Gardening Society - January 2018 report

Pot Mums for Mothers’ Day and other Curiosities       

Dorothy and Andrew Richards

Writing a potted version of our talk about ‘Pot Mums’ will be quite a challenge but here we go!

Dorothy had always been puzzled by the little house plants advertised on market stalls as ‘Pot Mums’. The proper name, ‘Potted Chrysanthemums’ was far too long to go onto the notice boards stating the price of £3.99 so ‘Pot Mums’ was quite understandable - that wasn’t the problem. The real problem was that they shouldn’t be there at all – chrysanthemums flower in autumn and not in March, just right for Mothers’ Day.

Getting the explanation of this took me back a long way – to Charles Darwin, the scientist most famed for the Theory of Evolution. Charles did experiments on plants and their response to light. Everyone knew that plants bend towards the light but do they need a bright light? He discovered that a plant could ‘see’ the very faint light from a distant candle. This made him wonder about which part of the plant detected the light so he experimented and found that it was the tip of the plant that could ‘see’ the light and deduced that the tip must send a message down the stem to make it bend. We don’t realise that this is going on in all of our plants.

Moving on a good few years, in 1904, tobacco farmers in Maryland USA found that some of the seeds they were using had undergone a genetic mutation and were now producing much bigger plants. This was good news as tobacco is made from the leaves and bigger plants meant more leaves. If they could collect the seeds from these bigger plants they could get a much better crop and financial return. There was one snag! This new variety was not like the original one which flowered and ‘went to seed’ at the end of the summer. It just kept growing taller, (was nicknamed the Maryland Mammoth) produced no flowers and then was killed by frost as the winter arrived. After about ten years, the US Dept of  Agriculture decided to work on this. How could they make the plant produce flowers? They decided to try limiting the amount of light by potting up some of the plants and taking them into a dark building each afternoon. This worked!    

But why?

Here is the explanation. The new variety was a seriously ‘Short day’ plant. It flowered when its number of daylight hours was short and it had many hours of darkness. We have discovered, since, that plants can measure hours of darkness and that some plants, like this new variety of tobacco and the many varieties of chrysanthemums, come into flower when they regularly have many more hours of darkness than daylight. The darkness must be continuous – a bit like getting a good night’s sleep.

Now that we know this, we can manipulate the flowering time of plants. So, just before Chrysanthemums, grown in polytunnels for the cut-flower trade, start to flower in Autumn, lights are put on for a short time in the night, right thro’ autumn and winter. This prevents flowering. Then, a couple of weeks before Mothers’ Day, this is stopped so that the plants get a long uninterrupted night. Very soon they start to flower, about six months late.

Another problem is that the potted chrysanthemum plants that we buy are only a few inches or centimetres tall. This is achieved with a chemical that stunts growth. It will be interesting to see how long it takes for this chemical to be used up so that the plant reverts to normal height. I look forward to testing this.

So much has to happen to get the ‘Pot Mums’ for Mothers’ Day that is amazing that my Tesco version was only £4.00 including gift wrapping!

The second part of the talk was about micro-propagating plants. Garden Centres and plant nurseries do not reveal which plants have been produced by micro-propagation and which by normal vegetative means. A trip to Fairweather’s wholesale nursery in Beaulieu, last summer, proved to be fascinating. Agapanthus are produced there, to supply the trade in this country and Europe, all by ‘micro-prop’ as it is known.

A tiny piece of plant, probably the growing point, is placed in a sterile dish containing chemicals that stimulate the growth of shoots. In a few weeks there is a handful of them, looking like a ball of blades of grass. These are then transferred to another sterile environment where chemicals promote the growth of roots so that in a few more weeks there are tiny plants ready to pot into cells of usual growing medium. From this stage to a garden sized agapanthus, ready to flower, takes about four years, but, at least hundreds can be grown this way.

There are several advantages of this technique. Plants that are in danger of dying out, because of disease or loss of habitat, can be restocked. Newly bred varieties or rare plants can have their numbers bulked up by this method and sterile plants such as double primroses or some geraniums can be propagated. Sterile plants do not produce any seeds so have to be propagated like this or by the much slower method of root division or cuttings. This method of micro-prop does not work for all plants but it is a major part of the horticultural trade.

The Fairweather’s nursery opened for the National Garden Scheme during the last weekend of July, to coincide with the Agapanthus flowering season. They have the National Collection of agapanthus and they have many plants for sale to the public on their open day. Entrance was £3.00, which goes to the NGS charities, and the guided tour of the nursery was included in the price. At the end of the explanation of micro-prop, a friendly lady remarked ‘Well, how weird is that, I thought plants grew from seed.’ She summed it up for most of us in the crowd that day.

Our meeting on 29th March is an illustrated talk by two of our members. Judy Villiers and Liz Waterman, both keen and successful gardeners, are going to tell us about ‘Vegetables, Flowers and Sculptures’ in their gardens. They have been taking photographs, throughout the gardening year, to show us how they go about the different jobs, the varieties they use and the success (or sometimes failure) they achieve. New members and visitors are most welcome, 7.15 for 7.30pm in the Reading Room, SP1 3LL, where there is a free carpark.

Dorothy Richards