Emil Schürer writes (The Literature of the Jewish People in the Time of Jesus, pp. 329-331):

While this shorter explanation in a catechetical form [Questions and Answers on Genesis] was intended for more extensive circles, Philo’s special and chief scientific work is his large allegorical commentary on Genesis, Νομων ιερων αλληγοριαι (such is the title given it in Euseb. Hist. eccl. ii. 18. 1, and Photius, Bibliotheca cod. 103. Comp. also Origen, Comment. in Matth. vol. xvii. c. 17; contra Celsum, iv. 51). These two works frequently approximate each other as to their contents. For in the Quaestiones et solutiones also, the deeper allegorical significance is given as well as the literal meaning. In the great allegorical commentary on the contrary, the allegorical interpretation exclusively prevails. The deeper allegorical sense of the sacred letter is settled in extensive and prolix discussion, which by reason of the copious adducting of parallel passages often seems to wander from the text. Thus the entire exegetic method, with its draggin in of the most heterogeneous passages in elucidation of the idea supposed to exist in the text, forcibly recalls the method of Rabbinical Midrash. This allegorical interpretation however has with all its arbitrariness, its rules and laws, the allegorical meaning as once settled for certain persons, objects and events being afterwards adhered to with tolerable consistency. Especially is it a fundamental thought, from which the exposition is everywhere deduced, that the history of mankind as related in Genesis is in reality nothing else than a system of psychology and ethic. The different individuals, who here make their appearance, denote the different states of soul (τροποι της ψυχης) which occur among men. To analyse these in their variety and their relations both to each other and to the Deity and the world of sense, and thence to deduce moral doctrines, is the special aim of this great allegorical commentary. Thus we perceive at the same time, that Philo’s chief interest is not—as might from the whole plan of his system be supposed—speculative theology for its own sake, but on the contrary psychology and ethic. To judge from his ultimate purpose he is not a speculative theologian, but a psychologist and moralist (comp. note 183).

The commentary at first follows the text of Genesis verse by verse. Afterwards single sections are selected, and some of them so fully treated, as to grow into regular monographs. Thus e.g. Philo takes occasion from the history of Noah to write two books on drunkenness (περι μεθης), which he does with such thoroughness, that a collection of the opinions of other philosophers on this subject filled the first of these lost books (Mangey, i. 357).

The work, as we have it, begins at Gen. ii. 1; Και ετελεσθησαν οι ουρανοι και η γη. The creation of the world is therefore not treated of. For the composition, De opificio mundi, which precedes it in our editions, is a work of an entirely different character, being no allegorical commentary on the history of the creation, but a statement of that history itself. Nor does the first book of the Legum allegoriae by any means join on to the work De opificio mundi; for the former begins at Gen. ii. 1, while in De opif. mundi, the creation of man also, according to Gen. ii, is already dealt with. Hence—as Gfrörer rightly asserts in answer to Dähne—the allegorical commentary cannot be combined with De opif. mundi as though the two were but parts of the same work. At most may the question be raised, whether Philo did not also write an allegorical commentary on Gen. i. This is however improbable. For the allegorical commentary proposes to treat of the history of mankind, and this does not begin till Gen. ii. 1. Nor need the abrupt commencement of Leg. alleg. i seem strange, since this manner of starting at once with the text to be expounded, quite corresponds with the method of Rabbinical Midrash. The later books too of Philo’s own commentary begin in fact in the same abrupt manner. In our manuscripts and editions only the first books bear the title belonging to the whole work, Νομων ιερων αλληγοριαι. All the later books have special titles, a circumstance which gives the appearance of their being independent works. In truth however all that is contained in Mangey’s first vol.—viz. the works which here follow—belongs to the book in question (with the sole exception of De opificio mundi).

