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Leggy seedlings are most often the result of lack of the correct light. The seedling is literally growing up in search of the correct light.
Does your greenhouse get enough natural light? If so, then then polycarbonate may have deteriorated and be preventing the light getting through.
Thanks for the reply Dave.
The greenhouse seems to get enough natural light,it is in a south facing garden with the ridge running north to south.Also it is only 2 years old.
Have i left the top of the seed tray on to long?.Can you take it of when the first sign of germination shows or wait until all the seeds have come through.My tomatoes seem to have come up o.k with no top on the tray,so is the clear top needed when the trays are in a heated greenhouse.
Low light levels are the key factor in leggy seedlings. Too high a nitrogen feed can lead to too much green growth but not really to leggy seedlings. So, given your remarks about the greenhouse then that leaves the cover as you mention. I would definitely take it off as soon as the first few seedlings emerge.
The cover thing has always confused me though, why is it neccessary? I have never used one and it seems to have no adverse affect. Exactly what is it meant to achieve? I have never found a good answer. It can actually have an adverse affect by trapping in moisture and encouraging damping off.
I'll go one further than that, I have worked for the largest plug plant producer in the UK and they don't cover their seed trays. Maybe it's something that is applicable to only a few plants. Possibly they need total dark to germinate. Or maybe it's just an old wives tale. Any views on this?
I now have more questions than answers?HA HA.
I will do some tests on the next batch of seeds to see if they grow better covered or uncovered.I have also thought the same as you on the cover issue,it seems to give the seedlings more chance of dampening off but being a novice I kept to the advice on the various seed packets.
Can you over water the seeds?.I keep mine in a tray of water that keeps the compost damp at all times is this a good or bad way of watering.
Thanks for your time
I'd be very interested to hear the results of your tests, I hope you let us know.
Yes you can over water seedlings, if they are soaked in too much water the roots will not function correctly after a period of time. I would think that standing the pots / trays in water all the time would not be best for them. Let the compost start to dry out (but not completely) then water.