Hardening, Simple yet Effective

The CBE (Center for Bayanihan Economics) continues to apply and demonstrate sustainable agricultural practices that could be shared with the agripreneurs to help them adapt organic-based farm practices. One of the practices is hardening. Hardening is “a treatment that makes the tissues firm to withstand unfavorable environment like low temperature, high temperature and hot dry wind.”
Hardening is a physiological process that is done by slowly exposing the seedlings to unfavorable environment (sunlight and rain) before transplanting in the open field that accumulate the plants more carbohydrate reserves and produce additional cuticle on the leaves. In this process, seedlings are given some artificial shocks before uprooting and transplanting. These shocks include exposure to sunlight, removal of all the shedding nets/polyethylene sheets and minimal variation of irrigation.
Plants grown outdoors are naturally hardened to endure both heat and cold. They can also endure wind and rain because since they are accustomed to it from the start. In contrast, plants grown indoors in containers or greenhouses begin growth in a controlled environment. As seedlings, they experience no rain, wind or significant changes in light or temperature. Once they are transplanted to plots outside, plants are easily stressed and in turn, their growth is delayed. Hardening reduces the impact of the stress of such conditions on plants. Sometimes, it takes several weeks for new transplants to begin growing again, even when hardening is done properly.
The hardening process takes about seven to ten days, depending on the crop variety and climate. The process begins by placing plants outside for two to three hours on a mild day in a shaded location. The following day, plants are placed in the shade for two hours, and move them out into the sun for one hour. By the third day, the plants should be able to tolerate a half day in the sun and the remainder of the day in filtered sunlight or shade. Each time the plants are exposed to outdoor environment, it should be increase exposure to sunlight by an additional hour, while slowly reducing the rate of watering the seedlings. Fertilizer application should be avoided. At night and during extreme weather, seedlings should be brought back inside. By the ninth day, seedlings should be hardened enough to remain outside at night and are ready for transplanting by the tenth day.
References:
http://www.burpee.com/gardenadvicecenter/areas-of-interest/seed-starting/hardening-off-your-seedlings/article10355.html
How to harden off plants
https://www.growveg.com/guides/how-to-harden-off-indoor-sown-plants/
https://www.rhs.org.uk/advice/profile?PID=386
https://www.fix.com/blog/steps-to-harden-seedlings/