Emil Schürer comments:
“Περι γεωργιας. De agricultura (Mangey, i. 300-328). On Gen. ix. 20a.—Περι φυτουργιας Νωε το δευτερον. De plantatione Noe (Mangey, i. 329-356). On Gen. ix. 20b. The common title of these two books is properly περι γεωργιας. Comp. Euseb. H. E. ii. 18. 2: περι γεωργιας δυο. Hieronymus, De vir. illustr. 11: de agricultura duo. Euseb. Praep. Evang. vii. 13. 3 (ed. Gaisford): εν τω περι γεωργιας προτερω. Ibid. vii. 13. 4: εν τω δευτερω.” (The Literature of the Jewish People in the Time of Jesus, p. 335)

J. H. A. Hart writes (The Jewish Quarterly Review Original Series 17, pp. 103-107):
The tract On Husbandry deals with the section (Gen. ix. 20 f.) which introduces the righteous Noah as a husbandman. The very title shows how Moses always uses the right word, for γεωργια differs from γης εργασια as implying skill and care for the ground worked. And from the consideration of the culture of the ground we are naturally led on to consider the culture of the soul. Just as all cultivated plants and trees bear yearly fruit for the service of man, so in the soul will the mind, which is the man in each one of us, reap fruit of the nurture supplied—general education, corresponding to the child’s milk or advanced instruction corresponding to the bread of the man. All trees of folly and wickedness must be torn up, roots and all. Such as bear fruit, neither profitable nor harmful, must be used as bulwarks (Deut. xx. 20). For philosophy has been compared to a field by the ancients; physical philosophy stands for the plants and trees, ethical for their fruits for whose sake they exist, and logical for the fence which guards them. So the plants sown by the agriculturist of the soul are first the practice of reading and writing readily, the exact investigation of the teaching of wise poets, geometry, rhetoric—in fact, all general education; and then the better and more perfect studies, the tree of understanding, of courage, of soberness, of righteousness, and of every virtue. Accordingly Moses ascribes to the righteous Noah the art of agriculture, and to Cain the working of the ground, unskilled and burdensome.

These two terms then appear synonymous, but once we allegorize according to the mind of Scripture we find they are very different. So also is it with the terms “shepherd” (ποιμην) and “tender of flocks” (κτηνοτροφος). Both are applied to the reason, but the first to the good, the second to the bad. The soul of each one of us puts forth two shoots, which are the flocks of our nature: the one undivided, whole throughout, is called mind; the other splits into seven natures, the five senses and the powers of speaking and generation. If then a man declare himself his own master, he brings a multitude of evils upon these nurslings of his. Those then who provide them with all the nourishment they ask must be called tenders of flocks; and those who give them enough and no more, circumcising and cutting off excessive and useless profusion, are shepherds. Hence the honour paid to the art of shepherds, practised by Moses for example, in the poets and in Scripture. The Lord’s congregation shall not be like sheep which have no shepherd (Num. xxvii. 17). For lack of a shepherd leads to mob-rule (Ochlocracy), that counterfeit of goodly Democracy, just as does the sway of a tyrannical or of an over-lenient governor. And the shepherd is God, who puts forth his right Reason and first-born Son to take over the care of this holy flock, the universe, like a satrap of the great king (Exod. xxiii. 20). Let the whole world then, no less than the individual, say, “The Lord is my shepherd” (Ps. xxii. 1). Such disciples of God laugh at the tending of flocks, and have worked out the skill of shepherds, as may be seen in the story of Joseph and his brethren. Joseph—he that is ever occupied with the body and vain opinions—the ever-youthful, bids the lovers of virtue avow themselves tenders of flocks to Pharaoh, the king of the land of passions (Gen. xlvi. 33 f.); but they, true to themselves and their fathers, say: “We are shepherds, come to sojourn, not to settle” (Gen. xlvii. 3 f.). For in truth every wise man’s soul holds heaven for fatherland, earth for a strange country.

Here again the allegorical method has led Philo to reverse the ordinary estimate of Joseph and his brethren. But the new view only holds good when applied to detached incidents, and in the tract de Josepho, which deals with the whole story, Joseph comes by his own again.

