Growing plants in a natural greenhouse is similar in many ways to growing plants in a commercial one. Differences relate to the choices made about growth regulators, seed varieties, growing medium, fertilizers, and pest and disease control methods used.
One of the most important differences is that natural greenhouses do not use growth regulators, while commercial greenhouses often do. Growth regulators are used to control plant size, growth rate, and onset of blooms. Before flowering plants are shipped to stores, additional chemical regulators may be applied to slow growth rate and provide a longer sales period. Plant growth is slowed until the chemicals wear off several weeks later.
In a natural greenhouse, plants are allowed to grow at their optimum rate, outperforming most plants raised with growth regulators. To provide a continuous supply of young, healthy plants, seeds are planted in succession. Successive plantings are watered and fertilized regularly to meet the particular needs of each group of plants. This results in healthier and more productive plants, especially important to people who grow vegetable gardens and want well filled out flower beds. This critical difference in plant quality is one of the main reasons customers will return to buy plants that are grown naturally. When growing plants for your own business, increased productivity increases profit. In the photo, flats of alyssum, which grow quickly, were planted each week, while flats of basil, which grow more slowly, were planted two weeks apart.
The garden-planting season spans several months. Some customers will plant annuals first and then continue to plant perennial flowers and herbs through July and August. Weather will speed up or delay the planting season and customers’ personal responsibilities will determine when they can plant. A steady supply of healthy vegetable, herb, and flower plants, annuals and perennials, are needed from early spring through late summer. Successive germination can also be used for your own plants. Those needed to produce tomatoes early in the greenhouse can be started in January or February, while plants for outside production will need to be started later in March or April.
It is illegal for greenhouses to apply growth regulators to vegetable plants, but they will become root bound when they remain in their containers too long. Younger plants will outgrow older root-bound plants and usually out produce them because plants recover slowly once they become root bound.
The best way to provide a continuous supply of healthy plants over the planting season is to germinate them in succession. Planning for successive plantings is quite easy.
- List the total number of flats of each variety you want to sell and use during the season.
- Select one variety. Determine the number of flats of that variety you want to sell or plant on the earliest date.
- Locate the recommended length of time from seed to sale on the seed package or in the catalog.
- From the sale or planting date, count back the number of days or weeks required.
- Record the date seeds need to be started.
- For each successive planting determine the next target date, usually seven to fourteen days later.
- Repeat steps 2 – 6 for each variety.
When germinating several varieties on several different dates, you will need to write down each date on a schedule or calendar. Remembering dates for several varieties is very difficult, but your germination schedule will remind you when it is time to plant each flat. Planting in succession spreads seeding of flats over a longer period and may reduce or eliminate the need for employees.
Vegetable plants are grown in succession, providing new batches of plants every one or two weeks. [In southeastern Ohio, the frost-free date is usually between May 15 and May 22. You will need to adjust your dates to fit the growing season in your area.] For lettuce, broccoli, cabbage, and other frost-hardy plants, I germinate the first flats so they will be ready to sell about April 20. Additional flats are seeded every seven to ten days so the last batch will be ready to sell by the end of May. For tomatoes, peppers, eggplant, basil, and other main season crops, I plant every two weeks so that the first batch is ready to sell in early May and the last batch in the middle of June. The first cucumber, melon, winter squash, and pumpkin plants are not ready to transplant until mid-May because they need warmer soil than most other vegetables. Because they grow so fast, I replant once a week for about four weeks.
The number of flats at each planting varies, seeding fewer flats for early and late plantings and more flats per variety for the heavier planting periods, which tend to be in the middle of the planting season. Vegetable plants, grown for early crops in the greenhouse, are started even earlier, using the same planning process discussed above.
Since lettuce, broccoli, tomatoes, peppers, and vining plants all grow at different rates, it is necessary to consider those rates when planting the seeds. Lettuce, cucumbers, pumpkins, and melons need about four weeks from seed to sale; broccoli and tomatoes, eight weeks; and peppers, ten weeks.
I also plant many annual flowers in succession. The most popular varieties are germinated one or two weeks apart for up to six weeks, while less popular varieties may be planted in only two batches for early and mid-season.
Some varieties must be planted later than the seed package recommends when used for bedding plants. Tall varieties of zinnias, cosmos, and dahlias, for example, grow tall too quickly for pack sales. Flats can be seeded weekly and sold before they bloom. That is necessary because chemical regulators are not used to control height or force early blooming while plants are still smaller. Since the green plants are full and healthy, adding signs with pictures of the plants in bloom motivates many customers to buy them. To sell them in bloom, they can be germinated earlier and transplanted into larger pots for sale as larger plants. Plugs raised for hanging baskets also will need to be planted several weeks earlier than those sold for bedding plants.
The health of plants in a natural greenhouse can also be improved by choosing disease-resistant seed varieties, a weed-free growing medium, the right fertilizer, and pest control products with low or no toxicity. Information on these topics is available in The Natural Greenhouse: Growing Plants and Food for Profit.
Gini Coover is the author of The Natural Greenhouse, Growing Plants and Food for Profit. She has grown greenhouse plants and vegetables for twenty-six years, selling retail and wholesale from her greenhouse and at the Athens (Ohio) Farmers’ Market.