Dry Seed Flasking Guide
  • By Wolfgang H Bandisch
  • Posted April 10, 2016

A Beginner's Guide to growing Orchids from Seed: Dry Seed Flasking

Many articles one can find on this subject stress that flasking can be done under rather 'primitive' circumstances, like in a plastic bag, over a saucepan with boiling water and the like. This article describes the procedure using a home-made laminar flow cabinet.

Dry Seed Flasking Guide

There are many ways 'to skin a cat' and many different procedures to flask orchid seeds. Seeds can be flasked dry or green. Dry seeds are obtained from fully ripened capsules. It is important to understand that such seed gets immediately contaminated once exposed to air and will need to be sterilized. Green seeds are obtained from capsules that have ripened for at least two thirds of their normal gestation time. It is a matter of judgment that can only be obtained with some experience over a period of time. Since the seed inside the closed capsule is considered sterile no sterilization of the seeds is necessary. Both methods will be explained in detail here.

In this article I describe the procedures for flasking of DRY seeds. This is not necessarily the only way to do it but this is how it has worked for me. One person alone can do it but it is much more convenient to have someone to assist with a few little chores.

Required Equipment

You'll need the following equipment and consumables:

  • Laminar Flow Cabinet - I think that this is absolutely necessary to ensure success. Some great models from Air Science, based on budget are:

  • Pressure Cooker - Unfortunately another rather expensive item but any household pressure cooker with do fine. If you don't own one, here are a few options - just pick one based on budget:

  • Graduated Measuring Container - At least 2 are needed, one to measure 1000 ml (i.e. 1 liter), and one to measure 200 ml. Again, if you don't own any of these, you can get them here:

  • Flasking Medium - Seed flasking medium and replate medium can be purchased pre-mixed from a number of suppliers in most countries. There are many different formulations available but for the beginner a complete medium with sucrose and agar is most advisable. The media are generally in powder form.

  • Distilled Water - This is needed to prepare the flasking medium and can be purchased in supermarkets in 2 liter plastic bottles. If you'd like to buy some online and have them delivered, here an option:

  • Quantity of Flasks - Any kind of glass or re-sealable plastic/polycarbon container can be used. Preferably these should be of uniform size for reasons explained below. I use polycarbonate Erlenmeyer flasks with a screw cap and breather hole - I find these a lot more convenient than the Erlenmeyer flasks that need to be closed with a cotton bung and sealed with aluminum foil.

  • Timer - Sterilizing the flasks in the pressure cooker and sterilizing the seeds in a bleach solution has to be timed. A cheap egg timer is fine.

  • Scale - An electronic letter scale is perhaps a good solution. Unless you want to prepare flasking medium from scratch (not advisable for the beginner) such a scale will be all you need. You should be able to weigh between 8 and 50 grams with reasonable accuracy.

  • Bits and Pieces - A pair of dish washing gloves to protect your hands during the operation from the bleach solution. A spray bottle to dispense the bleach mixture inside the cabinet and to spray the flasks entering the cabinet is a must. A thick, strong cotton cloth to lay on the working surface. Get some plastic test tubes with screw cap from your local pharmacy to be used for seed sterilizing and while you are there get a few plastic syringes and large gauge needles to remove the seed as explained below. Non-absorbent cotton wool to plug the breather holes.

    A waterproof marking pen and some fabric self-adhesive tape to number your flasks and a notebook in which you can record what you are doing are needed.

    For convenience, I've listed most of these items below for purchase online - but you can use what you have at home or from your local shops:

Preparing your Work

    1. Prepare your flasks. Wash them thoroughly in hot water and let them drip dry. When you use jam jars, tomato paste jars, honey jars etc. try and select those of roughly the same size, make sure that the lid can be tightened securely. When flasks with 'breather holes' are used, these need to be plugged with non-absorbent cotton wool.

    2. Take the 1000 ml graduated container and fill it to 900 ml with distilled water. Add the motherflask medium. (follow manufacturer's instructions as to the quantity of medium required to make 1 liter, weigh as accurately as possible). Mix the powder with the water, stirring continuously for not less than 5 minutes to dissolve the agar and sucrose contained in the medium. Fill the container used to measure the powder with the remaining distilled water, swirl container to remove all traces of the powder and add to the rest of the mixture to end up with 1 liter of mother flask medium.

    3. Bring the mixture to the boil and simmer for a few minutes, continuously stirring to dissolve all ingredients evenly.

    4. Fill flasks with the medium, about 2-cm high and try to fill flasks with even quantities of medium. This is quite easily achieved if uniform size flasks are used. Fill one jar with distilled water.