Another pair of so-called synonyms is “horseman” and “rider.” The horseman is skilled in guiding and controlling his steed, while the rider is unable even to hold the reins and is thrown after a wild and random career. “Horses,” of course, stand for lust and anger (e. g. in the προτρεπτικα of Moses, Deut. xx. 1), against which God, by his army of the virtues, defends the souls that love him. And after the victory the song of thanksgiving is sung (Exod. xv, especially verses 1, 20). No horseman, Moses says in the admonitions (ταις παραινεσεσιν), is to rule over Israel (Deut. xvii. 15f.). It is not unnatural therefore that he should pray for the complete destruction of the horsemen (Exod. xv), and the prayer is given in Gen. xlix. 17f., which needs explanation. Dan, “judgment,” is the faculty of the soul which examines, investigates, discerns, and, in a way, judges each action, and is therefore likened to the serpent, not the friend and counsellor of Life (which is called Eve in the language of the Fathers), but the Brazen Serpent. The two stories referred to may appear mythical, but in the allegorical explanations (εν ταις δι υπονοιων αποδοσεσι) the mythical element is entirely removed, and the truth found plain. Eve’s serpent is pleasure, unable to rise, which bites man’s heel. Moses’ is endurance, the opposite of pleasure, which bites the horse’s heel. The prophecy that “the horseman shall fall” leads to the reflexion that he who is mounted on and carried away by any passion is happiest in falling, that he may rise to virtue. Such defeat is better than victory. And so Philo comes to consider the sacred games of Greece. Surely they are not really sacred if the prize be awarded for pitiless brutality, which the laws condemn. So then that Olympic contest alone may lawfully be styled sacred—not that which the men of Elis hold—but the contest for possession of the divine and truly Olympian virtues, for which they who are weakest in body but strongest in soul are all entered.

So much then for these pairs of words. It is time to turn to the rest of the text. “Noah began to be an husbandman.” The beginning, according to the ancient proverb, is half of the whole, but, if the rest be wanting, it is harmful. So it was in the case of Cain (Gen. iv. 7). His honour of God is right, but not his lack of discernment. And there are some like him who make piety consist in the assertion that all things are made by God, whether they be good or not. It is absurd that priests and offerings should be examined for blemishes before coming to the altar, and yet the opinions about God in each man’s soul be left in confusion. Seest thou not that the camel is an unclean beast, because it chews the cud, but does not divide the hoof (Lev. xi. 4)? The reason alleged has nothing to do with the literal interpretation, everything to do with the allegorical interpretation. Rumination stands for memory, and memory must discriminate. Both memory and discrimination are necessary to any real progress.

Daily the herd of sophists tickles the ears of their hearers with endless discriminations and divisions, and grammarians, musicians and philosophers follow suit. Yet neither they nor their hearers are bettered. Rightly are such compared to swine, unclean because they divide the hoof, but do not chew the cud (Lev. xi. 7). But from their wordy warfare all who have made a beginning or progress, or attained perfection, are exempt, for the Law thinks it right that a man should be trained not merely in the acquisition of good things, but also in the enjoyment of what he has acquired (Deut. xx. 5-7). Descend not then into the arena lest another receive the virtues typified by house, vineyard, wife. Enter then the new house—culture that never grows old—crown not thyself rather than God; slay not thus thy soul, but remember God that giveth thee strength to do power (Deut. xxii. 8; viii. 18).

So much of Noah, who gained the first elements of the art of husbandry and then fell weak. What is said of his vine-dressing let us speak on another occasion.

F. H. Colson and G. H. Whitaker write (Philo, vol. 3, pp. 104-107):

Gen. ix. 20 f. quoted at the beginning of De Agricultura is the text of this and the two following treatises. The part of it dealt with in the one before us is the words, “And Noah began to be a husbandman” or “gardener.”

Having pointed out that this connotes scientific gardening, Philo describes scientific gardening in the literal sense (1-7), and then goes on to soul-gardening. This ministers to the Mind. Its aim is the fruit of virtue, and it is only for the sake of this that it occupies itself first with rudimentary subjects. What is harmful it prunes away. What is not fruit-bearing it uses for fencing. It deals in this way with mere theorizing, forensic speech, dialectics, and geometry, which all sharpen the intellect without improving the character (8-16). Soul-gardening sets out its programme (17 ff.). As such a soul-gardener righteous Noah is contrasted with Cain, who is a mere “worker of the earth” in the service of Pleasure (21-25).

