Hill Gardens of Maine - What's Wrong With My Seedlings?

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"What's Wrong With My Seedlings?!"
by Fred Davis, MG, Hill Gardens of Maine (To view other Our Garden Gate articles, click: Archives)

Welcome through Fred's Garden Gate! Like it or not, folks, Spring—and the time to start seeds for our gardens—is upon us! Some time ago someone asked me why their newly-emerged seedlings were tall, spindly and really weak. His description of conditions indicated the seeds were good; the soil (germinating mix) was appropriate; he was growing under fluorescent lights; temperature was adequate and constant; and his tender-loving-care had kept a close watch on his developing seedling-babies.

He's not alone! Hundreds of avid, knowledgeable gardeners all across the country will experience this same set of circumstances this spring - tall, thin, weak seedlings. What's wrong with those seedlings?! Actually, a good deal is wrong.

So, this time, let's take a closer look - and compare germinating conditions in professional nurseries (having greenhouses used to propagate spring plants for "pack" sales) against conditions normally found in the home windowsill or under "grow" lights. But first, let's check out Nature's methods - outdoors.

In our part of the world, ground freezes rock-solid during winter, heaving (loosening) during the spring thaw, then draining-out as ever-brightening sun and gentle breezes draw excess moisture from garden soils. Soils, I might add, that are usually not sterile and not limited to the confines of a small tray or recycled cup. Seeds placed in this unconfined, awakening soil respond to warm daytime and much-cooler night temperatures, recognize conditions as suitable, then almost literally leap out of the ground. Bright (really bright) sunshine bathes young seedlings from dawn to dusk, encouraging them to remain short, compact and quite sturdy. Tiny roots dive deeper and deeper into healthy soil, searching out varying amounts of nutrients - about 60 necessary ones in biologically-alive soils - drawing them in and creating healthy, usually dark green leaves and strong young stems. As rapid growth continues, additional nutrition (fertilizer of one sort or other) is usually added and plants gain strength, appropriate height or length and, eventually, develop flower and fruit. Conditions on a windowsill or beneath fluorescent lights - even the "grow" type - are, however, quite different from those in Nature. And that's where the above-mentioned gardener's problems begin.

Now let's look at conditions in the greenhouses used by professional nursery operators - who, by the way, depend on those tiny, emerging seedlings for much of their livelihood. They are almost always situated in full dawn-to-dusk bright light, enjoying precisely-controlled temperature, humidity and moisture, and utilizing a germinating mix that is little more than peat moss with a little added perlite or vermiculite for drainage and aeration.

Temperatures rise and are controlled at comfortable levels during the day - either naturally or artificially - and are usually reduced after the sun sets. There's a reason for that: plants grow at optimal speed when air and soil are warm; combine that warmth with adequate light, and seedlings remain healthy, short and strong. Allowing that level of continued heat after dark, however, stimulates continued growth. . .but, because there's no light, plants "stretch" long and tall, looking for any source of illumination. Greenhouse pros know that warm days and cooler nights generally result in shorter, stockier plants. They also know that supplemental feeding isn't required - is actually inadvisable - until well after seedlings have developed strong root systems balanced by healthy tops. Adding food too early forces additional stretching - even during cooler nights. It's a delicate balance. . .one that growers strive to match with Nature's more-or-less ideal balance.

So. . .back to our windowsill or "grow" light difficulties. Windows are fixed into one position - they don't rotate to follow the sun. People usually select a window which faces the brightest sun of the day. Between a third and a half of our early spring days are cloudy or overcast. That wouldn't normally be a problem - except that our fixed-position window is already limited to roughly 50% or less of the day's available sunlight. Combine that with widely (oftentimes wildly)-fluctuating temperatures from day to night to day, and it's a formula for poor results - if not failure.

"Grow" lights overcome some of the problems but are frequently under-utilized and poorly managed. The tendency is to assume that this supplemental light is effective at any distance. The gardener above had placed seedling containers about six-inches below his lights. Two inches would be more appropriate for most seedlings. An even more common error is to use conventional fluorescent tubes instead of the full-spectrum type. Not good enough!

Emerging seedlings expect periods of light and dark. . .but the gardener, thinking they need more light so they won't grow too tall and weak, leaves the light on day and night. Seedlings expect "natural" rises and falls in temperature as well. . .but with lights on continuously, temperatures remain almost absolutely steady - warm. The poor babies get the signal to grow (warmth) and "see" a distant source of light (six inches is too far away) and put all their meager energy resources into reaching for the "sky".

Temperature-controlled seed germinating mats add yet another annoying wrinkle to the overall problem. Recall that seeds and seedlings - in nature - expect rises and dips in temperature during the early stages of growth. Gro-mats don't allow those oftentimes desirable fluctuations. Pepper seeds, for example, grown on germination mats are slower to sprout and markedly inconsistent when compared to seeds allowed periodic temperature changes from day to night.

This, sadly, barely scratches the surface of seed-starting. I recommend you obtain a copy of THE NEW SEED STARTER'S HANDBOOK by Nancy Bubel - 385 pages of useful and well-written guidance and reference. Any book store can get it for you. Cost is just under $20 - plus tax if you live in Maine. Whether home gardener and commercial grower, this is one you shouldn't be without.

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