Hardening off

  • Frederick Yaffe
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08 Mar 2017 18:57 #20 by Frederick Yaffe
Frederick Yaffe created the topic: Hardening off

With the outdoor season upon us, acclimating soft plants becomes important again.
Those of us who take cuttings always work against the softening effect of moving the unrooted cutting from the bright light under which we grow the stock, to the subdued light and elevated humidity under which we root the clone. You can germinate seedlings in much the same conditions in which you intend to grow them, But with rooted cuttings, (Clones), this is different. We are faced with a transplant that has spent maybe a few weeks in the propagation bed or cloner, treated with barely enough light for survival, and became accustomed to 100% humidity, misted, prayed over.
So it is crucial to shorten the rooting phase. The sooner the clone comes out, the fewer undesirable changes take place, resulting in better survival and take-off. It is the step-wise restoring to the more intense light, etc., that creates the most problems. The best-fed clones, from the brightest-lit mothers and most well-prepared cuttings do the best. They need to be collected in a baggie with a damp paper towel, kept misted until "stuck", and shielded from direct light(some experimenting needs to be done), and held in a greenhouse-like atmosphere. The unstressed clone will not wilt, will not lose color, and will not even know it has been through surgery.
The clone will go through stages, and one can begin to back off on the humidity and brighten the light before roots emerge, occasionally misting with dilute foliar feed as rootlets begin to show. Swapping out the clone to a baggie or a hardening-off dome which we leave open somewhat will allow it to harden a little is the first step. Always be aware of the tendency for the air in the baggie, or under the dome to heat up; we want the air to be about the same temp. as the media. around room temperature. Placing a small thermometer in with the clones is a good idea, be sure it's clean. Don't let the media dry out, but don't overwater. Some folks tape down the dome to seal it, but I prefer to inspect often, looking for yellowing leaves or Botrytis, (the cottony grey mold) to remove. Mist after each opening, look for condensation the dome interior, if none,apply some. Don't let the dome drain back into the tray. Clones may elongate during propagation, this is your early sign that the "slip" is acclimating, and it then it is possible to back off on the humidity and brighten the lights a little bit without harm. Mist frequently, and less often as you go. Commercial propagators using intermittent mist will dial back the frequency and duration of the mist on a schedule like "third day every 30 minutes for 15 seconds, fifth day once an hour for ten seconds" etc, always watching the weather. No mist on rainy days in a greenhouse is seen, depending on the crop. Growers using domes with valves can adjust accordingly, a nice feature.
Always watch for signs of stress, tip curling, leaf cupping, loss of sheen, etc. Take advantage ambient humidity spikes on rainy days, etc., to remove some support. A layer of newspaper,dampened, can be laid atop the cuttings to accomplish some of these transitions.Mist the paper to provide humidity. Lower temps. as the process unfolds. So we are gradually taking away the supports as the clone gains the ability to support itself. When roots begin to emerge, and tip growth resumes, this is getting near too long in the propagator. Putting your work outside for a half hour in broken shade or dappled sun will begin the climb to full sun and air. Increase exposure daily. Be very careful not to over harden,and provide feed and water as needed to avoid this. Inspect roots often, if chlorosis occurs, ( lightening of the green color,emerald green is good), foliar feed and fertilize at 1/4 strength. If you see salt deposits on the leaves, rinse w/ clerawater, don't overwater.
Give to material a good shake or stroking to keep from stretching,and grow on at 65 to 80 F. Use higher temps at night(darkness)than day to help avoid stretching. Foliar feed will leave deposits on the leaves; rinse this off, shake it out gently, don't saturate the media as you do so. Foliar feed allows one to grow with less salt in the media, good for the roots to be in low osmotic pull environment. Provide air movement, gradually hope to see the foliage shivering,
If all goes well, the lowermost leaves will neither turn yellow, or fall. Hopefully, one then thins the canopy to admit light to the center and improve circulation.

Next, we will describe a simple misting system with bottom heat, using nutrient mist, the gold standard for rooting cuttings, from simple, found parts, and a little Home Depot. No timer will be used, called an "electronic leaf".

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