A timely purchase
Published:
HERE we are, just into April and still battling the elements to get the spring work done. I know you have made a start because the questions have started to roll in. For instance:
From June Hodge comes a familiar tale: “You keep telling us not to put out tender plants until the end of May, but when I wait to buy them nearer the time, I can never find the colours I want. What am I to do?”
Answer: I didn’t say “don’t buy them now” and I do agree with your point but simply warn that if you bring plants home this early, you must have somewhere to keep them, under cover, in full light and frost free.
The obvious place is a greenhouse or cold frame, but if severe frost is forecast, you will need to cover them with a few layers of fleece if you are unable to heat the space.
Remember the Sid Robertson tale when he was explaining this to a client who insisted that the windowsill would be fine because it gets plenty light?
“From one side only, dearie. At this time of year, young plants need good light from all sides and the top forby.”
I am particularly anxious that the light is good, otherwise plants become leggy and easily broken when they have to be moved. The problem is made even worse if the temperature is too high.
There isn’t usually too much compost supporting these young plants, and here you have a choice. Either you prick them out (if they are seedlings) or pot them up (if they are in plugs or small cells (I’ve seen some plugs that are not much bigger than a thimble). As well as giving more compost to increase the size of the root system, this will also give them more elbowroom to grow into a rounded and balanced shape.
Alternatively, where space is at a premium you can give them a weak liquid feed to keep the plants from becoming hard and woody. You must realise, however, that the first option is by far the best.
The other implication of taking in bedding and basket plants this early is that by the time you do come to plant them out, if you have looked after them well, you won’t need so many because they will take up more space.
In this regard, as I have reminded you before, it pays to nip out the growing tips of shoots that start to sprout vigorously; as a result, your plants will have more flowering shoots, creating a really good display.
Question: This is another belter from Clive Anderson (no, not that one. This one lives in Aberdeen). He has just put up a new greenhouse and is anxious to be getting on with things. Already he has realised that it gets quite hot in there, between the snow showers, when the sun comes out. Should he leave the ventilators open all the time?
Answer: Yes, if you are growing some of the difficult Arctic alpine plants that simply need shelter from the wet. Otherwise, ventilators should be opened only when essential to keep the temperature from becoming excessively high; in high summer, that might be, say, over 25C.
It is really essential to fit automatic ventilators that respond to rising and falling temperatures such as the situation we have experienced in the last week or so. These units don’t need any power and most of them can be calibrated roughly to start opening when the desired temperature has been reached. Some manufacturers have a model that can be fitted to louvred ventilators. Prices vary from about £20 upwards.
The supplementary question to that is: “Why don’t you just leave the ventilators open all the time, or even prop the door open?”
And the supplementary answer is: “Not on your Nellie.”
A glasshouse is intended to provide a growing environment for plants, either when the outside conditions are not conducive to active growth, as now, or in order that you can grow plants from other climates that will not grow in the open in this country.
Apart from protecting against excessive rainfall and wind, a glasshouse allows plants to grow in a higher temperature – what’s the point if you are going to leave the vents and door open all the time?
The rules are fairly simple – in the closed environment of a glasshouse, you can provide a growing climate. If the temperature protection is not enough on its own, you have to heat it.
If it starts to get too hot, you allow fresh air in using just enough ventilation to maintain good growth. As the seasons change and ambient temperatures rise, you need to have more ventilation to prevent overheating. If the ventilation system is automated, that balance can be maintained.
At some stage, perhaps because there is not enough ventilator area, the temperature may continue to rise dangerously high. Then, and only then, is it acceptable to leave doors open.
Another story from the past. During my time at Auchincruive, I had a spell in charge of the temperate glasshouse range, looking after displays of pelargoniums, fuchsias and a whole range of popular flowering and foliage plants.
One May morning, it started to get quite warm and I opened the side ventilators, allowing air to come in near floor level and out at the ridge. I thought I was being quite smart, as you do when you are in your early-20s and feel you already know it all.
In comes the boss-man, John Warwick, for one of his unannounced tours of inspection.
“Get these bottom vents closed, laddie. At this time of year, that is not ventilation, it’s a draught.”
The next question comes from John McCallum in the Mearns:
“My ground is just about ready to start sowing and planting and I have an onion problem that remains unsolved. Last year, a rot affected the crop. At the base, there was a cotton wool-like growth with black specks in it, and this seemed to be rotting the bulbs. Any cure, because I’m scared that it might return this year?”
Answer: You have very adequately described White Rot of Onions. The worst attacks I have ever seen have been in crops of spring onions, but it does affect the onion family. The fungus is Sclerotium. Unfortunately, this disease is a bit like the Eelworm that affects potato crops – it can remain in the soil for many years.
There is no control that I know of and the only way I can suggest that you can continue to grow the onion family is to observe strict rotations, sowing and planting into soil that has remained “clean” while trying to prevent any cross-contamination – and I know fine that is not easy in a small garden.
