This growing season has been monumental for me: my first full season at the new home, my first time starting seeds in a greenhouse, and the most ambitious garden plans I’ve ever had. While there are many reasons to celebrate, I can’t stop thinking about how I lost all my tomatoes. This hit me hard since tomatoes are the fruit I get most excited about during summer and grow the most varieties of. But gardening mistakes are plentiful, and it’s crucial to reflect on them to learn and improve.
Despite six years of gardening experience, confidence, and muscle memory, I made some beginner mistakes this season in my new greenhouse. For anyone planning to grow in an outdoor greenhouse or new to seed starting, this post is for you.
Temperature
In zone 7, greenhouse temperatures fluctuate wildly. Without A/C or even a fan, I relied on an automatic vent, a screened vent at the base of the greenhouse, and an open door for airflow. Most seeds germinate at 65–85°F, but seedlings don’t thrive in the same heat. After a week of 90°F days and sub-40°F nights, my seedlings were stressed beyond recovery. They became stunted, with thin stems and small leaves—a clear sign of stress.
Transplanting and Soil Mix
I used Winstrip seed trays from Neversink Farms, and they’re easily the best trays I’ve ever used, but they are only meant to be temporary homes. Seed starting trays are too small to support healthy roots for long, and seed starting mixes lack sufficient nutrients post-germination. Leaving my tomato seedlings in their trays was a disaster as they dried out quickly in the greenhouse heat. Maybe I was overwhelmed by the hundreds of other seeds and plants I was growing, but I delayed transplanting them.
Over/Under Watering
Seeds are really incredible structures. They know when the conditions are right for germination, and they have stored within them all the nutrients they need to do it. But after that, it’s up to the gardener. I underestimated the heat in the greenhouse and let my seedlings get too dry between waterings.
Thinning
I densely plant my tomato seeds every season, then separate them into individual plants to sell. This time around, in the greenhouse, those densely packed cells forced the already stressed seedlings to compete for water and nutrients.
Now it’s time to let that shit go. It’s the second week of June and dozens of the plants that I started from seed in the greenhouse are now out in the garden and exploding with colorful flowers and pollinator activity.
