For America's horticulturists, it's the sort of problem that could make a person pack up his petunias and go home.

Their "specially designed, single-purpose, environmental growth chambers" don't qualify for investments tax credits.

The rest of America calls these chambers greenhouses, and yesterday they were the focus - briefly - of a House subcommittee.

The Internal Revenue Service says growth chamber or no growth chamber, greenhouses are just buildings, and buildings don't get the investment tax credit.

The horticulturists and florists disagree, and, since it makes a $5 million difference, they've taken their fight to Congress.

That's why Timothy Burns and Jeff McDonald appeared yesterday before the subcommittee on miscellaneous revenue measures of the House Ways and Means Committee, a group that has a heavy hand in writing the nation's tax laws.

The florists were accompanied by representatives of the Puerto Rican savings and loans, ship chandlers and a water authority, each seeking a "technical revision" in the tax code that is small compared to the entire budget but means big money for the people involved.

Burns, director of governmental affairs for the Society of American Florists and Ornamental Horticulturists, kept his remarks brief. He spoke at length on the issue a week ago, when the subcommittee considered the similar plight of henhouse owners, so the committee members were familiar with the florists' views.

Burns took time, however, to counter the statement by a Treasury Department representative that the committee shouldn't act piecemeal, but wait to consider President Carter's proposal on expanding the investment credits to all industrial structures.

The president's proposal might not even cover greenhouses, Burns said, because they aren't just industrial structures. They are, yes, "specially designed, single-purpose, environmental growth chambers."

The investment tax credit, which lets companies apply 10 per cent of the cost of their investment against their tax bill, would be an important break for greenhouse operators. Burns said the benefits, ranging from several hundred dollars for most operators to several thousand dollars for big companies, would help finance expansion.

The florists are a little bewildered by why they even have to tight this battle. They say greenhouses are just as much a piece of machinery or "special purpose structure" as the electrical generators and farmers' fences that already qualify for the credits.

"Greenhouses are a piece of machinery in the growing of flowers and plants. It's as simple as that," Burns said. "Without a greenhouse, you can't do it. Besides, what else are you going to use a greenhouse for'?"

The 9th U.S. Circuit Court of Appeals has agreed with the florists, but the Internal Revenue Service hasn't. So it is still thumbs down when the florists file for the credit.

Now it's back to Congress, to settle what Burns calls "a gut issue, an issue for the very survival of the industry."

The horticulturists won't give up their "specially designed, single-purpose, environmental growth chambers" without a fight.