Pinching and Pruning bedding plants
If you want a really good flower display there is one job you shouldn't avoid and that is occasionally pinching out and then pruning your bedding throughout the season.
For most plants, as soon as they come into existence, the race is on to ensure a good position, as close to sunlight as possible so that they can get maximum energy from the sun. A plant must assume that there will be other plants around it, all capable of shading out those precious sun rays and so it must get its head as high as possible.
The job of reaching the finishing line is given to the highly-competitive, alpha-male, terminal bud. First to appear and usually at the tip of the main stem, it is also known as the apical meristem. The apical meristem has one thing on its mind and that's to reach a postion where it has sufficient sunlight to produce a flower, set seed and thus ensure the survival of its species.
Not only does the apical meristem have to compete with the plants around it, it has to compete with the lateral (or side) shoots further down the main stem as well. To do this, it produces a hormone which inhibits the growth of the lateral shoots. Only when the terminal bud is far enough away from the other nodes which produce the lateral shoots does it lose its hormonal influence over the side shoots. When this happens, the hormone is deactivated and the side shoots can develop more strongly.
So, left to ts own devices, a flowering plant will produce a strong main stem with the flowers concentrated at the tip and some more flowers produced further down when the time is right. For our bedding plants, and particularly for hanging baskets, we prefer a nice, bushy growth with plenty of flowers evenly spaced on the plant and this means we have to prevent the apical meristem from exerting its controlling influence over the rest of the plant.
By removing the terminal bud, we force the plant to engage the next in line for leadership to run the race instead. So the baton is passed to the next buds (axillary buds) down the line and off they go to finish the race. Usually there will be two qualifying axillary buds, one on each side of the node and so you get two 'terminal buds'. Remove these buds after a while and you get four and so on. In the end, you produce a plant which is wide and bushy rather than tall and leggy.
Every time we remove a terminal bud, we prevent the plant from flowering for a number of days or weeks, depending on the plant. So, ideally, pinching out must be carried out in the early stages of plant growth so that we can get the job done and then leave the plant to produce its flowers on the new stems we have encouraged. A good plant nursery will do the job of pinching out at least the original terminal bud before the plants go on sale but this job is highly labour-intensive and in these days of cheap, intensive production, you might find that the plants you buy haven't been pinched.
Below is a trailing petunia demonstrating quite well the difference between a plant that has been pinched just once and one that has been pinched back several times. In the plant on the left, all the flowers are concentrated at the end of the stems. The plant on the right has been pinched back in the early stages to produce even growth and flowers throughout.
The first pinching out takes place on the main, central stem. Go back to the next set of side shoots and with your thumb and forefinger, simply sever the stem just above the side shoots. If the plant has become too tall, you can go back to the second set of shoots. When the side shoots have produced stems which have side shoots of their own, repeat the process on each of the stems and so on until you have the shape you want.
If you've bought your bedding plants in flower as many of us do, you might have to bite the bullet and remove the flowering stem back to the next two lateral shoots in order to get a nicer plant with more flowers later on. The picture below shows the leggy trailing petunia pictured above after it has been pinched back. Okay so we've lost the flowers but, with good, even light, this plant will start to produce side shoots and will be looking a lot better in a few weeks time.
Take care when you are pinching out that the plants you are pinching aren't showing any signs of disease. If your plant has picked up a fungal infection or is being attacked by aphids, you can still save it by pinching diseased plant material and treating for aphids but, in this case, you run the risk of passing the disease onto healthy plants through the wounds you create so you need to wash your hands between pinching.
Once you have the desired shape, stop pinching out, give the plant a good feed and sit back and let it do its thing. You'll be rewarded by a profusion of flowers that will be the envy of your neighbours. Remember though, you have forced the plant to produce more flowers than it might have done if left to its own devices so a liquid feed every now and then with a fertiliser that is high in phosporous will help to compensate for this.
If plants had brains they would very definitely have sex on the brain. Like all living things they have a strong desire to ensure the survival of their species and bedding plants in particular are in a great hurry to do this. It's almost as if they know they'll be killed off by the first frosts and so their window of opportunity is very small. That's why we love them so much. They produce loads of brightly coloured flowers, making every effort to attract pollinating insects so that the plants, in turn, can produce seed.
Understandably it takes a great deal of energy to produce flowers and even more to produce seed so, once a plant has successfully done this, it will want to take a rest. For us, this means reduced flower production or loss of flower production altogether. So, throughout the season, we have a little pruning to do in order to prolong the flowering period.
Most of this pruning takes the form of dead-heading. Dead-heading is simply the process of removing spent blooms before they have a chance to set seed. This not only prolongs the flowering period but also keeps your baskets and containers looking lovely and fresh throughout the season.
While you're checking your plants for spent blooms, prune out any diseased or damaged leaves as well.
So, if you want to have a really nice display of bedding plants, what you really have to do is to delay the plant from doing what is has evolved to do for as long a period as possible. If you think about it, it's just as well plants don't have brains because, if they did, we gardeners would definitely be guilty of plant cruelty. But, just in case they do have feelings, having made the plants do all that extra work for you, you should at least make it as easy as possible for them by pampering them as much as you can. Water your bedding plants every day it doesn't rain to reduce the stress on them and, perhaps when you're doing all that pinching and pruning, a little apology wouldn't go amiss!
Julie is a lecturer in horticulture, editor of Gardenzine and author of the book The Plant Listener