Remedies For Spindly Seedlings

Contributed by Ellen Vande Visse, Good Earth Garden School

Do your seedlings become “leggy”? Here’s what to do.

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You’ll need to carefully manage three factors: lighting, temperature and air movement.  These are crucial for growing sturdy, compact “starts” and bedding plants.  

So you have sown your seed, identified each kind with a marker and have placed your flats in a warm place. You keep the soil moist and wait for germination. Here is the key:  As soon as you see the slightest sprouting, get those emerging plants into the light. What kind of light?  

Windowsill daylight in February and March is not long enough. Nor do incandescent light bulbs provide adequate light. Get seedlings under conventional shop lights - the 4-foot kind with two fluorescent tubes. Set up a “light bank” with a stack of 4-foot-long shelves. Suspend the fixtures by a chain under each shelf. In fact, two sets of shop lights side by side (four tubes total) per 4’ shelf would be even better. 

You don’t need the more expensive full spectrum bulbs. Buy the energy-efficient T-8 fixtures and use 32-watt bulbs. Don’t mix 40-watt and 32-watt bulbs in one shop light.  Pair the right shop light to the right bulbs. You’ll want fresh bulbs every third year, as their light output declines with age. For each shop light, I recommend two different tubes for the best light production. This combination will stimulate strong basic leaf and root growth but not flower development. 

1) 2950 lumens of light output, 20,000 hours of life, 4100 K color temperature and 86 Cri.
2)   2800 lumens of light output, 20,000 hours of life, 3500 K color temperature and 78 Cri.

Your plants need to be under those shop lights for 14-16 hours per day. Use a timer or plug lights in when you arise in the morning and unplug at bedtime. Those tiny leaves must nearly touch the fluorescent tubes to prevent spindly growth. Keep adjusting the suspended shop lights upward as the plants grow. Any seedling farther than an inch or two will not get enough light and will get leggy.

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By April, our daylight is long enough to support your starts, IF you can place the flats in the direct sunlight indoors and IF you can be vigilant not to fry that tender greenery in those south-facing windows. Constantly check soil moisture each day.

Temperature is the second critical factor to prevent leggy-ness:  
Once your seeds have germinated, keep air temperature about 60°F. Coolness keeps the young plants from growing too fast, while warmer temperatures promote sprawl. Thus plants on south windowsills can actually be too hot in the sunlight.  

Air movement is the third critical factor to manage:  
Always provide space between plants for good ventilation. Crowded flats and interlaced plants will trap excess moisture that will encourage disease. Place a fan next to your light bank, turn it on low and leave it on for about 30 minutes every day or every other day.  This artificial breeze will signal your seedlings to resist and stiffen. You are also training them to cope with wind when they move outdoors. 

Congratulations on light, temperature and air management to produce beautifully compact seedlings. Next time: Preparing for outdoor transplanting! 

Ellen Vande Visse operates Good Earth Garden School and offers educational workshops through