The weather forecast is suggesting highs in the mid 20s and lows around 10 degrees over the next week. After highs in the low teens and single digit lows this comes as welcome news, especially given the size of the seedlings that are still indoors.
Beginning yesterday we’ve been starting to harden off our pepper, tomato, squash and cucumber seedlings in anticipation of planting. In full transparency we’ve had issues with hardening off vegetables every year so far, but remain hopeful that each experience has provided learnings to limit risk going forward. Seedling hardening issues encountered include:
- Unexpected high winds. Our growing space is on the roof of a multi-story building. While there are raised borders around the rooftop, they are only typical railing height and provide a windbreak for a few feet from the edge. In year one we positioned plants on a quiet morning, and winds picked up quickly, damaging the young plants before we realized the weather had turned.
- Fix: Choose wind-protected areas on the roof, especially early on when transitioning seedlings. Over the days, slowly expose the young plants to increasing amounts of wind up to the levels expected through the summer.
- Significant sun sensitivity. I read about the importance of not leaving young seedlings out in direct sun at the height of the day, but I didn’t appreciate just how sensitive some plants could be. This isn’t about leaving them in direct sunlight all day… it could be about leaving them in filtered sunlight all day, or direct sunlight for a full hour on day 1. These guys are sensitive.
- Fix: In the first few days, be cautious about filtered light. Day 1 we’re using full shade for plants, moving to filtered light and only later to direct sunlight. Similarly, starting with very brief periods of exposure. It’s surprising how little exposure is required on day 1 before your seedlings start to show signs of stress.
- Pests. First year we moved plants from the outdoors back into the room where they originally germinated. This didn’t affect the seedlings themselves, but transported pests into our home. Shortly after we started, we round ourselves with an aphid issue with our houseplants.
- Fix: When not outside, plants being hardened are held in our building stairwell. Fortunately the stairwells in this building have sizeable east and west facing windows, so the plants aren’t in darkness.
That’s it. Take this info not as guidance, but as a one person’s experience and modify as appropriate for your situation. Good luck!