I also make special reference to damping off disease.
|Blogger Sue Garrett recently challenged fellow bloggers to publish pictures of less flattering parts of their garden. If you believe this picture was specially staged you are wrong!
I try in my blog to provide correct factual information. When I fail to do so please let me know. Inevitably in some cases there is a degree of speculation and opinion. You might decide that is the situation today. My scientist friend Peter Williams agrees with the thrust of my submission and agrees dirty pots are essentially the same with regard to plant health as putting new plants harmlessly into outdoor soil. He is adamant however that he will continue cleaning his pots although I don’t think he actually goes so far as washing them.
I am indebted to blogger Rick Nelson for alerting me to this myth. He empathised with me when I previously described washing clay pots outside on a cold winter morning when I worked at Hartlepool Parks and Recreation Department. In those days pots were scrubbed to remove algae and lime. New pots were also soaked and washed to remove salts left from manufacture. Attitudes change, and I remember displaying Dicentra cucullaria in a large clay pot at the Harrogate Spring Flower Show. The dirty earthenware pot was covered with white lime and algal green. It was a star.
I had thought not cleaning my pots and seed trays was part of my slovenly nature. I am grateful to Rick for informing me that I am not unique.
|Ammi was all over the place at a rather hyped flower show last year. I have succumbed to fashion.
Plant health is an essential part of plant management. There will be rare occasions when a dirty plant pot harbours pests such as root aphid or root mealy bug. Heaven forbid, vine weevil larvae may lurk in some peaty compost. You might have even grown cabbages with clubroot . Perhaps your plants were dripping with red spider mite and some have gone into hibernation round the rim of your pot but I doubt it. In none of these events would I clean the pot. I would go further and throw them away.
You may be worried about the fungal fungus disease of seedlings called damping off when the contents of an infected seed-tray keels over and dies. This disease is associated with dirty conditions and unsterilised soil. I have unconventional views about this very important and ubiquitous disease.
We used to teach our students that damping-off was an infectious disease and not merely a disorder caused by bad management. We used to emphasise hygiene, clean pots, clean irrigation water, no drips from the glass and to always use sterile or sterilised compost. The principle was if you avoid the infection it will be impossible to get the disease. This is the conventional view. It is successfully achieved in commercial horticulture where potent chemical help is at hand.
For most of we ordinary gardeners the water carried spores of this disease are almost everywhere - albeit not in the air. In spite of this I think that the disease will not be a problem if we grow our plants well. I argue that It is impracticable to avoid infection by such things as washing pots, the disease will find another way in. The significant factor is that only If the plant is in a susceptible condition will it succumb to the disease.
Gardeners can do dreadful things to their plants. They sow them too early with excessive artificial heat when there is inadequate light to support them. Some even imagine that small plastic mini greenhouse-like structures standing on a shelf or only slightly better, on a light windowsill in the house, are somehow suitable for seed-propagating plants. Gardeners are advised to cover their seedlings with a sheet of glass, all that humidity, no wonder they get drawn and keel over with rot!
The worst mischief is poor watering, This is a real problem because to the inexperienced gardener it is easy to go wrong. Knowing how much and how often to water is not always obvious. Too much water and high humidity are the conditions where damping-off thrives.
It is not always practicable for certain difficult plants but for all of the many plants I personally grow from seed the germinating seedlings are fully open to the air and I do not cover them. Very high humidity can be fatal. I thoroughly water at first sowing and for very small seed actually water the compost before scattering the seed. For other than very fine seed like antirrhinum I like the compost surface to get quite dry before I thoroughly water again. Damping off really does thrive when it is wet and humid. There will be some infrequent occasions where for very small seed a compost is dry at the surface and yet wet below. In these circumstances a light watering rather than a thorough soak may be in order but not every day!
Some gardeners do not realise that very thin layers of compost lie very wet after drainage and damping off may be more likely to occur.
There are two kinds of person when it comes to our own domestic hygiene. Some are constantly cleaning and every surface is regularly swabbed with some useless anti-bacterial product. Any food falling on the floor goes straight in the bin. Others amongst us are more cavalier and like to keep our immune systems primed. Some people wash pots and others don’t.
|Healthy Corydalis lutea seedlings have ‘volunteered’ in my seed tray of recycled ‘compost’. I have now weeded them out and the germinating seedlings of Dictamnus fraxinella are now doing very well.
|Superb dwarf Lilium formosanum pricei was sown six months ago in my unheated greenhouse. I will have hundreds of dwarf lilies flowering next year.
Sown two years ago, fresh seed of Fritillaria meleagris germinated last February and were grown-on undisturbed in their tray. They are sprouting again.
I have now patched them out on the village plot. The inevitable liverwort has not done any harm.
Addendum, do we have another myth?
Since penning this post six weeks ago I have agonised as to why our students when raising plants in college greenhouses for their plot projects almost always suffered from damping off! (The plants not the students). I have not personally seen the disease since I ‘retired’ from college more than twenty years ago and as this post makes clear my conventional plant hygiene is appalling! (I will however explain in a future post that in some aspects of plant hygiene how I am extremely strict). You will have gathered by now that not only do I not wash pots, I also recycle compost and soil!
I have now remembered that the students, who I hasten to add, were not under my charge, almost invariably covered their glasshouse sown seeds with polythene or glass. I have now seen the light and am certain that covering was the cause of their problem. Instructors ensured the students exerted the most extreme hygiene you could imagine yet the seedlings constantly keeled over.
Plants sown outside in the garden, either by the gardener or nature are almost never covered by anything but soil. You (normally) never get damping off outside. It suddenly dawns on me that covering glasshouse seed with plastic or glass is normal practice for many gardeners. I had somehow cut myself off from such technique and perhaps I have even regarded my own methods as rather more primitive. I now notice in magazines and gardening blogs people envelope seeds with plastic covers much of the time. How strange, I even spotted someone covering brassica seed with a glass sheet!
As is my wont to take things to extremes, for the last six weeks I have tried to get my uncovered seed and seedlings to succumb to damping off. I have watered some more often than normal, some with heavy drenches others with daily light trickles. As usual I frequently fail to find find my rose. Perforce they were unwatered for the five days when we were away. The only watering sin I could not bring myself to do was to leave my seed trays standing in water all day!
Not a seedling has died and I have got healthy seedlings aplenty.
Cathi came round last night and pointed out that I was not a proper scientist and I did not even have the experimental control of actually covering any of my seed! Shame on me but this would have been a bridge too far!