Feb 18, 2009
Early Tomatoes Come From Careful Nurturing

If you are shooting for the early tomato market, you’ll plant an early variety, maybe 63 days. There is very little you can do to get that tomato ripe in less than 63 days – that’s inherent in the genes – but you can do lots of things to set the tomato back to 77 days or more, and reduce yield at the same time.

“You can bring a 63-day tomato to market in 63 days, if temperatures are absolutely right,” says Stephen Reiners, a horticulturist at Cornell University in Geneva, N.Y.

And that assumes other things are right as well. The light must be right when young plants are growing in the greenhouse. Transplant shock must be minimized when they are set in the field. And in the field, low temperatures or high temperatures translate into shock, stress and longer time to harvest.

Reiners gave a provocative talk during the Great Lakes Fruit, Vegetable and Farm Market EXPO in Grand Rapids in December, telling growers how to shoot for good yields of early tomatoes without using high tunnels.

“Many commercial growers who are trying to get the first tomatoes in the area will often grow transplants in large, four-inch pots,” he said. “In work I conducted in New Jersey, larger transplants did not produce any earlier fruit. “

The key is in avoiding transplant shock, he said. When transplanted, the plant responds by stopping all growth for a few days to a couple of weeks while gradually getting used to the new environment. But the key to avoiding transplant shock is not size but hardening. The plants must be gradually exposed to outdoor conditions and water and fertilizer cut back.

“The key is to get the plants growing again as quickly as possible after you plant, and a

properly hardened transplant will do just that.,” he said. “Should you go with larger sized plants? As long as they’re properly hardened, the larger plants would recover more quickly from transplant shock and will probably yield a little earlier.”

That is to say, you won’t lose as much time from your 63-day best shot.

While plants are growing from seed, light must be correct. Too little light causes plants to stretch and become spindly and to go into a reproductive phase, long before they have the size required for good yield.

Taking plants to the field with fruit already on them is not a good way to get early tomatoes; it’s a good way to get a lower yield because the plants will not grow to full size, he said.

“Tomatoes are warm season plants that cannot tolerate a frost,” Reiners said. “Even temperatures under 45˚ F will slow growth considerably.”

Two ways to assure temperatures don’t fall into that danger zone are to make sure the soil itself is warm and then to cover plants with row covers to protect them from losing heat at night.

“A plastic mulch that warms the soil will increase earliness as compared to bare ground planting,” he said. “There are basically three types of mulches you can use. “

Growers don’t choose clear plastic, he said, because weeds also love to germinate under plastic, and the temperature under clear plastic may be too hot and you could actually set the plants back with heat stress.

“Although tomatoes love heat, they do have their limits,” he said. “Nighttime temperatures that stay above 80 ˚ F will kill some of the pollen and prevent fruit set. Daytime temperatures above 90˚ may also have a similar effect.”

Black plastic suppresses weeds but doesn’t warm the soil as well as clear plastic. A third choice is thermal, or IRT, plastic mulches, which are colored and cost more. “I am not convinced they are worth the extra cost,” he said.

Organic mulches, like straw or a killed cover crop, work well for late season production, but actually slow down tomato growth early in the season by keeping soil cool.

Reiners recommends row covers as a way to get tomatoes out into the ground early and protect them from low temperatures. Row covers over plants grown in black plastic is a good combination – managed right.

“The protected conditions under row covers have resulted in early yield increases for muskmelons and other cucurbits but have had a mixed effect on peppers and tomatoes,” he said. “I found enhanced early yields of tomatoes using two type of row covers – floating, spunbonded covers and slitted, clear plastic.

“Other researchers have found the opposite – that yield was decreased with covers – and blamed that on temperatures that were too high under the cover. Apparently the yield loss in tomatoes grown under plastic may be related to insufficient pollination, blossom drop or fruit abortion.”

Row covers would seem to be most effective in allowing growers to plant several weeks earlier than traditional planting dates, Reiners said. The challenge when trying to plant tomatoes several weeks early is the inability to work the soil, prepare beds and lay plastic when the soil is still wet from spring rains.

“This is especially true on heavier soils that drain slowly,” he said. “In our row cover trials we could never plant as early as we hoped due to wet soils that could not be worked.”

To overcome that problem, he tried preparing beds the previous fall, in October, laying the trickle irrigation lines and the black plastic. The next spring, tomatoes were planted on April 13 – “five weeks before most growers would traditionally plant,” he said. Then they were covered with clear, slitted plastic row covers.

There were no freezes that spring, he said, but the temperature fell below 40 ˚ on nine of the first 18 nights, he said.

The result was more early tomatoes.

Since there were no freezes to kill the tomato plants, those planted April 13 with no protection did produce 2,400 pounds of tomatoes. Those planted April 13 and covered until May 20 – the normal no-more-freezes date – yielded 7,500 pounds. Leaving the covers on until June 10 gave 8,300 pounds of tomatoes.

Reiners concludes that growers can get early tomatoes by planting early, even without protection, but needing some luck.

Under the covers in the experiment, on three days out of the first 50 temperatures under the covers covers did exceed 95˚ F, and one day it exceeded 100 ˚ F.

“There was no advantage to leaving covers on past the time when tomatoes were traditionally planted.,” he said. “In fact, the date of traditional planting may serve as an effective guideline to indicate when to remove the row covers to avoid the possibility of problems from heat.

“These experiments clearly demonstrate that row covers, if used at the proper time, can increase the early yield of tomatoes. Their effectiveness, however, seems to be related to allowing earlier planting rather than accelerating the ripening of later planted tomatoes.

The higher temperatures under row covers may decrease the yield in plantings made at traditional times, so row covers offer no advantage on those tomatoes.

“Fall bedding seems to be a viable option for growers interested in maximizing the ability to plant very early in the spring,” he said.

Growers can make double use of row covers, using them to extend the season into the fall.

Tomatoes lose their flavor quickly when temperatures fall below 55 ˚ F, he said.

Mature, but still green, tomatoes (those with hardened seeds) will ripen if picked and placed in a warm, well-ventilated, dark place – and that may provide a better alternative than row covers as the season ends.




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