There must surely be other pairs of opposites similar to this of the scientific tiller and the mere worker of the soil. Yes; there is the shepherd and the rearer of cattle. The organs of the body are the cattle of each one of us. A careless Mind is unfit to guard them; it will not check excess, or exercise needful discipline. These things a shepherd will do. So honourable is his calling that poets call kings “shepherds,” and Moses gives this title to the wise, the real kings. Jacob was a shepherd. So was Moses; and he prays God not to leave Israel un-shepherded, i.e. to save it from mob-rule, despotism and licence. Well may each of us make his prayer our own on behalf of our inner flock. God, the Shepherd and King of the Universe, with His Word and Firstborn Son as viceroy, is extolled in the Psalm “The Lord shepherds me.” Only by the One Shepherd can the flock be kept together. This is our sure hope, and our sole need. So all who were taught by God made the shepherd’s science their study, and their pride; like Joseph’s brethren who, though bidden by him to tell Pharaoh that they were “rearers of cattle,” answered that they were “shepherds,” shepherding, i.e. the faculties of the soul; for Pharaoh, with royal and Egyptian arrogance, would have looked down on keepers of literal goats and sheep. The fatherland of these soul-shepherds is Heaven, and (as they told the King) they were but “sojourners” in Egypt, the land of the body and the passions (26-66).

We find in the Law a third pair of opposites. A sharp distinction is to be drawn between a “horseman” and a “rider.” The mere “rider” is at the horse’s mercy; the horseman is in control like the man at the helm. The horses of the soul are high spirit and desire, and their rider the Mind that hates virtue and loves the passions. Israel’s “Song by the Sea” celebrates the disaster that befalls the “four-footed throng of passions and vices.” It is clear that Moses’ words about horses are symbolic, for so great a soldier as he must have known the value of cavalry. Again, though literal racehorse breeding is a poor business, those who ply it have the excuse that the spectators of a race catch the fine spirit of the horses; whereas the figurative trainer, who sets ari unqualified jockey on the back of vice and passion, is without excuse (67-92).

A glance at the prayer of Moses in Gen. xlix. 17 f. will shew how different the “horseman” is from the “rider.” To understand that prayer we must note that “Dan” means “judgement,” and that the “dragon,” which he is or has, is Moses’ serpent of brass. (Of course neither Moses’ serpent nor Eve’s can be literal. Serpents do not talk, tempt, or heal.) So Moses prays that Dan (or his serpent) may be on the road ready to assail Pleasure, and “bite the horse’s heel,” i.e. attack and overturn the supports which hold up Passion (94-106).

Here we come upon a piece of interpretation very characteristic of Philo. The biting of Passion’s heel brings about the horseman’s fall. So far from being daunted by this, our author positively revels in it. It is a fall which implies victory, not defeat. For, should Mind ever find itself mounted on Passion, the only course is to jump or fall off. Yes, if you cannot escape from fighting in a bad cause, court defeat. Nay, do not stop there. Press forward to crown the victor. The crown at which you are aiming is not won in contests of pitiless savagery, or for fleetness of foot, in which puny animals surpass men, but in the holy contest, the only true “Olympic” games, the entrants for which, though weaker in body, are strongest in soul (108-119).

Having noted the difference between the members of each of these three pairs of opposites, suggested to him by the word γεωργος in his text, Philo turns to the word ηρξατο, “began” (124).

“Beginning is half the whole.” Yes, if we go on to the end. But good beginnings are often marred by failure to make proper distinctions. For instance, one says that “God is the Author of all things,” whereas he should say “of good things only.” Again, we are very scrupulous about rejecting priests or victims on the ground of physical blemish. We ought to be equally scrupulous to separate the profane from the sacred in our thoughts of God. And again Memory, of which the ruminating camel is a figure, is a fine thing, but the camel’s undivided hoof makes him unclean, and that reminds us that Memory must reject the bad and retain the good; for practical purposes, not for sophistical hair-splitting. Sophists are swine; they divide ad nauseam, but for perfection we must con over and take in (125-146).

Sections 147 to 156 shew that the conditions of exemption from military service laid down in Deut. xx. 5 and 7 cannot be literally meant. In 157 ff. the acquired possessions which exempt a man are interpreted as faculties which must be enjoyed and fully realized, before he who has acquired them is trained and fit for the warfare with the sophists.

Right ending must crown good beginning. We miss perfection unless we own that that to which we have attained is due to the loving wisdom of God. And wilful refusal to acknowledge God as the Giver of success is far worse than involuntary failure.

“All this about start and goal has been suggested,” Philo tells us, “by the statement that Noah began to be a husbandman or gardener.”