Preface – Stressing Our Flower
Having written the article ‘Stressful Times’ (below) for publication in the 1997 NCS (UK) Yearbook, I thought it time to bring the subject up again. Let’s quickly start with a fairly hypothetical, esoteric definition of stress in a plant:
‘stress is anything that causes the plant to divert photosynthetic energy (sugar) away from increasing bulk.’
Let’s think about what we’re saying here. To get the biggest, most well formed, colourful flowers (the aim of all sections in the classification list, not just large exhibitions) we need the biggest, balanced plant we can get. Of course if we grow incurveds or singles for example, the cultural strategy will be different, but nonetheless the theory is the same. To get such plants we can’t afford to waste any of sugar produced via photosynthesis. When a plant is stressed through wilting for instance, it is thinking about survival, not increasing bulk. It starts diverting the sugars away from physically getting bigger into making substances capable of helping it protect itself from drought. Likewise if a plant is being underfed at anytime in it’s life, it starts breaking down substances in the lower leaves and recycling them to help counteract the lack of nutrients coming in through the roots. This costs energy and results in a rapid slowdown of growth and ‘bulk’. Ultimately therefore the potential of getting that full sized flower is irrevocably lost.
I contend that anything that ‘costs’ energy is a bad thing and best avoided. There will be enough unavoidable natural drains on the photosynthate (e.g. wind stress, heat stress, pest damage, etc.) which means that any we cause as growers is just not helping the plant achieve it’s very best.
Food for thought.
Ask any grower of large exhibition chrysanthemums for his climatic nightmare and you’ll probably get the answer a warm, wet October. Imagine my reaction then, upon watching the redoubtable Bill Giles give the weekly farming weather forecast of a Sunday lunchtime, when he gleefully utters the words,
‘Winds straight from the Azores. The weather for the week ahead will be unseasonably mild for late October with record high temperatures.’
The inevitable consequence for me is soaring humidity and, of course, the greenhouse temperature must likewise be raised to avoid damping. Twelve months of careful timing are then thrown into chaos as flower after flower disappears rapidly into the wheely-bin. Few other periods of the season are as stressful to the ambitious grower !
Few people, myself included, would claim to comprehend the physiology of plant growth, yet in theory our beloved ‘mums’ need but four things. Light for photosynthesis; water to maintain the transpiration stream, and carbon dioxide together with nutrients in order that a whole host of quite complex organic compounds can be synthesised. As observant growers we soon become quite expert in the response of the plants to excesses or deficiencies of these fundamentals of life. We endeavour to manipulate each to grow a plant which, experience tells us, will produce a good flower. One unlisted factor though I now believe to be a key to success is stress; the best flowers being borne of plants suffering the minimum amount of it throughout their lives.
What follows is a brief journey through a plants’ life from the perspective of controlling the environmental stresses and strains to which our plants are subjected. The article perhaps challenges some of the established ideas, and is intended to provoke the reader to question how the plant may feel about the treatment we are giving it.
Growing any crop essentially equates to controlling the influence of five external variables on the plants: namely air, light, temperature, moisture and nutrient availability. The key to success being how each influences the quality of the four growth phases; i.e. roots, stems, leaves and flowers. At any given moment one of these variables will be limiting the quality of growth we, as growers, are achieving. Our ultimate aim is a plant with roots sufficiently vigorous so as to maintain steady development from a small plant to bloom maturity; with a stem as thick as possible but without hollowness, and leaves as big as possible but without being brittle or necrotic. The resultant flower will therefore be large, colourful and have form commensurate with the cultivar. Any excesses or deficiencies of the five variables encountered during the life of the plant will cause it stress, and result in a plant away from this ideal. Such a plant is then not a good candidate for producing the ideal flower.
Observations would suggest that reducing stress results in faster plant growth of increased quality. Why then root on Christmas Day when late January is capable of giving a better result ? Personally my rooting and stopping dates are now far later than I previously practised. As for cultural detail, a fresh, actively growing, quite small cutting is inserted into a medium containing some nutrient, with a view to filling a Plantpak 24 with root in about 25 days. Potting up occurs after four weeks in order to maintain the developing growth momentum.
