A greenhouse can be a garden's greatest asset: its nucleus and powerhouse. There are many ways of using it and a gardener can adopt one or all of them. In spring, you can start young plants from seed; raise tender perennials to fill gaps in the garden; give young vegetable plants a head start; sow early lettuce while the soil is too sticky to work outdoors. During spring and summer, you can raise greenhouse crops like tomatoes, cucumbers, aubergines...