Clone the Garden
Most plants naturally reproduce from seeds.
Growing from seeds remains the most important way to propagate garden plants.
For example, all annuals and biennials have to be grown from seeds.
This includes flower plants, most vegetables and herbs.
|Four different seedlings from the same mother plant.
Pollination ensures that a mixture of genetic material from both parents is used to produce seeds.
The process is not perfect and often results in subtle variations and sometimes mutations.
In the wild variation, this keeps the population dynamic and versatile.
Seedlings with stronger traits survive better.
If the environment changes, chances are there will be seedlings with other traits that can better survive the changes.
In the garden however, this variation may be undesirable.
For example, if you plant a red rose, you want it to have red flowers, and not flowers with yellow stripes, or pink borders.
To ensure that propagated plants are true to their parents, asexual propagation (cloning) must be used.
A number of plants can be propagated using cuttings - usually a piece of branch stuck into a suitable medium.
The cutting grows roots where it touches the moist media, is then grown on as a new plant.
Sometimes leaves or roots are used as the cutting material.
Before the cutting has grown any roots, it needs to be kept from wilting.
Certain plants, especially succulents, store food and water, and have natural mechanisms to reduce the loss of water.
These plants can often last several weeks without water, and in that time will grow rots.
Other plants are more demanding of water, and will require a humid atmosphere to prevent wilting.
This is often provided by a humidity tent or propagator.
For the home gardener, a humidity tent can be simply made from a translucent plastic bag placed over the pot that holds the cuttings.
Use small bamboo skewers to keep the plastic away from the cuttings.
Sometimes, a rooting hormone is applied to the base of the cutting.
This will help difficult to root plants strike better, and faster.
Rooting hormone is not a magic bullet, and will only work if the conditions are right for the cutting to grow roots.
The hormone is also poisonous to plants, and should only be used in small quantities, and only on difficult to root plants.
Leaves grow from nodes along branches and it is this region that will also grow new roots.
When taking a cutting, it is important make the bottom cut just below a node.
With certain plants that have hollow wood, it is also beneficial to make the top cut just above a node.
The wood around nodes tend to be solid and this prevents water from collecting in the hollow centre.
There are three general types of cuttings, softwood (the growing tip), semi-hard and hardwood.
Softwood and semi-hard are primary used for those plants that root quickly, while hardwood cuttings can take many months.
Softwood cuttings are normally taken when the plant is actively growing, usually in Spring or Summer.
Lateral branches growing in good light make the best cuttings.
The cutting should have the growing tip, and be cut where the branch is still soft, but does not break easily when bent.
Strip out all but the top 2-3 leaves - and leave the growing tip on.
Large leaves should be cut in half.
The cuttings should be placed in moist sharp sand or pumice sand, several to a pot.
Alternatively, for small lots, use seed raising mix.
The pot should then be placed inside a humidity tent or propagator.
Site the tent or propagator somewhere bright, but out of direct sun.
Check every few days and remove any dead, fallen or diseased leaves.
Cuttings that have struck will start to grow.
For softwood cuttings, this should be in around 2-3 weeks.
Harden the cuttings over a few days by progressively opening the humidity tent.
Then gradually introduce them to more light.
Once hardened, they can be pricked out and grown on as small plants.
Examples of plants that will grow from softwood cuttings are fuchsia, begonia, arcotis and coleonema.
Semi-hardwood cuttings are made using wood that has just hardened but is still green.
As with softwood cuttings, remove all but the top 2-3 leaves.
They are usually larger than softwood, but are treated the same in the propagator.
Semi-hardwood cuttings tend to take longer to strike.
Examples of plants that will grow from semi-hardwood cuttings are camellia, certain connifers, hibiscus and rhododendron.
Hardwood cuttings of deciduous plants are usually taken in the winter, after the leaves have dropped.
The cuttings can be rather large, 30cm is common.
They are usually stuck into well drained soil and allowed to root over the winter.
Leave them to grow for a year, and dig up the following winter.
