Hardening off

Hardening off is the process of gradually acclimating seedlings that were started indoors, or bought from a sheltered greenhouse, to outdoor conditions such as direct sun, wind, temperature swings and lower humidity, before they are planted into their final balcony containers. Seedlings moved outdoors abruptly can suffer sunburn, wind damage or transplant shock, even if the weather itself is mild.

The process typically takes one to two weeks, starting with an hour or two of sheltered, indirect outdoor exposure and gradually increasing both the time outside and the amount of direct sun and wind the seedlings face each day. Bringing plants back inside or under cover overnight in the early stages protects them while they adjust, and skipping straight to a full day outside undoes much of the benefit.

When hardening off on a balcony, a partly shaded corner away from strong wind makes a useful transition spot before plants go into their final full-sun location. A common mistake is hardening off too quickly during a warm stretch and then having plants set back hard by a sudden gust of wind or a cooler night, so watching the forecast during this period matters as much as the daily schedule.