This chart below is based on the weather in Southeast Pennsylvania, so it includes Conshohocken Community Garden. Notice that yellow means plant seeds outdoors or transplant plants outdoors and green means harvest. If there is orange, they suggest to start from seedlings grown indoors (or buy seedlings).
We have grown plenty of things successfully from seeds in the ground in Conshohocken Community Garden where the conventional wisdom is to have seedlings.
Whatever you like or want to try, get planting some things (though be careful with tomatoes and watermelon and other warm weather plants – wait till mid May). We hope this helps you.
Conshohocken is USDA zone 7a.