1) Skipping starting seeds in flats. We thought we could get away with saving the extra time, but flats are a great idea, and its obvious to us now why they are listed in the instructions of every seed packet. By planting multiple seeds into small-ish pots first, we ended up having crowded seedlings, making it hard, and sad, to separate and destroy some of them. It also became incredibly hard to water with them all so crowded. We had to cut a piece of tubing to pour water through to deeply water each compartment without drenching the foliage.
2) Planting 14 varieties all at once. Maybe we'll try this after we have more experience. Too much to keep track of and worry about.
3) Starting tomatoes, and other heat loving vegetables, way too early. Roger Swain in our Master Gardener course told us to WAIT a few more weeks to plant tomatoes, peppers, etc. We didn't listen, and our greenhouse transplants already hit an almost freezing week. These plants don't like temperatures below 50F, so if you won't have space for them inside as they grow, wait until mid-April to start indoors in our climate (Zone 6), and transplant outside in mid-late May.
4) Using potting soil alone. Although it has produced great results, we are going to try and mix our soilless mixnext time.
What we will do again...
1) Starting seedlings indoors. For very little $$, we were able to set up ideal growing conditions (at least with light) without worrying about pests or other environmental stress.
2) Planting stuff we really really want to eat. Even though the alpine strawberries we planted are TINY and won't provide us with fruit for at least a year, it is something we are looking forward to, and don't mind taking care of while it grows.
3) Redundancy. We finally got around to transplanting the crowded seedlings into larger pots - mainly to end our stress of possibly killing them all if we didn't thin the herd and give them some much needed space. We chose the three strongest plants of each variety for a 1 gallon pot for the greenhouse and small pots to stay indoors. Any additional seedlings we planted directly into the soil. It's like an experiment - some will remain in controlled light and water conditions, others in the semi-controlled conditions of the greenhouse, and some we planted without even worrying about hardening off (the last bit maybe not the best idea, but worth a try).