These cherry trees are growing in plastic bags so they can be put into cold storage in winter to delay bloom.

These cherry trees are growing in plastic bags so they can be put into cold storage in winter to delay bloom.

Each winter, Kevin Paulin moves a 1-1/2-acre block of his Sweetheart cherry orchard into cold storage.

Each of the 1,200 trees in the block is growing in a black plastic bag. In late July or early August, after the trees have gone dormant and been pruned, he loads them into bins, six trees in each, and hauls them to a cold storage facility that he rents, taking care not to knock off buds or twigs.

Why go to all that trouble? To give them a little extra winter and delay bloom so that he can have cherries on the market as late as possible, says Paulin, admitting that "it’s not for the faint hearted."

Chinese New Year

The trees are held in cold storage, at between 0° and 5°C (32° and 41°F), for about three months to manipulate the bloom timing. He can delay bloom by four to five weeks, which delays harvest by about three weeks. His aim is to export cherries to Taiwan for the Chinese New Year, and reap high returns.

He brings them out of storage in New Zealand’s spring, at the end of October, and sets them back in the orchard in rows. Fruit set is not usually a problem, he said, because the weather is better for pollination in November than in October.

Paulin has 50 acres of standard cherries, as well as nectarines and apricots, at his orchard in the Central Otago region of New Zealand. He thinks the bagged block produces larger cherries.

The bagged trees are on Colt rootstocks and are growing in crushed bark. All their nutritional requirements must be applied on a daily basis, since the trees have no reserves. They are "fed" every 25 minutes from 7 a.m. to 9 p.m. through an automated fertigation system. The "brew" is changed four or five times during the growing season. Calcium sprays are applied to the block once a week. He does leaf and fruit analysis about six times a year.

"They respond to what you give them very quickly," Paulin noted. "You’re giving them exactly what you want."

The block is protected by a rain cover and bird netting. The trees, now in their fifth leaf, produced between 5 and 6 kilos of fruit per tree, or 8 to 9 tons per hectare (about 3.5 tons per acre). Paulin thinks they will ultimately produce 15 to 16 tons per hectare (about 6 tons per acre).

This season, Sweetheart cherries from his regular cherry blocks were harvested on January 20, and fruit from the bagged trees three to four weeks later. He planned to store them for two to three weeks and have cherries for sale in March.

He figured they’d fetch at least N.Z.$20 per kilo (U.S.$6.35 per pound). "With the extra work, that’s what we need," he said.