There are self inflicted difficulties associated with growing tomatoes. For me that would be my inability to put leftover seeds in the fridge and just leave them there till next spring. I just have to keep planting them. (Hmm – seems that chocolate/fridge reflex got me into bad habits!)
Non self inflicted difficulties would be those associated with plant disease. Or can these also be prevented? The disease most relevant to my current immersion in seeds and seedlings appears to be Damping off Disease. So to distract me from further seed sowing or Malteser munching I’ve decided to research it in more depth.
This is what I found out (and yes all the talk of spores and fungi was enough to take the edge off my appetite and make me do a mental check as to the last time I had investigated the far reaches of the salad drawer).
It’s a generic term for several different types of fungal diseases which attack and cause seeds or seedlings (not just tomatoes) to die.
The disease is found in soil and water but once spores develop they spread by air.
When does Damping off occur?
At three possible stages.
- Seed rot. Infected water in the compost enters the seed capsule and kills the seed before it is able to germinate.
- Pre emergent. The seed has sprouted but is still beneath the surface of the compost. If infected now no seedling will emerge.
- Post emergent. The seedling has emerged and maybe anything up to 5 cm tall. If infected now the seedling will collapse when the root or lower stem becomes infected and rots.
At 4 weeks plus the stems of the young plants should be tough enough for the danger of Damping off to have passed.
Where does Damping off come from?
The disease is present in soil or water. So places it’s likely to be lurking in the context of tomato growing are:
- Sowing containers i.e. seed trays, pots, even labels. I thought new containers would be fine as they’ve yet to come into contact with soil or water but I’ve now read a garden centre environment can be enough for contamination to take place. (I’m hoping this is alarmist!)
- Sowing compost. Again I bought new but have read that fresh from the bag is not the same as sterile.
- Water. Water from the mains (tepid not cold!) is fine. The risk is in collected rain water.
What triggers Damping off?
It’s a fungal disease so all the yucky conditions that spores thrive inwith an emphasis on dark, wet and humid! Lack of ventilation/air circulation is also a cause.
So in the context of tomato growing triggers would be:
- Over watering . If compost and seeds/seedlings are waterlogged, air/oxygen are unable to circulate.
- Excessive humidity in a propagator or greenhouse.
Too many seedlings in one container. Overcrowding means air doesn’t circulate round the seedlings AND that’s it’s easy for the disease to spread.
- Low or poor lighting levels.
What can be done to prevent Damping off ?
Hospital standards as laid down by matron!
- Clean and disinfect containers before use and if using one, the same for the greenhouse.
- Water with clean mains water.
- Use fresh and sterile soil (tips for sterilizing soil include heating in the oven at 150c for an hour or at full blast in the microwave for 6 minutes).
- Sow seeds sparsely.
- Sow the seeds on the compost and then rather than covering with more compost, cover with matter that is less likely to retain moisture like sand or perlite (this is causing me confusion re Vermiculite which I used because it did retain moisture – but perhaps thinking of it’s odd consistency it’s virtue lies in being good at retaining moisture and allowing air to circulate).
- When seedlings are ready, thin out to allow air to circulate round the stems.
- Create a gentle breeze around (not directly at) the seedlings with an electric fan.
- Let the surface of the soil dry out between waterings.
- Water from the bottom up.
- Provide a light bright sunny location.
I’ve also read you should take preventative action by watering the compost/seeds with a soluble copper based fungicide. The two that get the most name checks are Cheshunt compound and Murphy Traditional copper fungicide. Cheshunt compound contains copper sulphate and ammonium carbonate, Murphy’s Traditional contains copper oxychloride. For knowing which I am now a tad better informed!
I also came across natural approaches to prevention. These included clove or chamomile tea used to spritz the plants, cinnamon sprinkled on the compost and garlic cloves crushed to either mix with water to spritz or as a soak for the seeds prior to sowing.
I haven’t used either the copper based or the natural solutions so would be interested to hear what you’ve tried and would recommend.
What happens if your seedlings do get Damping off ?
Cheshunt compound or Murphy traditional copper fungicide get mentions here as well in that they can be applied and used to protect the seedlings not yet affected. However for the seedlings that have the disease it would appear that they can’t be saved and so need to be removed and disposed of along with the compost. If containers are not disposable they must be disinfected.
I am keeping my fingers crossed that all this remains theory and not practice!
However my research makes me question if I should have taken preventative measures (either chemical or natural) at the start of the sowing process. When I was reading up on how to sow tomato seeds I didn’t come across many mentions of this step. It was only when I started researching Damping off itself that it cropped up as part of the process.
I was also struck by how many mentions air circulation and goodventilation got as part of the preventative process. This had come up in the advice I’d read on how to sow seeds and care for seedlings but I hadn’t quite appreciated how important it was. With plants my tendency is to consider light and water but not so much air. So understanding Damping off has helped me understand the importance of this 3rd critical element.
To get a better understanding yet, hearing your approach to prevention and your thoughts on sterilising soil, the use of fans for air circulation and on disinfecting even new containers would be great.
The one good thing about doing all of the above is that it makes defrosting the fridge seem like a walk in the park!
Photo by Chris Fleming