
stem of the cutting in honey. This seals the stem from harmful pathogens, thus preventing fungal infection,
and is also said to help promote root growth.
Using a misting unit
The most effective way to root cuttings is to use a misting unit.
Cuttings are effectively small plants, though initially without a root system. In order to survive, all
plants, large and small, transpire through their leaves the moisture normally taken up by their
roots. Cuttings, because they lack roots, cannot replace this moisture. For this reason, they (and
newly transplanted seedlings) will wilt. The high humidity in a misting unit helps keep the cuttings
turgid until the formation of roots allows moisture to be taken up.
The success of such a unit relies on the temperature differential between the base and the foliage
of the cuttings. The mist helps keep the foliage cool, and the constant spray prevents fungi or bacteria
spores getting a foothold and causing disease, while the warmth below encourages the formation of
roots. With such a unit there is no need for a covering of any type, and cuttings will be well-rooted in
three to four weeks, when they can be potted up into normal potting mix.
Rooting without a mister
Without a mister, and with care, it is still possible to increase stock or to renew an aging tuber by growing a cutting.
Fill a container about 5 in (12 cm) in diameter with some normal potting mix. Using a spoon,
remove the mix from the center of the container to a depth of 2 in (5 cm) and replace it with pumice or
sand. Water the mix well, then make a hole with your finger in the center of the pumice/sand and
insert the cutting into it. Press the pumice around the stem of the cutting so it is well supported. This
method will allow both good drainage and air porosity, essential for good root growth.
Now make a simple propagator by cutting the bottom from a clear plastic soft-drink bottle that is
large enough to fit snugly inside the rim of the container when placed over the cutting. If the cutting
is large, it may be necessary to trim the leaves by up to a third so they do not touch the inside of the
bottle; otherwise, the leaves will rot.
Alternatively, use a clean, clear, plastic bag large enough to envelop the whole container. A thick
wire in the shape of a hoop placed in the container will support the bag and help prevent the foliage
from touching the inside of the bag.
Now leave the container undisturbed in a well-lit place out of direct sunlight for three to four
weeks. After this time, the bottle or bag can be removed and the cutting treated as an individual
plant. There will be no need to repot the cutting, as roots, which have developed in the pumice, will
grow through and into the mix.
Small, cheap plastic propagators, which are available in various sizes from most
nurseries, can also be used.
Using sphagnum moss
Another simple method of rooting cuttings is to use sphagnum moss. This can be either milled into fine
particles or roughly chopped, or even used as is. It is best to cut it up so that the cutting can be easily
removed without damaging the roots. Place the moss in a 5-6 in (12-15 cm) container and water,
soaking it well. Using a finger, make holes in the moss close to the edge of the container and insert a
cutting into each hole, gently pressing the moss around the base of the cutting. When the container
is full, place it in a well-lit spot out of direct sunlight and leave for three to four weeks, watering the moss
should it begin to dry out. After this time, the cuttings will be well-rooted and can be potted into
potting mix. There is no need to use a mister or cover with a bottle, as the moist moss supplies enough
humidity around the cuttings for them to remain turgid.
Rooting in water
Cuttings that have a stem will root quite well in water, and some growers use only this method.
Select a container that is a suitable length for the cutting-small jars are ideal, as are
orchid phials or
clear plastic film containers. Make sure the container is sterile and preferably use distilled or
previously boiled water. Put about 1/2 to 1 in (1-2 cm) of water in the bottom of the container, then place the
cutting into this and allow it to lean against the side. Place in a well-lit location but out of direct
sunlight. Roots should appear in approximately four to five weeks. Roots formed in water tend to be
somewhat more delicate than other roots, so allow them to grow only to 1/2 in (1 cm) long before
potting the cutting, and take special care to avoid damaging them.
Whichever method is used to grow the cuttings, remember that some form of bottom
heat will speed up the rooting time. You can place about 6 in (15 cm) of moist horse or other
animal manure in the base of a deep box and covering it with a layer of plastic. The cutting containers
then simply sit on the plastic. The gentle heat generated by the manure is as effective
as a heat pad in speeding up the rooting time.
- Leaf cuttings
- Until recently, it was always thought that, unlike leaves taken from Rex or other rhizomatous
begonias, leaf cuttings from Large-flowered tuberous begonias did not produce viable tubers. However,
this has now been disproved. Although slower and somewhat more difficult than using basal or stem
cuttings, this method can be very useful for increasing stock of rare or otherwise difficult varieties. It is
particularly useful with Pendula varieties, where it is desirable to retain all the initial shoots to give a
greater profusion of flowers.
The method of removal is very simple. Again, use a sterilized instrument and make a clean,
straight cut through the leaf stem. It does not matter where this cut is made. New leaves from the
lower third of the plant seem to produce better results.
Rooting leaf cuttings
A slightly different approach is required in rooting leaf cuttings. It is better not to insert the leaf stem
into the rooting medium but merely hold it firmly against the medium. To do this, pierce the leaf with
a fine skewer or kebab stick, preferably one that has been sterilized, and push the skewer down into the
pumice or sand so the leaf is supported with the stem’s cut surface resting on the medium. After
about ten days, a swelling and callus will form at the end of the stem, and eventually roots appear.
Following this, individual shoots, sometimes as many as ten, will form around the swelling. These shoots
will form individual plantlets. At this stage, the entire growing leaf plus plantlets may be potted, or
alternatively, the individual plantlets may be left until large enough and potted separately.
The main drawback with this method of securing the leaf is that rot often sets in around the
wound caused by the skewer. To overcome this, holes can be made in the selected leaves about a
week in advance of their removal from the plant. This then allows the wound to heal and callus
before the cutting is taken. A moist environment is essential to keep damp the medium in contact with
the cut surface. Again, a mister is the ideal, but the soft-drink bottle method is also successful.