Four tricks to ensure your seedlings get enough light

by Mark Ridsdill Smith on

in FAQs, Featured home page

If you’ve tried starting seeds on a window sill inside, you might have found that they grow thin and weak looking?

If so, this is a common issue, particularly in urban areas. Surrounding buildings or trees cast shade, reducing the light. This creates a problem if you’re trying to raise seedlings inside as they need plenty of light to thrive.

In our new home, I’ve put a table next to the brightest window. But, because the sun is cut out by surrounding walls, it is still too gloomy to raise healthy seedlings. These rocket seedlings are verging on being too thin and spindly – but I’m moving them outside on warm days to give them a dose of bright light. I think they’ll be OK.

Affect of temperature

Seedling growth is also affected by temperature. The warmer your home is, the more light your seedlings will need. So a warm home that is not very bright will be the most challenging to raise healthy seedlings in.

Four ways to get more light to your seedlings

The best strategy depends in part on whether you want to start ‘tender’ or ‘hardy’ crops from seed.
Tender crops include tomatoes, chillies and aubergines – these do not grow well in temperatures below 10 degrees centigrade (50 Fahrenheit) and are killed by frost.
More hardy crops include leafy veg like kale, rocket, and most Asian leaves, root crops like beetroot, turnips and carrots, and peas and broad beans. These can survive colder weather once established, but a hard frost when they are tiny seedlings can be fatal if they are not protected in some way,

1. Wait until it’s warm enough to sow outside

This is the simplest and easiest solution. For the more hardy crops it’s also a very good solution. You can sow these outside about a month later than you could inside – but they’ll still have plenty of time to grow and do well.  This is also a good solution for tender crops like courgettes and runner beans – as these need a shorter growing season than aubergines and chillies. Starting these outside in late April or May is fine. But it’s not so good for tomatoes, aubergines and peppers. If you wait to sow these outside, you may not get a crop at all.

2. Get a small greenhouse or cold frame.

This will enable you to start your seeds a few weeks earlier than you could by sowing them directly outside. For tender crops you should keep an eye on the weather forecast, moving them inside on cold nights.

I found this perspex lid in a skip and made the box to fit. Here I'm growing winter salads in it but I'll also soon use it to keep seedlings protected.

I found this perspex lid in a skip and made the box to fit. Here I’m growing winter salads in it but I’ll also soon use it to keep seedlings protected.

3. Start your seeds inside and move outside on warm days

Moving your seedlings outside – even for a few hours – can dramatically improve their health, as long as the temperature difference is not too great and the seedlings are reasonably well protected. A simple and effective way to protect them is to use a propagator with a plastic lid. This will help insulate the plants from the cold and protect them from the wind. Be selective about which days you move plants outside on, choosing the warmer days. And don’t forget to bring them in again at night!

 

The lid on this propagator is secured with masking tape to help it prevent it blowing off. I learnt the necessity of this when growing on a balcony when the wind would sometimes blow them off into the neighbours garden!

The lid on this propagator is secured with masking tape to help it prevent it blowing off. I learnt the necessity of this when growing on a balcony when the wind would sometimes blow them off into the neighbours garden!

This strategy works really well for the more hardy crops listed above. (It’s my own preferred option). You can also use it successfully for the more tender crops – you just need to be more selective about which days you move your plants outside. Even a few hours of bright light a day will make a difference.

4. Invest in a propagation light.

If you’re serious about growing chillies, peppers and aubergines, you could consider investing in a propagation light. Energy efficient, compact fluorescent bulbs, are now available, delivering the necessary wavelength of light (you want ‘blue light’) for seedlings.

I’m trying one for the first time this year. It’s a bit early to pass judgement but so far the tomato seedlings are doing well.

This is the window where I'm starting the seedlings. It's really too dark so I've rigged a propagation light, under which I'm starting tomatoes and chillies and aubergines. The more hardy crops I'm starting here but then moving outside on warmer days.

This is the window where I’m starting the seedlings. It’s really too dark so I’ve rigged a propagation light, under which I’m starting tomatoes and chillies and aubergines. The more hardy crops I’m starting here but then moving outside on warmer days.

 

Or, you can simply buy the plants

As you’ll have gathered, it’s the tender plants that also need a long growing season, like chillies, that present the greatest challenge. Another excellent solution is simply to buy these as plants later in the year.

Look out for local community plant sales: a great place to buy good value plants and to meet other growers in your community at the same time.

{ 5 comments… read them below or add one }

LBV August 18, 2013 at 8:59 am

Thanks for the swift response

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LBV August 18, 2013 at 4:25 am

Do you leave the light on 24/7 or do you simulate night and day?
Also, would it be beneficial to use an older style of lightbulb that provides heat to start them off (in this case the heat is valuable).

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Mark Ridsdill Smith August 18, 2013 at 8:41 am

This is not something I’m an expert on. But I think that wavelength of light (you want blue I think) is more important than warmth – so choosing a light bulb with the right wavelength is most important. I just leave the light on to simulate night and day – that seems to work fine. There’s more info on Wikipedia here:http://en.wikipedia.org/wiki/Grow_light

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Emma April 9, 2013 at 8:29 am

You can also pop you seedlings into a cut away box that has been lined with foil – so light coming in at the front is reflected back. It’s a low cost option and helps seedlings grow much straighter.

Reply

Mark RS April 9, 2013 at 9:07 am

Hi Emma, that’s a great tip, and one I forgot to mention – so thanks very much for posting it on here. Also, some cartons (fruit juices sometimes?) come lined with reflective foil and I’ve seen people cut them open and use the back as a reflector in a similar way. Wish I knew which products came with this reflective foil, any ideas?

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