The Next Generation
The seed is the primary way that higher plants employ for reproduction.
A seed is a remarkable piece of engineering.
It contains a dormant plant embryo, and food and nutrients, all packaged dry within a protective skin.
When the conditions are right, the seeds absorbs water and the embryo grows into a seedling, fed by the seed's food reserves.
In the garden, all annuals, biennials, vegetables, herbs, and certain trees and shrubs are raised from seed.
Plant breeders also raise new varieties from seed.
For a small outlay in money and time, a beautiful garden of annuals and flowering perennials can be easily created.
The veggie garden can be filled from plants grown from seed.
All it takes is a bit of patience and the know how:
Seeds require water, air and warmth to germinate.
Water usually triggers germination - the embryo soaks up water, wakes up from dormancy and starts to grow.
All that the seed needs to grow is already packaged within the seed, so there is no need to feed the seed.
As it grows, it also needs to breathe.
The germination medium should be moist, but also free draining.
There needs to be small gaps that allow air to freely pass through to the seed.
A commercial seed raising mix is usually suitable.
They are inexpensive and as only a small amount is used, a small bag goes a long way.
Water the seed raising mix and allow it to drain before sowing.
Then top up with more seed raising mix to bury the seeds to the correct depth, then mist the top to thoroughly wet it.
Do not bury the seeds too deep.
Deep burial means less air gets to the seed, and when the seed germinates, the tiny emerging seedling has to push through a thick layer of seed raising mix.
As a general rule, seeds should only be buried up to twice their size.
Tiny seeds should only be sprinkled on the surface and then misted.
Certain seeds such as pumpkins and beans are usually sown in-situ.
Prepare the soil first, and then dig a small hole for the seed.
Sow the seed and top up with seed raising mix.
Water in well.
Plants grow in variety of climates, ranging from the warm humid tropical forests to cold and drier temperates.
Different plants therefore tolerate and prefer different ranges of temperatures.
It should then be expected that their seeds also require different temperatures.
Most tropical plant seeds will only germinate in very warm conditions, say above 20°C.
Plants from cooler temperate regions still require a bit of warmth but will germinate in much cooler temperatures, 12-15°C.
Seeds will often germinate within a range of temperatures, but when the temperature is at the optimum, the rate of germination is at its best, and germination the fastest.
A cold frame can be used to start seeds.
Fill up a container with seed raising mix, wet and sow the seeds.
A light misting on the surface helps settle the seeds.
Place the container into the cold frame.
Seeds of warmer plants can be started in the greenhouse or indoors.
Place the container into a translucent plastic bag to create a humidity tent.
Alternatively, the hot water cupboard can be used - the seeds will need to be checked regularly, and often, and seedlings removed as soon as germination is apparent.
When sowing directly into the ground, make sure the soil is warm enough.
Cold wet soil often kills seeds.
For beans in the veggie garden, November is the earliest that they should be started.
Certain seeds require darkness to germinate.
Place a thick layer of newspapers over the glass to keep the light out.
When the seeds have germinated, the newspaper can be removed.
Do not leave the seedlings for too long under the newspaper or they will become too lanky and weakened.
There is another group of seeds that require light to germinate.
These should always be sown on the surface of the seed raising mix and never covered.
DO NOT place the seeds in full sun though, as only a small amount of light required for germination.
The full sun will most certainly kill the seeds.
Seeds absorb water initially through the seed coat.
This is usually sufficient to soften and break the seed coat, allowing the seed to absorb even more water.
Some seeds have watertight seed coats.
For the seed to germinate, the tough seed coat must be first broken down, a process known as scarification.
There are several techniques.
Seeds from the hibiscus family will germinate better if hot (not boiling) water is poured over the seeds.
Allow the seeds to soak for a few minutes then drain.
Soak the seeds in tepid water overnight.
Sow those seeds that have swollen and repeat the treatment for those that haven't.
The other method is to line the lid of a bottle with sand paper.
Place a few seeds in the bottle and cover with the lid.
Vigorously shake the seeds and then soak.
Repeat for those that did not swell.
Kowhai seeds can be nicked with a knife and soaked overnight between layers of damp paper towels.
The next day, gently peel off the leathery seed coat and plant the seeds immediately.
The yellow dye that stains the paper comes from the seed coat, and contains a chemical that inhibits germination.
By soaking and then peeling away the seed coat, this inhibitor is leached away, allowing the seed to germinate.
For more information, please see kowhai germination notes.
