“If you stress these plants, you shut them down. They’ll sit there for a few days while they recover and then you’ve lost some of the advantage”
An extra few days on either side of our short season can make a big difference to a commercial vegetable grower. Rob Spencer, commercial horticultural specialist with Alberta Agriculture in Stettler, recently outlined some strategies at the Berry and Vegetable School, hosted by the Alberta Farm Fresh Producers Association.
Climatic zones and growing seasons vary widely across the province. The growing season, which changes every year, is generally delineated by the last spring frost and the first fall frost. That leaves two options – starting earlier or harvesting later.
An extended growing season can help a commercial producer beat others to market, or it can extend the harvest and supply consumers for a longer period. “We’re talking about bringing in extra money through different techniques,” said Spencer.
One strategy is to accept that growing seasons are short and select crops accordingly. Trying to grow outside the estimated spring and fall frost dates can allow a few extra growing days, but increases risk.
Site selection is another strategy. Spencer advised producers to pick an advantageous location. For example, sandier soil warms up faster, which can be beneficial for some crops. Others will do better in sheltered locations.
Fall seeding is yet another option. Spencer said this strategy is not guaranteed, but may work well with some crops such as garlic. This approach capitalizes on some of the moisture available in the early spring.
Using transplants is another way producers can grow plants well before the growing dates. Plants can be started indoors in a cold frame or greenhouse, and moved outside when conditions are suitable.
“You can gain days or weeks of growing time if you handle this right. I’m a big fan of transplants, but it doesn’t necessarily work for every crop,” he said.
Transplants allow for a better stand, good root development and have the potential for earlier and higher yields because using transplants allows the producer to have a better grasp of his or her plant population. Spencer recommended choosing transplants with good, unbound root systems. Plants should be strong and healthy, hardened off to a certain extent, free from disease and insects, a good age and not stressed or overly succulent.
Producers should take care not to move transplants directly from a warm greenhouse out into a cold or frozen soil. It’s best to transplant during a cooler or overcast part of the day, to reduce the stress on the plants.
“If you stress these plants, you shut them down. They’ll sit there for a few days while they recover and then you’ve lost some of the advantage,” said Spencer.
Creating an environment conducive to growth, known as microclimate management, is another way producers can create a few more days of growth. Microclimate management can include mulching, row covers, field covers, high tunnels and greenhouses.
Mulch, which encompasses plastic or organic varieties such as straw or wood chips, increases or decreases the soil temperature and increases moisture content. Mulch generally inhibits weed growth, except when clear mulch is used. Disposal of mulch is often a major issue, and the application of the plastic mulches may require specialized equipment. Using mulch can also result in additional costs.
Clear plastic mulch will raise soil temperature significantly, but can also increase weed growth. Black mulch has excellent weed control, but does not significantly increase soil heat. Other mulches include a wavelength-selective mulch, biodegradable mulches and organic mulches. Wavelength-selective mulch provides the benefits of heat trapping of the clear mulch, with weed control benefits of the black mulch. Organic mulches do not extend seasonal growth, but can be used to create heat during the season and help retain moisture.
Row covers can include low or mini tunnels placed over rows of plants, usually supported with hoops. These structures can enhance early or in-season growth and are covered with plastic, perforated plastic or Reemay. Row covers have to be removed once a certain level of growth has taken place, or when the plants inside start to flower. Perforated plastic allows heat to escape from the structure, and these covers can generally be left on for a while longer. “You do get some crop protection if there’s an early frost,” said Spencer.
Other structures which may accelerate growth include field covers, which float over the crops and are anchored, cold frames and greenhouses.