What to Plant During the Fall in Greenhouses

Bulbs

• Fall is the natural time to plant bulbs in the ground, but save a few to plant in the greenhouse. Bulbs planted in a greenhouse will flower sooner than those planted outside and are often taller since they are protected from the weather extremes. Plant iris, Acidanthera, anemone and Triteleia in the greenhouse in fall for late winter or spring blooms. The greenhouse is also an ideal place to sow flower bulb seeds. Bulbs grown from seed take a while to fully develop. When you start them and grow them on to maturity in a greenhouse, you have more control over the situation than if you directly sowed them in the garden.

Annuals

• Annual flowers are a great way to add color and fragrance to the winter greenhouse. An annual is a plant that grows, flowers, sets seed and dies in one growing season. September is an ideal month for sowing seeds of stocks, which should bloom in time for Valentine's Day. Sow seeds of larkspur, snapdragons, alyssum, bachelor's buttons and winter flowering sweet peas in October in the greenhouse. Sow pansy and viola seeds in November. When selecting annuals to plant in the fall, consider the lowest minimal temperature in your greenhouse during the winter and choose flowers that are able to tolerate these temperatures.

Vegetables

• There is no limit to the types of vegetables you can plant in fall in a greenhouse, but do consider how cold your greenhouse will get over winter. Some vegetables will not thrive once the temperatures fall below 50 degrees Fahrenheit. Start out by sowing seeds of warm-weather crops such as peppers, tomatoes, eggplants and melons. These heat-loving plants will grow faster in early fall when the temperatures inside a greenhouse are warmer and easier to maintain. Then sow seeds of cool weather crops once the temperatures begin to cool down. Lettuce, spinach, radish, broccoli, cauliflower and carrots are ideal choices. Even if your heater fails, most cold-weather crops will survive.

Perennials

• Fall is an ideal time for sowing perennial seed because it often tricks the plant into blooming sooner than it would if the seeds were sown in the spring. Perennial plants tolerate much lower temperatures than most other plants, meaning you can save money on your heating bill while still having something green and growing to enjoy. September is an ideal month to plant delphiniums, Oriental poppies, Sweet William and daisies. Sow perennial sweet pea flower seed in November. Select which perennial seeds to sow based on the length of time they take to germinate and the amount of time they take to flower. Sow the seeds with the highest numbers first.