Plants that grow in colder climates usually shed seeds either in late summer or in the autumn.
If these seeds were to germinate in autumn, the winter will kill the seedlings.
So to ensure the survival of the seedlings, the seeds contain germination inhibitors that are broken down only by the cold.
Aquilegia seeds require a
cold period to germinate.
These seeds should be started outdoors in the autumn.
Allow the seeds to experience the cold winter, but try to avoid getting them frozen.
Germination will begin when the warmer weather arrives in the spring.
This practise is know as stratification - because nurseries used to stack layers of seeds outdoors to germinate.
Alternatively, sow the seeds in a pot of moist seed raising mix, place the pot inside a plastic bag and store in the fridge (not freezer).
Check weekly and remove from the fridge as soon as you see any signs of germination.
Different seeds require different length of time, but for most, the pot should be removed after a month and the seed allowed to germinate normally.
Sometimes a combination of both scarification and stratification is needed for germination.
Care for seedlings
Seeds are started in a controlled environment where with high humidity, warmth and low light.
If seedlings are removed from the environment, they may be stressed and will be weakened or may even die.
They need to be gradually acclimatised to their new environment.
For example, if the pot is in a plastic bag, do not open it immediately.
Instead, open a small amount every day, gradually, over a few days, remove the bag.
This allows the seedling time to toughen for the new environment.
Seedlings have small root systems that are prone to drying out.
Water them more frequently, and regularly.
Feed with applications of weak liquid fertiliser, preferbly at every watering.
The fertiliser strength can be gradually increased as the plant grows bigger.
Seedlings should also be initially grown in a semi-sunny spot.
As they grow bigger, gradually move them to full sun.
In the wild, most seeds germinate in the shade of larger plants and the seedlings spend the first part of the lives shaded.
They only get the full sun after that have outgrown their neighbours.
The most common disease that afflicts seedlings is damping off.
It is caused by a number of fungi species.
The symptom is a rapid collapse of seedlings.
Sometimes the disease can strike even before seedlings emerge, making it seem as if the seeds are not viable.
Hygiene is the best prevention for this disease.
Sterilise all pots and tools by washing off all soil and then soak in a 10% bleach solution for an hour.
Do not reuse old seed raising mix.
Begin the acclimatisation process as soon as seedlings emerge.
Humid environments increases the risk of fungal diseases.
Good quality seed raising mix is usually weed free, and if the seeds are started under cover, it is unlikely that weeds will germinate and compete against the seedlings.
However, seeds sown in-situ will have to face competition from weeds from day one.
Careful weeding may be necessary to prevent the weeds from crouding out the seedling.
Correct identification of seedlings is important, if one does not want to accidently pull them out when weeding.
Spaghetti melon seedling showing two expanded
cotyledons and one true leaf.
In general, there are two types of germination.
In a hypocotyl germination, the top of the root (hypocotyl) pushes the seed out of the ground and the cotyledons (seed leaves) expand to become the seedling's first leaves.
Often these look very dissimilar to the plant normal leaves.
In epicotyl germination, the seed remains burried, but the stem (epicotyl) above the cotyledons grows and pushes itself out of the ground.
It then unfurls the plants first leaves, which are its true leaves.
Hippeastrum and a number of other bulbs produce seeds that are thin and papery.
The float method can be used to pre-sprout these seeds.
Fill a plastic container (such as a old margarine tub) with 3 cm of water.
Carefully place the seeds on the surface of the water, making sure they float.
Top up the water if required, taking care not to sink any seeds.
Sunken seeds that no longer float should be removed and sown immediately.
After some weeks, the seeds will start to grow a root.
Remove these and plant so that the seed is on the surface and the root in the seed raising mix.
Orchid seedlings inside
a sterile flask
Orchids are an odity in the seed bearing plant family.
Their seeds are microscopic, easilly carried away even by the gentlest of breezes.
They are so tiny that they do not contain any stored food.
For the seed to germinate, it needs to be first infected by fungus.
The fungus feeds the seed allowing it to germinate.
Each orchid species has its own fungus species.
Once the seed has germinated, it no longer requires the fungus and the relationship ends there.
Certain orhid species however, carry this relationship further, and in fact parasitise on the fungus.
These often live underground, have no leaves or any chlorophyl.
Only the flowers appear above ground, and in certain species, by not much!
Orchid seeds are normally grown in sterile flasks.
These flasks contain agar and a mixture of nutrients and sugars.
The seeds are sown on the agar, and fed by the nutrients, will germinate.