In these early days of spring it is light that is limiting our growth quality, and temperature our growth rate. That said, the 3.5 and 5" potting stages are viewed as a key foundation stone to achieving good growth in the bright, warm summer months ahead. Development of the plants must be steady and uninterrupted from removal from the propagator to the cutting of the flower. Stems and leaves must be gently pushed forward to increase the vigour of the plant. The long ‘V’ so often sort by the late Harry Randall must surely be the aim for most cultivars, both in footstalk and lateral. To this end, feed is freely given to all plants in both 3.5 and 5" pots from about four weeks. No stressful flagging is allowed; air being let into the compost to the point of the top leaves of the plant changing colour, but no further. The greenhouse temperature is maintained above 45 Fahrenheit until at least the end of March, as this encourages more root growth. The potting medium is of an open structure, yet moisture retentive, with a balanced nitrogen to potash ratio. Too much potash at this stage is as stressful as too much nitrogen, for either in excess will take the plant out of condition.
A young plant is now obtained with fresh, mid green leaves from tip to toe; with a thick, sappy stem capable of further expansion later in the season, and a fluffy white root system encircling the whole pot. The highly recommended desire to produce a ripe plant by withholding water, enjoying seeing the plant wilt, not feeding early on and growing cold does, in my opinion now, lead to problems later in the plants life. Such treatment induces stress, the plant is less vigorous than the ideal, and it seems able to remember this spartan treatment even when growing conditions are much improved.
Pest control is viewed upon as a necessary evil throughout the summer period. In general, all agrochemicals are phytotoxic to a greater or lesser extent, for each weakens and stresses the plant. The ideal has to be not to spray at all, but an attack of pests cannot be entertained either. In essence it is far better to use an effective contact chemical to eliminate a developing build up, than to indiscriminately expose the plants to systemic chemicals. Trials on commercial chrysanthemum crops are now showing that clean, unsprayed plants produce better flowers than a plant given a typical amount of chemical control. Cleanliness of the local environment is a key factor in reducing pest infestations, and it is here our chemical attacks are best aimed.
Throughout their lives on the standing ground the plants are fed at each and every watering. A little and often strategy is applied, with a careful eye kept on the analysis of the feed. Particularly here in the south-east, the plants require plenty of nitrogen to ensure the steady development we seek is achieved. Phosphate levels in the feed should be low, I believe, as comparatively little of this nutrient is taken up during the summer, and continual feeding of it results in an unacceptable build up. Barry Machin’s article in the 1995 yearbook eloquently summarises the theory and treatment required. The control of nutrient availability is surely greater with a liquid feed, hence this method of feeding is used. The state of the plant, in view of the prevailing weather, will determine the feed given. A poor feeding pattern will undoubtedly lead to substandard growth. The plant becomes hungry and stressed, and particularly if this occurs around bud initiation time, results will be poor.
Counting down of the laterals is also done with stress in mind. Come mid July the plants, with all this feed, are becoming quite large. Transpiration is at its highest as the upper leaves have yet to develop that glaze that comes with bud maturity. My programme for reducing to the number of laterals required has therefore one eye on the weather, and the other on the natural petal count of the cultivar. Hot July weather will naturally reduce petal count, as in 1995, and so that spare lateral must be removed early. A cooler July, as in 1996, will allow the retention of this lateral for longer, but still give an adequate petal count. The plant will then benefit from the increased leaf area and nutrient uptake until later in the season.
If all has gone reasonably according to plan, noticeably larger buds will develop on plants that are still green and healthy to the bottom of the footstalk. These leaves are now retained at housing time, and it is only during the six weeks or so in the greenhouse that I loose colour in the lowest leaves. Feeding is stopped temporarily, from calyx split to petal fall, to avoid pushing growth too hard when but subtle changes are occurring in the plant. It is resumed on all but the softest petalled cultivars though, given that physiologically there is little difference between the growth of petals and leaves.
Andy Wickham 7/3/02
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