Vegetable and flower gardens may last year-round in warm regions such as Southern California but don't often survive harsh winter temperatures in colder regions. Gardeners in these cold areas often turn to greenhouse growing to maintain plants through fall and winter, or to grow sensitive plants that won't survive outside. Whether you're planting the greenhouse for the first time or replanting a successful structure, start with cleaning and preparing the soil.
Use a shovel, rake, spade or hoe to dig up the top 6 inches of soil. Remove any rocks, weeds, roots or wood when you turn it up. This ground is inside the greenhouse but is still natural soil where other plants grew at one point. Removing litter eliminates competition, while the digging loosens the soil to allow for root breathing and growth.
Mix quick-draining soil such as sand, loam or peat with organic compost, in equal parts. Lay 4 inches of this mixture on top of your site and mix it into the 6 inches of soil you dug up. The mixture will give all plants good drainage and starting nutrition.
Add fertiliser appropriate to your planting. For vegetable seedlings, use starter fertiliser or 10-10-10. For roses, use rose-specific fertiliser, bone or blood meal, or fish emulsion. Mix the fertiliser into the top inch of soil the day before planting and water the soil with 1 inch of water to help the nutrients sink in.
Replenish soil with the proper amendments at each new planting. Crops deplete the soil's nutrients as they grow, so repeated plantings in the same greenhouse will drain the soil.