Growing Pleiones from Seed

2. Sowing and Replating

Introduction

Under natural conditions, most orchid seeds are only able to germinate if they form a symbiotic relationship with a fungus, which provides various nutrients the seed needs. This means that orchids cannot be simply sown in a pot in the normal way. Techniques have been developed which can supply the nutrients artificially. This has to be done in flasks under sterile conditions and so has largely been regarded as a laboratory process beyond the means of amateurs. However, “home flasking” or “hobby flasking”as the Americans call it is possible with a little ingenuity and simple equipment.

Sterility  

All sowing and replating (which means moving seedlings from one flask to another) is done under sterile conditions inside a homemade laminar flow cabinet or even a simple “glove box”. I made my own simple laminar flow cabinet. First I bought a cheap, clear plastic storage box from the DIY store. Then from Argos I bought an air purifier – these are machines which are sold for people with asthma or allergies. They filter the air in the room through a very high grade filter (called a HEPA filter) and blow out cleaned air with all pollen and other particulates removed – including most fungal spores and the like. I connected the outlet from the purifier to a hole cut in the back of the clear storage box, using a polythene bag cut into a tube. This simple device creates a sterile environment inside the box in which you can work. All the inner surfaces must be thoroughly wiped down with disinfectant beforehand. A 10% bleach solution is the most effective, but is not very pleasant to work with. I use Dettol (anti-bacterial formula) as an alternative. Any instruments used can also be sterilized with this or (even better) with Virkon, which can be bought from agricultural or equestrian suppliers. Always wear gloves for the whole operation and a plastic coat is a good idea too. Sterility must be thought about at all times and good technique will help in this respect – this comes with practice and experience.  

Making up the Media

The “media” are the nutrient solutions that the seed will be sown and grown on. It can be difficult to find suppliers of media but some orchid nurseries sell it. I like to make up the media several weeks before I actually intend to use it. Then, if any jars are not perfectly sterile these ones will show up contamination by the time you want to use the jars and so the contaminated ones can be rejected. Making up media involves adding the powdered media to water, adding any other additives required and bringing to the boil. The brew is then tested and adjusted for pH and poured into jars. Only about 0.5 to 1 cm depth is needed for sowing and about 2 to 3 cm depth for replating. The jars are then sterilized by placing in a pressure cooker at 15psi (this is the max setting on most pressure cookers) and cooking for 20 to 25 minutes.  

Preparing for Sowing

For Pleiones, I usually sow in December and use honey jars as “flasks”. I have tried various media, including both commercial media and homemade stuff. I find I get the most reliable results by sowing on HALF-STRENGTH Sigma P6668 orchid maintenance medium.  When making up this medium I add 7g per litre of Agar. The Agar turns the solution into a gel, rather like when setting a jelly. I adjust the pH to 5.7 (using a 2.5% solution of potassium hydroxide) before pouring it into the honey jars. I use pH test papers to measure the pH with.  

The day before sowing, I first prepare a solution of one teaspoon of sugar (sucrose) in 250ml of water. That evening, I put a little seed into a small bottle, add some of the sucrose solution and give a good shake. The seed is left to soak in this overnight.  

Sowing

Next morning, the sugar solution is removed with a pipette and replaced with a sterilizing solution. I use Miltons Fluid, sold for disinfecting babies’ bottles etc. Miltons is 2% Sodium hypochlorite. I dilute this at a rate of 10ml of Miltons made up to 50 mls with water. Once added to the bottle of seed, the bottle is dipped into disinfectant and wiped all over with the disinfectant, then placed into the sterile cabinet. I leave the seed to soak for 20 mins in this solution - or 25 for seed I think may be fungosed. After this, the Miltons is removed with a pipette and sterilised water added in its place to rinse the seed. This is removed and a little more sterile water added before pouring the seed into the flask (using just enough water to be able to swirl around to distribute the seed over the medium). Any excess can be carefully removed with a sterile pipette.  

The flasks are then put under fluorescent lights, which are on for 14 hours and off for 10 each day. Temperature is kept between 18 and 25 centigrade. Germination is usually fairly rapid - most are obvious after between 1 to 3 weeks, though some can take much longer.  

Replating

I replate (which means moving the seedlings to a new jar) approximately 2 months after sowing (so mid Jan to mid Feb roughly depending on when I sowed and how quickly they germinated. They should have small shoots about 3 to 5mm high at this stage). For this first replate I use honey jars again and the same media but a bit stronger - 60% strength and I add 80g per litre of pureed banana and 25 mls per litre of pineapple juice, again adjusting the pH to 5.7 (Before adjustment this media is quite acidic and it usually takes about 6mls of the potassium hydroxide to get to pH5.7). The young plants remain on this medium until they go dormant later in the year. I then put the flasks in a fridge (not freezer!!) to keep them dormant - they start growing again fairly soon after if you don't do this.  

I keep them in the fridge until the start of the following year and I then do a second replate in Jan or Feb. For this second replate I use taller jars (jam jars or cook-in sauce jars) to accommodate the leaves, which will grow much taller in their second year. For this second replate I use a different media - Sigma P1056 at full strength and add 50 ml per litre of pineapple juice, again adjusting pH to 5.7. They go back under the lights for the rest of the growing season until they go dormant again. I then put them back in the fridge and then remove them from the flasks in Spring, potting them up as normal plants.