Greenhouse light for seeds

[IanW]

I just had a look at some seeds I planted using the baggy method and chucked under the staging in the greenhouse back in July, not expecting too much from them thinking I'd left it too late in the year.

I cannot believe how big they are, presumably from having so much light due to being in the greenhouse vs. those I've had on a table in front a south facing window upstairs. Whilst some are rather red, they are still more mature looking than the ones upstairs and will presumably lose their redness a little now I've got bubble wrap up so they're a little more shaded.

Next year I'll certainly be putting seedlings outside rather than upstairs, it appears to effectively double the growth rate having them in those conditions.

Does artificial lighting give the same kind of boost? I was considering it anyway but I wonder now if perhaps it's worthwhile for all but the sunniest couple of months throughout the year.

As an aside, as I'm planning to keep my greenhouse at a minimum of 10C at the edges scaling to around 15C at the heater is it safe to leave seeds in their humid baggies over winter at these temperatures?

[Vic]

You'd need to provide them with a source of artificial light Ian as our winter days are far too short, I'd expect they'd keep growing at 15C and will become etiolated without sufficient light.

[IanW]

How much harm would that even do to seedlings long term? Would it grow out rather quickly the following year though or is it likely to have longer term effects, like, say, killing them off ?

[Dennis]

Artificial light will certainly give a boost to your seedling but only if it is sufficient wattage. I used a 400w HID for a couple of years and I was getting 5 years growth in one year. For instance one Lophophora came out of the propagator and into a 5cm pot then flowered the following year. Now I use a 200w Eco bulb and growth has slowed right down. Not only is this due to less light but a HID also supplies vast amount of heat as well.

[iann]

Fastest growth comes under long hours of steady moderate light, with steady warmth higher than you would normally have in a house, plus regular water and fertiliser. Of course you have to provide the right levels of light and heat, but this shouldn't be difficult. You can see examples of these plants in B&Q, seed to sales bench in two or three years. I don't grow like this for more than a few months, except for really slow species, then they go into conditions with natural variation. This is easier to manage and the plants then develop an appearance that is more pleasing to me.

The right level of light is quite high, a lot more than you would use for any other purpose. Any discussion is how much light you need must take into account the area of seedlings being covered. A 20W compact fluorescent bulb is more than enough for one tray of seedlings but obviously completely inadequate for a whole greenhouse.

[IanW]

What kind of wattage would you recommend for a 6'x8'?

I'm not sure how to handle lighting or what to get really. I can either rig something up for my table upstairs, stick something to the bottom staging shelf so those on the floor are under it or I can just put a larger light on the roof of the greenhouse itself. Any opinion on what's best?

[iann]

Its pretty tough to light a small greenhouse. They're made of glass and all the light escapes Think in terms of 400W to light the whole greenhouse for starting seeds. Of course that assumes very limited natural light - if the sun comes out you could burn everything. Like I said, tricky.

Just for perspective, your 400W (metal halide I assume) would be nearly 10 times brighter than a standard outdoor security light. Keep the greenhouse warm though

[IanW]

Bubble wrap will at least keep a little light in I guess and I'll only be using the light in the winter after all! I have to consider if it's even worth doing the whole greenhouse though as most the plants being hit by the light will be my main plants not my seedlings. The seedlings are mostly under the benches/on lower shelves where they were safer in the summer. I could leave trays of seedlings in the middle of the floor over winter to get maximum light I guess.

What kind of wattage/size light would I need to cover my 1m x 2m table upstairs? I don't really want to build a case around it and have reflective material inside as the case would block out my window in my room so would just build a frame to hold the light above them.

[RK]

One thing to keep in mind with Metal Halide lights etc.. is the cost of running, there is a very useful cost calculator here :

http://www.ukpower.co.uk/running-costs-elec.asp

Depending on your local energy costs it can get fairly expensive. For me a 400w Metal Halide lamp running 14 hours a day would cost around £24 per month.

I'm thinking about making an indoor setup with a 200 or 400W lamp, or i may just get a few fluorescent tubes instead. In the past i have always sown in the spring which works fine, but i'm curious to see what results can be acheived by sowing in Nov/Dec under lights.