don’t skimp on light when starting seeds

plant lights 2STARTING SEEDS is not hard…unless you skimp on light, or your timing is off. Sorry, friends, but your windowsills just won’t do, and over-eager “headstarts” usually result in past-their-prime seedlings.

For the timing, consult my Seed-Starting Calculator, customizable to your own location according to final frost date. But first…

I recommend investing in a reflective hood that houses high-output fluorescent tubes called T5’s, or T5 HO’s. I can’t wait until LEDs for seed-starting get a little farther along in development, and the prices come way down, since LEDs will put out even more light with less heat. (But good news there: It’s progressing fast, and there are even LED tubes engineered to fit into our T5 hoods, so only the bulbs will need replacing.) Meantime, T5’s are a big step up from old-style fluorescents, which I have stopped using–providing up to eight times the light (more energy efficiently, too).

outdoor light in springHow many flats will you have under lights at any one time? Remember: No need for supplemental light before seeds sprout, and once weather begins to stabilize, you can carry seedlings out by day to enjoy natural light, as I do. That produces stronger plants; the illustration (with data from plant physiologist Dr. Thomas Bjorkman of Cornell) shows why, since no artificial lights can match nature, even on a cloudy spring day. It also saves lighted space indoors.

My biggest gridlock is late April, when my cool-season crops (like some Brassicas) are in their last week or two inside, and my warm-season ones (like tomatoes) have just sprouted, needing light as well. Nevertheless, I get by with lights to accommodate about three flats at any time—again, because I move things outside to a sheltered bright spot on stable weather days. Standard commercial seedling flats are 21×11 inches, if that helps the calculation of how much hood you need; many home garden seed-starting “kits” have a slightly smaller footprint.

Adjustable T-5 grow-light hood and standRather than one big hood, I have two smaller ones–one suspending a 4-bulbs T5 reflective hood that holds a single flat (above), and another for two flats. The modular arrangement allows me to economize on energy use when I only have one flat going.

Important note: Many hoods do not come with a “stand”–or with height-adjusting hardware, to keep lights close to growing plants. Use chain and S-hooks, for example, or special pulley-like hardware made for the purpose and used in hydroponics; some carpentry skills required. Examples of hoods for one to four flats, requiring a little carpentry and not, are featured at this link.

more help with seed-starting

(Disclosure: Purchases from Amazon affiliate links yield a small commission.)

  1. Laurie says:

    Thank you for these excellent growing tips. I have grown lanky seedlings in the past, so the dates will help and I will also check out the lighting. The year I began taking the seedlings outdoors for the day made a huge difference as well. I am sharing this post with those who have been asking about planting dates. Thanks again!

  2. KarenJ says:

    Agree with you – light and not starting too early are two of the keys.

    I’ve got a biiig south window, which is in addition to my plain old florescent fixtures. During this time of year the sun pours in, especially in the morning. By the time the sun moves north, it’s usually time to move some out to the hardening-off area, although a hard freeze will make me drag them back in…

  3. Bibby Moore says:

    I have used the T5 four foot with 6 bulbs for 4 years
    I move seedlings out to back deck and also have built plastic covered chicken wire houses to put over them on the deck so I don’t have to carry them all in St night
    Sometimes have had 10 flats of seedlings as I share plants with friends. Am 72 this year do might take a break a buy plants at our great farmer’s market.

  4. Beverly, zone 6, eastern PA says:

    I was wrestling most of today with additional hanging light set ups in anticipation of extra seedlings and cuttings. I do not have the T5’s yet, more’s the pity. I do use warm and cool fluorescents in each fixture.

    I also favor moving flats outside and back in to give them a shot of *REAL* light and some moving air. I have several cold frames to help me during very early spring when full-to-bursting flats intersect with frosty nights and overcrowded growing space inside. Knowing how to juggle all these requirements can make a gardener clever and resourceful.

    1. margaret says:

      Well-said, Beverly! I think the outdoor treatment is how I got away with even wimpier old0style lights all those years. :)

  5. Kevin W. Byrne says:

    T 8 & T 12 bulbs need to bee 5,000K and 2600L or higher for seed starting, Mine
    work good ant the cost is lower for fixtures also, home made stand out of wood,
    two fixtures @ 4 bulbs total @ four flats underneath for my garden. You have a nice post worth reading whenever it arrives in my internet site. Thanks

  6. Rose says:

    In response to Judy Walther’s question… No, the T5 lights don’t fit in regular fluorescent fixtures. Too bad because I have old shop light fixtures with grow lights in every room around the house during seed starting season. I bought a T5 set up last year and used it side-by-side with old fixtures fitted with new grow light bulbs. The T5’s gave dramatically better results in terms of plant appearance and vigor for all the annuals, perennials and vegetable seeds I planted. Well worth the price for the T5. I’m retired and have the time and patience to start duplicate seeds for such comparisons. :-)

    1. Judy Walther says:

      Thanks Rose.I’m going to pull the trigger and order a new setup today. I’ll be anxious to see the difference as I have used fluorescents for many years.

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