Posted: 29/03/2015 at 09:41
I'm afraid it depends on where you are and who is likely to be coming to buy and also whether you have hselter such as a greenhouse or coldframes for growing half-hardy annuals..
I help organise a plant sale every May and one year plants like tomatoes, courgettes and pumpkins can do very well and another year be left sitting there.
I would suggest a mix of annuals and perennials so cosmos, zinnias, French marigolds, larkspur and nicotiana for borders, lobelia and petunias for hanging baskets, achillea, delphinium, lupins and such for perennials. All of these are good, strudy, recognisable plants and easy to care for. If your target market is experienced you could try less common plants.