This is a real cracker
Published:
I FIELDED a question last week that I thought had to be answered rather tactfully because, otherwise, someone was likely to be upset. Well that was my reading of the situation from the outset, but in this modern society, there is nothing quite the same as it used to be and it tends to catch out blokes of my vintage. I refer to stereotypes.
Let me explain in very simple language – the question was asked, “Can you sterilise soil in a microwave?”. My problem was that the query came from a “she” – see what I mean?
The answer is a qualified “yes”, but I would suggest that it is ill-advised because there is no way of knowing for how long, and how much can be done at any one time, taking into account the capacity of the microwave.
The question arose because the perpetrator had tipped out a pot of lily seedlings to find the soil at the bottom heaving with vine-weevil larvae.
Having separated them out and completed the “dance of the damned”, she then paused to think, “there may be more nasties in this compost that I can’t see and I hate throwing out good compost. I could sterilise the compost and then be able to use it again safe in the knowledge that it will be clean”.
Quite so, but what damage might be done? Let me return to the whole topic of “sterilising” soil. Why would you even think of such a thing?
My first experience of this technique, used in two separate operations, was during my pre-college year working on a mixed market garden nursery on the outskirts of my home town, Kilmarnock. At that time, the compost used for seed sowing and growing plants in pots was loam-based.
The loam was cut from a field that had been sown down to grass for grazing. It was cut like lawn turf is now and stacked in an open shed upside down until it rotted down. It would then be shredded and loaded into a box cart fitted with a grid of pipes on the bed. These pipes had upward-facing holes in them. The cart was then moved to a point next to the steam boiler, the pipe grid connected to a steam outlet and the tap turned on. With a heavy tarpaulin fastened over the cart, the soil was “steamed”. The process might take anything from 30 to 40 minutes for each batch.
The purpose of the exercise is to kill pest and disease organisms that may be lodged in the soil, and the bonus is that weed seeds and roots are killed off, too.
The other steaming operation relates to glasshouse-grown crops. At one time, the entire body of soil in these great glasshouses – used to grow tomatoes, cucumbers, lettuce and peppers – was sterilised to a depth of 15-18inc. Once again, the sole purpose for carrying out this labour-intensive and expensive operation was pest and disease control. It was a gruelling task, I can tell you.
Latterly, steam sterilising gave way to chemical treatment. And, of course, in pot culture, soil-based composts gave way to the soilless composts we are so familiar with today. All ingredients would be deemed to be free from harmful organisms.
To go back to my starting point, you can still purchase little electrically heated boilers for steam sterilising loam; indeed, we have one at Beechgrove. These will allow you to monitor temperatures to ensure that you don’t overdo the operation, because that would lead to the destruction of some of the physical properties of the soil/compost as well as altering the chemistry. In other words, it can be overcooked.
For the record, the effect of higher temperatures on living organisms in the soil is as follows:
At 54C, earthworms, eelworms and some bacteria are killed. Most fungus diseases are killed after about 10 minutes of 43-63C, but some wilt diseases will only succumb when it reaches 82C. Most plant viruses will be knocked off by the time the temperature reaches 88C. Now who said I wasn’t a mine of useless information, eh?
If you can check the temperatures in the microwave, madam, and you have the permission of the chief officer of the kitchen, you may well continue to use this method of pasteurising your soil. There are others out there who use a kitchen “steamer” pot!
Hardening off plants
These few days of slightly better weather may tempt some of you to start putting young plants outside. That is absolutely fine, but do be prepared to cover them up if there are heavy downpours of rain or if the temperatures get down to around zero.
Having been raised indoors, the foliage of most plants is quite soft and, in some cases, brittle because they are protected from strong cold winds and heavy rain. A strong dose of either will set them back significantly. Copious amounts of freezing cold rain will chill the compost and, in turn, the plants.
The drill used by professional gardeners is to place the plants in cold frames with the lids on, but propped up wide, or even removed, in bright weather. They are always kept to hand, however, to put back over the plants in the early evening, shutting them tight if frost is forecast to trap a bit of heat inside, but leaving the covers propped open a little during mild nights.
The technique is well named – harden off the foliage, but do it gradually.
The other side to this is being over-cautious and, as a result, you finish with soft, blousy plants that get far too big and unmanageable before you can plant them out. Success comes from keeping a watch on the various different types; if they are seen to be growing too fast, slow them down – that is usually done by reducing the growing temperature while still giving them maximum light.
Trellis
I enjoyed Morag Lindsay’s piece on Trellis which appeared in the Press and Journal last Wednesday. Apart from being personally involved with the organisation, for many long years now I have been championing the role of gardening in the whole area of therapy. Most people you speak to have an example from within their own family of how gardening helped restore someone’s physical health or piece of mind, or simply gave them something to live for, something they could participate in that gave some meaning to life.
The good news is that organisations such as Trellis are now recognised by the authorities for the extremely valuable work they do. They all deserve our support.
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