Examples of plants that will grow from hardwood cuttings are rose, grape, hydrangea and black current.
Heel, mallet, wounding cuttings
Plants naturally accumulate food and defences where a lateral joins a branch.
For hard to root plants, a heel or mallet cutting uses these reserves to aid rooting.
Sometimes a thick bark can stop roots from growing.
To work around this, the base of the cutting can be wounded, or a sliver of bark removed.
Certain plants will grow from pieces of leaves.
Long leaves are cut into lengths and struck just like softwood cuttings.
A new plant will then grow from the base of the leaf.
Examples of plants that can be propagated this way are cape primrose (Streptocarpus) and mother-in-law's tongue (Sansevaria).
The variegated mother-in-law's tongue can only be propagated by division as leaf propagated ones always grow to plants that do not have the variegation.
The veins on a large rex begonia's leaf can be cut and the whole leaf pinned down on a moist surface.
Little plants will grow where the veins are cut.
Alternatively, the leaf can be cut into pieces and each piece treated as a softwood cutting.
Cape violets can be propagated by using the whole leaf.
Shorten the leaf stalk to around 1.5 cm and treat like a softwood cutting.
A plant will grow from the base of the cut leaf.
Clematis can be
Sections of roots from certain plants can be used for propagation.
The roots are cut, cleaned, then treated like semi-hardwood cuttings.
Examples of plants that will grow from root cuttings are chrysanthemum, clematis, mint and raspberry.
Layering / stooling
A variation of the cutting technique is layering.
Instead of severing the branch from the mother plant, it is simply bent and pegged to the ground.
Sometimes the part of the branch that sits in the ground is wounded or girdled.
This enrourages roots to grow into the soil, and the branch can then be severed and grown on as a new plant.
Layering is useful for small quantities of plants without having to go through the trouble of using humidity tents, etc.
It obviously only works for plants where the branch can be easily bent down to the ground.
It is also useful for plants that do not strike well from cuttings, for example, whipcord and semi whipcord hebes.
Stooling / mounding is a variation on layering and can be used to propagate shrubs.
The shrub is first prunned hard.
Then when it regrows, soil is mounded onto the shrub, exposing only the tips of the new growth.
Soon the new growths will put down roots into the soil and can be detached and grown on as new plants.
Air layering, or marcotage, works best for plants where the branches cannot be bent down to the ground.
The branch is first wounded or girdled.
Then moist sphagnum moss is wrapped around it and a plastic bag wrapped around the moss keeps it in place and stops it from drying out.
The moss needs to be regularly checked and watered if it starts to dry out.
When the branch puts roots into the moss, it can be severed and grown on as a new plant.
Examples of plants that will grow from air layering are rubber tree (ficus), mango and witch hazel.
Division is probably the most straight forward way to propagate plants.
Any plant that grows in clumps can be divided.
In fact, regular divisions rejevenate these plants by reducing over crouding.
Herbaceous perennials that form multiple crowns can be dug up, divided and the divisions planted as new plants.
Each division should have one or more growing points or eyes.
For deciduous perennials, this is normally done when the leaves have dropped, but sometimes the eyes are not apparent until the plant starts to grow again.
In this case, it is better to divide just as growth is starting, but before any leaves unfurl.
Evergreen perennials are divided during their rest period or after flowering.
Tubers and rhizomes
Some perennials grow from tubers and rhizomes.
These can be propagated by separating the tubers and rhizomes, though one has to be careful as different plants have different growth pattern and this affects how they have to be split.
For example, bearded iris should be lifted every few years.
After flowering, lift the rhizomes and split them, keeping only the leading rhizome with a fan of leaves.
Trim the leaves back to half their length.
Then plant three rhizomes in a circle, with the direction of growth facing outwards.
Dahlia tubers are in fact swollen roots, and cannot grow shoots.
The crown contains all the growth eyes.
The tubers should be liften in autumn and stored in saw dust over the winter.
