Hardening off is a technique used when transplanting. As the name suggests, it is the process of letting little seedlings in their protective pots accustom to the harsh, adult world of the garden. Plants do not do well if they change environments immediately and can suffer from transplant shock, which can cause stunted or delayed growth or even death of the plant. Hardening off is an effort to minimize the chances of transplant shock occurring.
The Components of Hardening Off
Hardening off involves progressively exposing your seedlings to the outside weather and withholding water.
Withholding water is best done by gradually reducing the frequency with which you water the seedlings. Some people use a technique where they wait for the seedlings to wilt and then provide water, but this harms growth and is not recommended.
The weather outside involves extremes of both sunlight and cold at night. In the first stages of hardening off, seedlings should be exposed to the sunlight for around 2 or 3 hours. Gradually increase the time spent in the sun until they spent the entire day in the sun.
Similarly, plants need to be gradually exposed to the cold as well. Be wary of frost with plants that dislike it. Just like with exposure to sunlight, begin with 2 or 3 hours and gradually build up by a few hours a day. In the early stages of hardening off it’s vital to protect the plants from any extreme weather conditions such as strong winds, torrential rain or blistering heat.
A simple tip for people that need to go to work/school etc. and can’t monitor their plants constantly is to choose a spot where the plants will receive a few hours of sunlight before being shaded as the sun moves. They can then receive their cold exposure in the early evening before being brought back inside. Change the position in the garden to give them longer periods of sunlight and leave them out for longer to give them longer periods of cold.
When To Begin Hardening off
The hardening off process is best begun around a week to ten days before you plan to transplant your seedlings.