The first step in growing orchids from seed is the one that requires the most careful planning. Your choice of parent plants will determine the success of your cross. Your parent orchid plants should have all your desired characteristics such as:
- Vigorous plant & root growth, disease resistance.
- Good flower shape, size, colour & number of flowers.
- Flower habit, do they stand upright?
- Plant growth habit, compact or straggly?
- Cold and heat tolerance.
Selfings will produce plants which resemble the parent plants more closely than sibling crosses, but selfings tend to produce weaker plants.
Pollination is the process of transferring pollen from one flower to another. Orchids do not have powdery pollen like most other flowering plants. Their pollen grains are compacted into structures called pollen masses, which are about the size of a grain of wheat. Instead of transferring the pollen from one flower to another with a brush as with other plants, orchid pollen is removed with a toothpick because of the pollen structure.
The pollen masses are located behind the pollen cap at the front part of the flower. The cap must be hinged out of the way or removed to gain access to the pollen masses. The pollen masses are then transferred to the stigmatic area of another flower, a sticky depression further back in the flower. See the photograph below to see where the pollen cap and stigmatic area are located.
Pollination tends to be more successful using fresh flowers when they are receptive. A good sign that a flower is receptive is when it is fragrant. Make sure that you record all the information about the pollination in a notebook and tag the pollinated flower. It is a good idea to make a reverse cross because one plant may be a better capsule parent than the other.
If you want to make a cross of two orchids which flower at different times of the year, you can store pollen from one flower for later use with a flower of another plant. The pollen will last for several months if stored in the fridge at about 4°C and kept dry by storing with a moisture absorbing chemical such as silica gel.
When you come to use the stored pollen it will be quite dry and must first be allowed to absorb some moisture. Place the dry pollen masses onto a glass plate or similar surface, just touching a drop of water and leave it for an hour. The pollen masses will swell and be ready to use.
Once the pollen masses come into contact with the stigmatic area of the recipient flower, the pollen grains which make up the pollen mass, will be stimulated to germinate by chemicals on the sticky stigmatic area. Each pollen grain will produce a pollen tube and this mass of tubes from all the thousands of pollen grains will grow down into the flower until they reach the ovary behind the flower. When the pollen tubes reach the ovary fertilization takes place and hopefully, each one will produce an orchid seed. After a few days the pollinated flower will fade. This fading is in response to the removal of the pollen masses or pollination and does not yet indicate successful pollination.
Over the following weeks or months, as the seed forms, the ovary develops to become a seed capsule and will gradually mature.
Initially the pod will be dark green and quite hard with a thick wall and little inside it. As the embryos grow inside the capsule the wall will become thinner and the seed will occupy more space, causing the capsule to swell like a balloon until maturity. During this time the pod usually changes colour to yellow / green and 3 ribs form. While the capsule is maturing protect the plant from temperature extremes, rain, excess humidity, direct sun and insects. Temperature extremes may cause pods to drop, excess humidity may result in fungal damage, insects hollow out capsules and sun can cause premature splitting.
The table below gives a very rough indication as to when a capsule is mature. It is a very rough indication because the time taken for the capsule to mature varies greatly not only depending on the genus of the orchid but also on the time of the year, climatic zone, temperature and light intensity. The process takes from a few weeks for Disas up to 18 months for some Paphiopedilums. When the capsule reaches maturity it cracks and releases dry seed.
HARVEST TIMES FOR CAPSULES OF SOME ORCHID GENERA
Genus Range of Harvest Times( days )
- Aerides150 – 180
- Epidendrum100 – 120
- Ansellia120 – 180
- Laelia120 – 180
- Ascocentrum110 – 180
- Masdevallia80 – 90
- Brassovola120 – 150
- Maxillaria120 – 140
- Bulbophyllum140 – 180
- Miltonia130 – 150
- labiate130 – 180
- bifoliate200 – 250
- Odontoglossum210 – 270
- Oncidium70 – 240
- Paphiopedilum180 – 440
- Cirrhopetalum140 – 180
- Phaius120 – 150
- Cymbidium270 – 350
- Phalaenopsis200 – 220
- nobile150 – 180
- phalaenopsis120 – 140
- Australian species60 – 150
- Pleione150 – 180
- Sarcochilus300 – 360
- Sophronitis75 – 100
- Disa35 – 45
- Vanda150 – 195
- Encyclia210 – 250
- Vandopsis160 – 180
INTACT PODS OR DRY SEED?
