For more than 10 years, growers at Four Star Greenhouse in Carleton, Mich., have finished many spring crops outdoors, beginning in early April, with tremendous success. A wide array of container crops are finished outdoors, including 4.5-quart, 1-gallon and 13-, 18-, 10- and 12-inch containers and hanging baskets.
Four Star feels its spring crops grown outdoors produce a high-quality finished container that can equal or rival those grown indoors, no matter how high tech and high quality the greenhouse structure may be. With the higher light levels, cooler temperatures and natural air movement provided by the outdoor areas, plants specifically selected for growing outdoors tend to finish fuller, tighter and have better branching and higher bud counts than identical containers grown in the greenhouse.
A Little More Roomy
By using these outdoor areas for growing on crops, not only is quality maintained, or in many cases improved, but also additional growing space is created indoors for extra production in peak weeks–and multiple crop turns are easier to achieve. Four Star plans finished crops every two weeks from early spring throughout the summer and into the fall. With the additional use of its outdoor areas, this plan is met without quality being compromised. When using outdoor areas, a grower has the option of either growing and shipping directly from outdoors, or bringing crops back into the greenhouse for fast finishing in space created from earlier shipping. The procedures for using outdoor finishing areas are rather simple, with acceptable risk levels, if the recommended guidelines are followed.
Growing areas can be unused areas of a parking lot, raised benches outdoors or rocked/weed mat-covered areas directly on the ground. Fundamentally, any outdoor location can be used.
Frost and Freeze Protection
Frost/freeze protection must be provided. It has been noted many times at Four Star that selected crops will survive quite well when exposed to extended temperature periods into the mid-20s. What has been seen on occasions in the past is the negative effect of severe frosts on these same selected crops. Under severe frost conditions, crops that will withstand a severe freeze without frost can suffer from tissue burn and/or flower loss. Measures that have been successfully used for preventing frost/freeze damage are the use of frost cloths or sprinkler systems. Generally, there are three grades of frost cloths offered by suppliers, and growers should purchase the grade that best matches the severity of their historical frosts.
When considering the use of frost cloths, growers should also evaluate the labor requirements involved in placing and removing the cloths. Also, it’s best to place the cloth over, but not in direct contact with, the crops due to the possibility of tissue damage from the direct contact. Many growers design a hoop system above the crop for ease of cloth pulling and additional plant protection.
Crops have been divided into three select groups for moving outdoors. This grouping is done based on past performance outdoors in Southeast Michigan and must be evaluated at each individual grower’s location before implementing. Proven Winners varieties are listed, but other genetics should generally fall into the same listing.
Group 1–Normally moved outdoors in early April: argyranthemums, Symphony osteospermum, Supertunia/Surfinia petunias, and Babylon verbena.
Group 2 - Normally moved outdoors in mid to late April: Superbells and Million Bells calibrachoa, Flying Colors diascia, and Safari and Innocence nemesia varieties.
Group 3–Moved outdoors usually in early May: Sundaze bracteantha, Laguna lobelia, Solaire and Peters Gold Carpet bidens, Sunsatia nemesia, Soprano osteospermum, and Superbena and Tukana verbena varieties.
Trials should be run to protect against individual varietal sensitivities. An example of varietal sensitivity is Supertunia ‘Mini Strawberry Pink Vein,’ ‘Mini Rose Vein,’ ‘Bordeaux’ and ‘Citrus,’ which should all be kept indoors and moved out with Group 3 due to sensitivity to extreme cold.
We have determined that it is best to plant each crop indoors, grow indoors for two weeks to establish a good root system and then move outdoors. This method eliminates losses that are sometimes seen from planting and moving directly outdoors. However, there are growers who plant and grow directly outdoors successfully. Growers should consider and trial both options for determining the best method for their applications. Four Star typically moves half of its first two or three crops outdoors and keeps the remaining half indoors to ensure accurate finishing dates. To best use space, these two crops within a crop are laid down in separate areas so that when all material is picked up for moving outdoors, one large open growing area is created instead of smaller areas spread randomly throughout a greenhouse.
When preparing to move crops outdoors from the greenhouse, there are a number of steps that can be taken to ease the transition of environments. If possible, two days before moving outdoors, greenhouse temperatures can be lowered to 45 to 50°F for toning the plants in advance of the move. This may not be possible due to younger crops or more heat-loving crops also being in the same area, but it is helpful when practical.
Growers should also review weather forecasts for the upcoming 24- to 48-hour periods before moving outdoors. A moderate temperature (no cooler than 40°F or warmer than 70°F), overcast day, with little or no wind is recommended.
A Few More Tips
For growers seeking expanded spring growing areas with minimal additional expense or risk, the option of finishing crops outdoors from early spring throughout the summer should be considered. Growers will find that not only can production be increased, but also overall quality. By balancing planting dates, growing crops both indoors and outdoors, and the flexibility of moving additional material outdoors or back into the greenhouse, a constant flow of high quality plant material should be available to the grower for supplying customers.