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Firstly, let it be clear that colchicine is a dangerous substance which needs careful use and disposal.

N.B. In the UK, Sigma/Aldrich (and other suppliers too) will not supply colchicine to individuals who cannot provide evidence of qualifications and/or experience fitting them to handle dangerous substances.

None the less, for those so qualified, it is possible to use colchicine safely and successfully to promote polyploidy in orchid seedlings. Dr Donald Wimber has been a recognised authority on this business for many years. He was a co-author of a paper in the Lindleyana in 1988 which gave details of a controlled trial of polyploidy induction in paphiopedilum seedlings. Colchicine was used in three different concentrations for 3 to 25 days on protoplasts at three different stages of growth.

From this the authors found that :-

1, Protocorms should not be too advanced in growth when treated - up to the stage when they are green and just starting to produce the first leaves.

2, About 7 days in contact with the colchicine should produce good conversion rates, longer treatment caused many seedlings to die.

3, Filter-sterilised colchicine was effective at a concentration of 0.005%.

4, Heat-sterilised colchicine was effective at a concentrations of 0.05% and at 0.025%.

The paper gives a very thorough treatment with the results in great detail, but the above is a very rough abstract of the 'nitty-gritty' as it affects small scale use by the 'serious hobbyist'!

Colchicine is reported to be destroyed by heat, so sterilisation by cold filtering permits use of less colchicine per flask. However, suitable filtering equipment is not cheap - ( one has to pay for more than is likely to be used within a reasonable space of time) - so for small-time use at home it seems best to use a 0.025% or 0.05% strength colchicine solution, adding this to flasks before they are sterilised.

In fact, I have been informed by those who have considerable experience of using colchicine that it is quite heat-stable when used with agar and water only. (For the paper cited above, the colchicine was added to normal orchid medium and it may be that the salts in that medium were more responsible for instability of the colchicine than the exposure to heat. - Personal communication from Robert M. Hamilton.)

Sigma sell colchicine in lots of 100 milligrams (or larger). It arrives in a small plastic bottle inside a bag inside a large plastic bottle - clearly marked as containing toxic material. Inside the small bottle is what looks like, and is, a very small amount of fine white powder.

To avoid having to handle this powder it is best to make up a solution containing all 100 milligrams at one time. To produce a 0.025% solution use 400 ml. of water, or 200ml for 0.05%. The article I mentioned above describes using a normal nutrient medium, but for one week it seems adequate to use a plain agar solution to which the colchicine has been added. This should allow successful use of 0.025% concentrations. Dissolve 2.8 gm. of Sigma agar in 300 ml. of water, add the colchicine ( uncap the colchicine and pour a little of the remaining 100ml. of water into the colchicine bottle. Replace the cap and shake and swirl to ensure all the powder dissolves in the water. Pour into the agar solution and mix in. Add more water to the bottle and empty into the agar. The bottle and cap can then be rinsed again and disposed of safely (only minuscule amounts of colchicine can remain by then).

Finally, add the remaining water so that all of the 400 ml. is used in the mix.

This mix should be a fairly solid one. This ensures that it is not too difficult to remove the seedlings from the colchicine mix when the time comes.

It would be advisable to wear gloves and a mask when handling either the colchicine or medium containing it so as to avoid hazard if an untimely cough, sneeze or spill should occur.

As the medium is only to be used for a week only a small amount is needed for each bottle - I usually make this mix produce ten or eleven bottles. The bottles can be capped and heat sterilised by your usual method. I use baby food bottles with foil for the seals - the bottles do not need to be vented as the seedlings are only in them for a week and there is no banana or other ethylene producing ingredient in there!

After re-plating the protocorms, the bottles can be incubated for a week in your normal incubation set-up. After about a week (5 to 10 days) the protocorms are re-planted again into your favourite medium and treated from then on as usual. Be sure to label the bottles after re-plating as having been colchicine treated so as to avoid confusion later between treated and untreated seedlings.

Agar/colchicine bottles not used immediately can be stored for several weeks after capping and sterilising.

After the seedlings have been re-planted out of the colchicine mix, the used medium must be disposed of. It still contains colchicine. It should be disposed of safely - check your local regulations and comply with them - it isn't nice to damage the local fishes etc. In any case, I like to melt the medium in hot water and dilute it considerably before disposal.

So far I have treated a number of species and hybrids using this method. Most have had a reasonable survival rate - some plants appear more sensitive than others. As to whether I have many tetraploid seedlings; time will tell. None are flowering yet (or for some time to come) and none are yet large enough to have root tips chopped off for chromosome counting - the only way to be sure what the ploidy is. Compared with untreated members of the same batch of seedlings growth of these colchicine treated seedlings is slow at first but picks up later. The general experience is that colchicine treatment will convert around 25 per cent of the seedlings to the tetraploid state.

Bob Hamilton has been the main source for most of the information I have on this subject, including the above. Many thanks to him for this. See his many postings on this and other matters. ( Any errors in the above are my own - the information was all OK before I started messing with it!!! )