    5. Fill the bottom of your pressure cooker with about 5 cm of water and place flasks with the medium and the flask with the distilled water inside. Sterilize flasks for 20 minutes at 115-120o C. Try to keep the temperature during sterilization as accurate as possible. Do not over-cook or extend the time as this might alter the formulation of the medium. After sterilization let the flasks cool and the medium solidify. This will take at least 2 hours.

  1. Open your notebook and enter the date and write down what you have done so far, like which kind of medium you have used, what kind of flasks etc. On a separate page write down the name of the orchid's seed you will be flasking, species or hybrid, date when capsule was set and date when capsule was harvested and whether this was dry or green seed. It is also helpful to note down from whom this seed was obtained or the region where this particular plant was found. Write down the number of flasks you will seed with this particular species or hybrid. Leave some space for comments such as the date of germination, eventual contamination and for later a column where you can enter the date when you will replate your seedlings and the number of flasks to be replated.

    Carefully select which seeds you want to flask and fill a little of each variety into one of the tablet tubes you have on hand. The seed should be free of debris, dried parts of the capsule etc. Write the number or other kind of identification on the tablet tube. Store remaining seeds in a small envelope, tightly sealed in the refrigerator.

Dry Seed Flasking Process

  1. Start up your laminar flow cabinet. Turn on the clean air filter. The filter should run for not less than half an hour before you start working. If the cabinet is equipped with a UV light, this should also be switched on at the same time. Beware of the UV light. Never look into the light. Permanent damage to your eyes can be the result.

  2. Prepare the sterilizing solutions from bleach. Two strengths of bleach solution are needed. One to sterilize your work area and items being moved in and out of the cabinet and one to sterilize the seeds.

    Use the 1000 ml graduated container and pour in 200 ml bleach (e.g. Snowite, Chlorox) and add 500 ml distilled water. Normal tap water is also okay. If normal tap water is used let it run for a minute or so in case there is any debris in the pipe and use it then. Fill the spray bottle with this mixture and thoroughly spray the inside of the laminar flow cabinet - but not the clean air filter - until it is soaking wet. Place the cotton dish washing cloth in the center of the cabinet and spray it with the bleach solution.

    Decant a small amount of this solution in a deep dish, large enough to stand one of the flasks inside. Decant another quantity in an empty flask or glass and place syringes inside. Place the dish and the glass inside the cabinet.

    For the seed sterilizing solution decant 100 ml of the solution in the 200 ml container and fill it up to 200 ml. Get a toothpick and obtain a minute amount of dish washing detergent. Add this to the mixture. It will help to break the surface tension of the water and allow the sterilizing solution to get into the entire surface of the seeds to be sterilized. Too much detergent will result in excessive foaming.

  3. When the medium has turned solid you are ready to start work. Cut small pieces of self-adhesive tape and stick them on the flasks. Write the identification number of the seed on the tape. Place bottle with distilled sterilized water in deep dish inside cabinet.

    Switch off UV light. Put on the dish washing gloves and sit in front of the cabinet. Spray the inside of the cabinet, the cloth and both gloved hands thoroughly with the bleach solution

    Get your assistant to pass the flasks to you by first placing them into the deep dish. You take them out form the dish and spray them thoroughly with the bleach solution. You are now working in a sterile environment. Keep it sterile, use the bleach solution liberally and avoid sudden movements. Never cross your arms, learn to work from left to right or vice versa, whatever is convenient.

    Your assistant will now fill one of the tablet tubes containing seed with a small amount of sterilizing solution from the 200 ml container. Turn the timer to 8 minutes and start shaking the tube - outside the cabinet. When the time is nearly up have the tube placed in the deep dish, take it out, spray it thoroughly with the bleach solution and observe whether the seed is sinking, floating or stays suspended in the liquid.

    Prepare the syringe by attaching the needle. Keep everything sterile. Extract the sterilizing solution with the seed from the tube and eject the sterilizing solution leaving the seeds behind. This is sometimes quite tricky and will take some practice not to decant the seed with the liquid. With the seed inside the syringe suck up a little of the distilled, sterilized water and wash the seeds. Depending on how many flasks are to be seeded leave 1 ml of distilled water per flask inside the syringe.

    The next step needs to be done quickly. Unscrew the lid of the flask to be seeded but leave the lid on the flask. Hold syringe in right hand, with your left hand lift lid of flask, shale syringe and quickly eject about 1 ml of liquid with seed into the flask and close lid immediately. Repeat with the remaining flasks. Now with both hands tightly close lid of flask and spray flask with bleach solution, especially under the rim of the lid.

  4. Store flasks in a dry place with normal light. Important is that the storage place is not subject to severe changes in temperature. Around 22-25 degrees C. is most adequate for orchids. Do not place flasks in direct sun. Observe flasks daily for any sign of contamination. Write down the date of germination in the notebook and also if and when contamination occurred and its colour.