NATICK, Mass. (AP) — When a Navy submarine goes to sea on a monthslong voyage, the lettuce, tomatoes and other fresh fruits and vegetables on board run out in a week or two, forcing the crew to rely on canned, frozen or dehydrated products.

But what if subs had their own gardens where food could be grown under lights?

The U.S. military is testing out the idea by growing plants hydroponically – that is, with nutrient solution instead of soil – inside a 40- foot shipping container on dry land at a laboratory outside Boston.

Engineering technician Don Holman, who grew up on a farm in Michigan before serving 30 years in the Navy, is running the $100,000 project at the Army’s Natick Soldier Research, Development and Engineering Center. He said sailors have been asking for more produce.

“When you give someone something they want, it improves their morale. And they perform better when morale is up,” said Holman, who will present a technical report in September so the Navy can decide whether to attempt gardening beneath the sea.

This is the second phase of the testing. Holman first tried to grow 83 varieties of fruits and vegetables to see which ones did best. The leafy greens and green onions thrived. Root vegetables did fairly well. Strawberries and rhubarb grew but probably wouldn’t produce enough to make it worthwhile, Holman said.

The cucumbers, on the other hand, were a mess. The vines climbed everywhere. And the large leaves on the zucchini plants blocked the lights. The tomato plants grew but didn’t produce fruit because the lighting wasn’t bright enough and the temperature was too low.

Holman replanted the varieties that did well. He is now tending to those seedlings to see how much they produce.

On the dirt- and insectfree “farm,” as Holman calls it, the plants are growing in trays of peat moss plugs and will be transferred this week to more than 250 towers suspended from overhead tracks and filled with growing material made of recycled plastic. Strands of red and blue LED lights dangle from the ceiling.

He said vegetables could be planted before a vessel went to sea so that they would be ready for harvesting during the mission.

Retired Navy Capt. Ronald Steed, a former sub skipper, said it would be a real challenge to fit a garden on a submarine, where space is extremely tight, “but if they could do it, that would be awesome.”