There are advantages and disadvantages with both ways of collecting orchid seed.
Intact seed capsules eliminate the need for directly sterilizing the seed when sowing, which generally results in more viable seed and faster germination of seed. However if intact seed capsules are harvested too early the seed may be immature resulting in no germination at all or very poor germination. Dry seed must be treated with strong disinfectants to kill fungi and bacteria and this frequently destroys a portion of the seed. Orchid seed matures gradually along the length of a pod, therefore harvesting a little too early may result in only half the seed being mature. There are some other reasons for choosing dry seed or intact capsules for specific genera. Many Odontoglossums are infected with viruses and the scraping of the seed capsules during the sowing of intact pods almost always transfers the viruses to the seedlings. Dry seed has a much lower chance of passing on viruses and so can achieve virus free seedlings from an infected parent plant. Some Disa seed starts to germinate while still inside the intact pod. This seed will be destroyed during the dry seed disinfection process, therefore only intact capsules are recommended for Disas. The dry seed disinfection process actually breaks the tough seed coat of some Paphiopedilums, greatly improving germination. The reverse is the case for other Paphiopedilums.
ESTIMATING WHEN INTACT CAPSULES ARE READY
Probably the best way to determine when to harvest orchid seed capsules is by looking for changes in their visual appearance. The best time is just before they are due to split.
The best indications that the capsule is ready to harvest are the pod has swollen, the colour has changed and the three ribs joining the segments have started to lift. Shine a strong light on the capsule from behind and look at the seed through the capsule. As the seed gets closer to maturity you can see a colour change in many genera from white to various colours. Once the seed is coloured it is generally mature. See some genus specific notes below. If you are unsure whether a capsule is mature it is best to wait and collect dry seed. Harvesting capsules too early results in immature seed or low germination numbers.
SEED & CAPSULE APPEARANCE WHEN SEEDS ARE MATURE
|Genus||Capsule Size||Capsule Swelling||Capsule Colour||Seed Colour|
|Cattleya||Large||Little||Green||White to cream|
|Dendrobium – Aust.||Medium||Much||Yellow/green||Golden|
|Laelia||Small-Medium||Moderate||Green||White to cream|
|Oncidium||Small-medium||Much||Pale green||Cream to yellow|
|Phalaenopsis||Medium-large||Little||Dark green/brown||Dark brown|
|Pleione||Small||Moderate||Pale green||Tan #|
* Seed still germinates when a little immature and cream coloured.
# Often mixed with infertile white seed.
THE REASONS WHY SOME POLLINATIONS MAY FAIL
Many orchids are self incompatible. Orchids have different chromosome numbers and mismatched numbers often leads to non-viable seed or sterile seedlings eg triploids. This is particularly a problem with complex Sarcochilus, Odontoglossum and Masdevallia Hybrids. Pods may turn bright yellow and drop off at 2/3 maturity or just be hollow.
AFTER COLLECTING SEED
Place intact pods or dry seed in a paper envelope, NOT PLASTIC as this may sweat and result in fungal damage to the seed. Seal envelope edges with tape because orchid seed is very fine and may leak out. Pack in a rigid container before mailing to an orchid flasking laboratory.
Orchid seed is different to that of almost all other plants because it has virtually no food supply. In most plants what we see as the seed is actually about 95% food supply to nourish the developing plant for the first few weeks of life. This is why orchid seed is so fine, it is just seed. Some Cattleya seed pods have been estimated to contain about 4 million seeds. Orchid seeds are about 0.4 mm long. In the wild fungi growing around the roots of orchid plants provide the necessary nutrients to orchid seed that falls around the parent plant when the pods burst and release the seed. Even in the presence of these fungi very few seedlings survive; hence orchids produce vast amounts of seed.
For us to grow our seed we must artificially provide the nutrients that the fungi would supply in nature. To supply these nutrients it is necessary to germinate orchid seedlings in a laboratory, where germ-free conditions can be provided. Without these conditions fungi in the air would rapidly grow on these nutrients and smother our germinating seedlings.