January Seedlings!

Dear Martin

I wonder if you can give me some advice on growing lights please?  I want to grow plants from seed, but have no greenhouse only a garage which has little natural light. 
I think maybe growing lights would be the answer, but wonder whether plants started off in this way will then continue to need light and warmth until time to plant in the garden;  for example sweet pea seedlings.

If I were to plant seeds in January, how long could I keep them under such conditions, would the seedlings bolt if left under growing lights for too long? I do have a heated propagation mat.
I find Seedlings grow spindly if left on window sills in the house. 

Many thanks,
Julie Davison


Dear Julie

Many thanks for your recent request for advice on growing lights to help with the propagation and growth plant at this dull time of year when sunlight is at a premium.

To germinate and raise young plants successfully in the winter months of January and February and avoid the spindly, leggy specimens you’ve raised on the windowsill in the past, Grow Lights are really the only answer. The reason seedlings without the benefits of artificial light grow tall and weak – commonly known as ‘leggy’ - is due to natural winter light; or more accurately the light quality and lack of it. Because the days are shorter this time of year and on the few occasions the sun does shine, the intensity of the light is not as it is in the spring and summer, so the plants grow tall and pale as they search for more light to enable them to photosynthesise and grow. It’s a little like what happens when you force rhubarb but nowhere near as extreme!
When using the Grow Lights, there is no strict lighting regime you need to adhere too (unlike the commercial practice of raising cut flower crops such as chrysanthemums) but plants will plants rarely benefit from receiving daylight over 18 hours. It’s also impossible to ‘overdose;’ the plants on light but given the previous statement, it wouldn’t make economical sense to keep the lights on constantly.
It’s good practice to use the Grow Lights in the morning and evening of bright sunny days to supplement the natural daylight, and the kit could be run off a timer to help illuminate overcast conditions. An 18 hour burst of light per day should be enough for propagation purposes and it’s probably worthwhile placing some plants out of the reach of the light to see how their growth contrasts of those under the bulbs. The bulbs we supply are 6400K rated, giving the correct spectrum of light to propagate and grow on young plants. A special bulb to promote flowering (2700K) is also available - the ‘K’ stands for Kelvin, a measurement of colour temperature.
In practice, the sweet pea seeds you mention growing could be germinated anytime now under the lights and then place in an unheated cold frame for planting out as early as March. They’ll tolerate light frosts so as soon as the soil is pliable, get them out of the cold frame and into the garden!  
I do hope this information will prove to be of help; as always, please contact me if you have any further questions and the best of luck with your light-induced propagating and growing.