It turns out that the correct spelling is "Brant-Hentz." Misspelling "Brandt-Hentz" appears to have originated in the pages of the ARS Annual of 1922, p. 168. The company itself was no longer in business by that time: "The Noe & Ruzicka Co. Inc. Incorporators, L. A. Noe, Jos. F. Ruzicka. Capital $ 75,000 . The above firm purchased the plant of the Brant-Hentz Floral Co. and after some changes will continue to grow roses. Mr. Brant is leaving Madison to devote his time to the extensive plant of Brant Bros. at Utica, N.Y." (from periodical Horticulture, vol. 24, 1916, p. 686).

Originally Brant and Hentz were neighbors. Here's some background from 1903, filling in some data relevant to the above quote from 1916: "One of the oldtime places still produces roses of the first class. This is the old Slaughter place, now leased by Elwood Brant. There are some seventeen houses here,accommodeating about 30,000 plants. [American] Beauties are the chief crop grown, with teas along the front benches. Two houses of Liberty and one of Meteor are also grown. The houses are antiquated compared with the modern standard, but the stock looks very good indeed and reflects great credit on Mr. Brant. He is a shrewd young man who is forging ahead and is part lessee with his brother of the immense rose houses of Peter Crowe, of Utica, N.Y. Most of the largest growers here [Madison, N.J.] live, as Mr. Dooley would say, 'beyont the thracks,' or above the railroad. Just a stone's throw from Mr. Brant is the handsome range of Henry Hentz, Jr. It is a modern plant, complete in every particular, and is of the most enduring construction. Beauties are chiefly grown. [...] Mr. Hentz is a partner of the firm of Moore, Hentz & Nash, which is the donor of the special medals offered at the show every year by the local horticultural society. [...] Not far from the last named establishments are the plants of Louis M. and Louis A. Noe, father and son respectively, the Beauty kings of Madison. Each has some nineteen or twenty houses 200 feet long and the stock can only be described as splendid." From Florists' Review, vol. 12, 1903, pp. 752-753.