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germination lessons

March 26, 2011
touchstone beets

in early spring, the greenhouse is where all the action is on the farm. the soil in the fields is still too wet to work, and the weather is all over the place (highs in the 60’s last week, then thunderstorms, then snow and lows in the 20’s this week). but while we wait for spring to really happen, we get a head start on the season inside our big clear plastic house. the greenhouse lets in the light our baby plants need to grow, protects them from wind and snow, and traps the solar heat inside an inflated double layer of plastic. we also have a propane heater to keep the temperature up at night, and on days when the sun is obscured by clouds. the first seeds were planted about a month ago (onions on 2/28), and at least once a week since then a new set of trays has been filled with soil, populated with seeds, sprinkled with vermiculite and watered. and then, each tray goes into the germination chamber.

germination — that magical transformation of a seed into a tiny plant — is a delicate process, and each species has its own way of going about it. rosemary and several other herbs germinate best when exposed to light, while most vegetables do better when covered lightly with soil. the soil around carrot seeds need to stay moist for up to 2 weeks while they take their time to sprout — and carrots hate to be transplanted, so they don’t even make an appearance in the greenhouse. verbena, on the other hand, needs the soil to dry out completely before it is watered again.

germination guide

germination guide from johnny's seed catalog

temperature is another key factor in germination. each crop has a minimum temperature below which no seeds will germinate (around 35 F for onions, 40 for parsley, 50 for tomatoes and 60 for beans). as temperatures rise above that minimum, the percentage of seeds that germinate increases up to an optimum temperature (between 70-95 F for most crops). above the optimum, the percent germination declines again, until a maximum temperature above which no seed will germinate.

since our greenhouse generally is in the range of 60-75 degrees (the heater is set to 60, but the exhaust fan doesn’t start moving hot air out til it gets to 75), we are above the minimum for our crops to germinate, but not hitting the optimum temperature for most of them. so that’s where the germination chamber comes in.

germination chamberthe germination chamber is just a warmer container, usually with racks or shelves, where growers place sown flats for a few days to speed up and increase germination. ours is basically a bakery rack outfitted with insulation, a plastic door, and an uncovered crockpot, which keeps it both warmer and moister than the rest of the greenhouse. by turning the crockpot to “high” at night, and “low” on sunny days, as well as venting or closing the door as needed, we can keep it consistently 80-85 degrees inside.

because of the insulation on all sides but the one with the door, the germination chamber is fairly — thinside the germination chamberough not completely — dark. as long as the seeds have not germinated, this presents no problem. but within hours of when they sprout, seedlings start to strain for any hint of light. so if you leave the trays in too long, the plants grow too tall, too quickly to support their own weight once they get larger. but if you take them out too soon, you negate the benefits of the germination chamber by dropping the soil temperature before the seeds have a chance to germinate. so it’s a delicate balance, and since this is my first year working with a germination chamber, i’m still learning.

last monday, i sowed eight flats of cabbage and put them in the germination chamber. i checked them several times on tuesday, but saw no changes. on wednesday morning, i peeked in and saw a few cotyledons emerging from one of the trays. i pulled it out, and confirmed that a number of the seeds were sprouting, so i put the tray on the bench and proceeded to take the other seven cabbage trays out without close examination.

two cabbage traysafter a few days, i noticed that there was a significant difference between one tray of cabbage and the others. in one tray (the one on the right in the photo), the cotyledons were large, healthy and uniform. in most of the other seven trays, the cotyledons were much smaller, and the germination was much more variable.

in talking to my mentor farmer, i learned that the temperature varies in different areas of the germination chamber, so even though 2 trays are the same crop variety, they may not start germinating at the same time. since then, i have been careful to check each individual tray before moving it out to the greenhouse benches.

having learned last week the effect of prematurely removing trays, this week i got to see what happens when you wait too long. on monday, i planted lettuce, yakina savoy, and spinach. (the spinach did not go in the germination chamber since it prefers cooler temperatures for germination.) on wednesday, i thought the lettuce and yakina savoy would germinate, but still no sign of sprouting by the end of the day. however, thursday morning, many of the cotyledons were already up, too tall and leaning toward the light of the door. two days later, outside the germination chamber in full sun, they’re still leaning. a few more days will show whether they’ll grow out of it. if not, i’ll be planting all those seeds again.

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