Summer lay warm upon the hills and river; the landscape was yet untouched by the scorching July heats; and on the seventh of June, 1838, — he being then in his twenty-third year, — Downing was married to Caroline, eldest daughter of J. P. De Wint, Esq. At this time, he dissolved the business connection with his elder brother, and continued the nursery by himself. There were other changes also. The busy mother of his childhood was busy no longer. She had now been for several years an invalid, unable even to walk in the garden. She continued to live in the little red cottage which Downing afterwards removed to make way for a green-house. Her sons were men now, and her daughter a woman. The necessity for her own exertion was passed, and her hold upon life was gradually loosened, until she died in 1839.
Downing now considered himself ready to begin the career for which he had so long been preparing; and very properly his first work was his own house, built in the garden of his father, and only a few rods from the cottage in which he was born. It was a simple house, in an Elizabethan style, by which he designed to prove that a beautiful, and durable, and convenient mansion, could be built as cheaply as a poor and tasteless temple, which seemed to be, at that time, the highest American conception of a line residence. In this design he entirely succeeded. His house, which did not, however, satisfy his maturer eye, was externally very simple, but extremely elegant; indeed, its chief impression was that of elegance. Internally it was spacious and convenient, very gracefully proportioned and finished, and marked every where by the same spirit. Wherever the eye fell, it detected that a wiser eye had been before it. All the forms and colors, the style of the furniture, the frames of the mirrors and pictures, the patterns of the carpets, were harmonious, and it was a harmony as easily achieved by taste as discord by vulgarity. There was no painful conformity, no rigid monotony, there was nothing finical nor foppish in this elegance — it was the necessary result of knowledge and skill. While the house was building, he lived with his wife at her father's. He personally superintended the work, which went briskly forward. From the foot of the Fishkill hills beyond the river, other eyes superintended it, also, scanning, with a telescope, the Newburgh garden and growing house; and, possibly, from some rude telegraph, as a white cloth upon a tree, or a blot of black paint upon a smooth board, Hero knew whether at evening to expect her Leander.
The house was at length finished. A graceful and beautiful building stood in the garden, higher and handsomer than the little red cottage — a very pregnant symbol to any poet who should chance that way and hear the history of the architect.
Once fairly established in his house, it became the seat of the most gracious hospitality, and was a beautiful illustration of that "rural home" upon whose influence Downing counted so largely for the education and intelligent patriotism of his countrymen. His personal exertions were unremitting. He had been for some time projecting a work upon his favorite art of Landscape Gardening, and presently began to throw it into form. His time for literary labor was necessarily limited by his superintendence of the nursery. But the book was at length completed, and in the year 1841, the Author being then twenty-six years old, Messrs. Wiley & Putnam published in New York and London, "A Treatise on the Theory and Practice of Landscape Gardening adapted to North America, with a view to the Improvement of Country Residences. With Remarks on Rural Architecture. By A. J. Downing." The most concise and comprehensive definition of Landscape Gardening that occurs in his works, is to be found in the essay, "Hints on Landscape Gardening." " It is an art," he says, "which selects from natural materials that abound in any country its best sylvan features, and by giving them a better opportunity than they could otherwise obtain, brings about a higher beauty of development and more perfect expression than nature herself offers." The preface of the book is quite without pretence. "The love of country," says our author, with a gravity that overtops his years, "is inseparably connected with the love of home. Whatever, therefore, leads man to assemble the comforts and elegancies of life around his habitation, tends to increase local attachments, and render domestic life more delightful; thus, not only augmenting his own enjoyment, but strengthening his patriotism, and making him a better citizen. And there is no employment or recreation which affords the mind greater or more permanent satisfaction than that of cultivating the earth and adorning our own property. 'God Almighty first planted a garden; and, indeed, it is the parent of human pleasures,' says Lord Bacon. And as the first man was shut out from the garden, in the cultivation of which no alloy was mixed with his happiness, the desire to return to it seems to be implanted by nature, more or less strongly, in every heart".
This book passed to instant popularity, and became a classic, invaluable to the thousands in every part of the country who were waiting for the master-word which should tell them what to do to make their homes as beautiful as they wished. Its fine scholarship in the literature and history of rural art; its singular dexterity in stating the great principles of taste, and their application to actual circumstances, with a clearness that satisfied the dullest mind; its genial grace of style, illuminated by the sense of that beauty which it was its aim to indicate, and with a cheerfulness which is one of the marked characteristics of Downing as an author; the easy mastery of the subject, and its intrinsic interest; — all these combined to secure to the book the position it has always occupied. The testimony of the men most competent to speak with authority in the matter was grateful, because deserved, praise. Loudon, the editor of "Repton's Landscape Gardening," and perhaps at the time the greatest living critic in the department of rural art, at once declared it "a masterly work;" and after quoting freely from its pages, remarked: "We have quoted largely from this work, because in so doing we think we shall give a just idea of the great merit of the author." Dr. Lindley, also, in his " Gardener's Chronicle," dissented from "some minor points," but said: " On the whole, we know of no work in which the fundamental principles of this profession are so well or so concisely expressed:" adding, "No English landscape gardener has written so clearly, or with so much real intensity".