Around mid to late October, when the eyes will begin to swell.
Cut the crown into sections, taking care each section contains at least one eye and a medium sized tuber.
Bulbs and corms
Bulbs and corms normally grow offsets and after several years, a clump can become over crounded.
It is them best to lift these and replant the bulbs and corms.
A clump stat started out with half a dozen will often end up with several dozens.
The excess bulbs and corms can be planted in new clumps, or grown in pots for spring colour.
Large cymbidium plants can be divided.
Knock the plant out of its pot and shake loose as much as bark as possible.
Cut the roots from the bottom of the root ball and work your way to the centre of the plant.
Usually, there will be weak spots where the plant has naturally divided.
Divide the plant along these weak spots, taking care not to break any fragile new growths.
Remove all back bulbs (bulbs with no leaves) from the centre.
Each division should have a few front bulbs (bulbs with leaves).
The individual back bulbs can be left in a cool bright spot to sprout.
Allow the sprouts to grow leaves and roots and pot the bulb as a new plant.
After a year or so, the back bulb will have shrivelled and should then be removed from the young plant.
Plants that should not be divided
Certain plants should not be divided.
If the tuber of a begonia is cut, the cut surfaces will heal but will not grow roots.
Tuberous begonias are usually propagated via softwood cuttings or tissue cultured.
Similarly cyclamen tubers should also not be cut.
The cut does not heal proparly, often resulting in the death of the plant.
Cyclamens are usually grown from seed.
The scales of a lily bulb can be detached and placed in a humid environment.
A small bulb will form at the base of each scale.
Tunicate bulbs, for example, daffodils, can be cut into sections, each with a part of the basal plate.
The sections are further divided into pieces that contain two scales.
When placed in a humid and warm environment, each piece will grow a small bulb.
The alternative method is to remove the basal plate completely.
Several cuts are then made into the bottom of the bulb.
The bulb is then planted up side down in moist madia.
Small bulbs will grow where the cuts are made.
Grafting and Budding
Grafting and budding is a process where a piece of a plant (the scion) is attached to another (root stock).
The scion binds with root stock and then grows the branches and leaves of the plant.
The root stock grows the roots.
Different root stocks can be used to impart cold hardiness, to dwarf the plant (eg. apples), and even, to increase the vigour of the plant (eg. tomatoes).
There are several grafting and budding techniques and these will be covered in a future article.
Kei kei's and Plantlets
Certain plants grow kei kei's (Hawaiian word for babies) or plantlets along their branches, bulbs and even leaves.
A number of kalanchoe species grow plantlets along the margins of their leaves.
These easily detach and will then grow into a new plant each.
The hen and chicken fern (Asplenium bulbiferum) grows plantlets at the ends of its fronds.
The spider plant (Chlorophytum comosum) grows plantlets on its flower spikes, and piggyback plant (Tolmiea menziesii) grows a plantlet where the leaf joins the stalk.
Strawberry grows plantlets at the ends of long runners.
Certain orchids grow plantlets either at the end of their pseudobulbs, or along long canes.
When these plantlets are large enough and have started to grow their own roots, they can be detached from the mother plant and grown on as new plants.
Orchid kei kei
Certain varieties of lilies grow bulblets along their stem.
When the stem dies, these bulblets can be detached and grown on as new plants.
It normally takes aound three years for these new plants to flower.
A method of propagation developed for the laboratory is meristem or tissue culture.
The growing tip (meristem) of the plant is removed from the plant and grown in flasks that contain sterile agar and small quantities of food.
The meristem eventually grows into a callus of cells.
This is then cut up and grown on.
Eventually, thousands of plants can be propagated from one meristem.
This method of propagation does have its disadvantages.
Prolonged growth of meristem cells in the laboratory can induce genetic mutations.
These mutations can result in weak plants, or plants that do not grow as expected.
For example, tissue cultured Aloe polyphylla sometimes do not grow into the spiral pattern, and cabbage trees sometimes do not form trunks.