Genesis 2:5

Because it had not rained (heading). And what was the reason it had not rained, because man did not yet exist to work the land and could not recognize the goodness of rain, and when man came and knew that they were needed for the world, he prayed about them and they fell, and the trees and the grass sprouted.

And all the trees of the field were not as yet in the earth, and all the herbs of the field had not as yet germinated, because the Lord God had not made it to rain upon the earth, and man was not to cultivate the ground.

AND EVERY SHRUB OF THE FIELD. In the opinion of our Rabbis in Bereshith Rabbah, [every herb of the field created] on the third day [did not come forth above the ground but] they remained just below the surface of the earth, and on the sixth day they grew after He caused rain to fall on them.
In my opinion, in accordance with the plain meaning of Scripture, on the third day the earth did bring forth the grass and the fruit trees in their full-grown stature and quality as He commanded concerning them. And now Scripture tells that there was no one to plant and sow them for future purposes, and the earth would not produce until a mist would come up from it and water it, and man was formed who would work it — to seed, to plant, and to guard. This is the meaning of the shrub of the field… had not yet grown. It does not say “the shrub of the ground” for only a place which is cultivated is called “field,” as in Which thou hast sown in the field and We will not pass through field or through vineyard. This is the course of the world that was to be following the six days of creation and forever after, that due to the mist the heavens will bring down rain, and due to the rains the earth will make the seeds that are sown in it to spring up.

טרם יהיה בארץ, these words emphasise that although all phenomena had been created, this referred to their potential, not to their functioning as they do nowadays. כל עשב השדה, had not yet sprouted,

כי לא המטיר, for G’d had not yet made it rain in such a fashion that it enabled the latent power of these plants to fully develop.

וכל שיח השדה, now the Torah fills in details of the report of G’d’s creative activity during the preceding days which had been omitted, including how man had spent the hours remaining on the sixth “day” after his creation. It refers to some aspects of the plants created already on the third “day,” as well as to the animals which had been created on the sixth “day” which share the same habitat as man, i.e. they live on dry land.
Seeing that the Torah would shortly have to refer to the vegetation in Gan Eden, including references to the trees of knowledge and the tree of life which are part of the vegetation on earth, the Torah first describes the fact that the shrubs, etc., had not yet been able to grow to their full maturity due to an absence of rain on earth. The fact that even shrubs are significant plants, is demonstrated in Genesis 21,15 where Hagar is described as abandoning her son Ishmael under one such shrub. At this point the Torah informs us that although in response to G’d’s directive on the third “day” that earth produce herbs, etc., and that in response to this directive the earth did indeed produce not only herbs but fruit-bearing trees, G’d had not yet decreed that rain fall on earth, seeing that man the beneficiary of such rain, had not been created as yet. Rain, by itself, without man working the soil does not accomplish a great deal.
This raises the question how the vegetation described as coming into existence on the third “day” managed to do so? The Torah answers this by describing vapours which rose from the surface of the waters at that time, and through whose influence all these plants were enabled to develop temporarily. There are numerous plants, shrubs included, which do not depend on man’s labour for their continued existence. The only plants which do require man’s input first and foremost, are the plants which serve as his food. David already referred to this in Psalms 104,14 where he describes that bread is produced from the earth and that rain is required to ensure that this will materialise. If the Torah, at the beginning of this verse, mentions that G’d had not let it rain, prior to mentioning that the vapour had risen (by itself, without G’d’s input, apparently) and had irrigated the earth, this was to inform us that rain is produced as a result of the vapours rising, forming clouds, etc, but that all of this needs to be initiated by G’d’s goodwill in the first place.
The gaon Rav Saadyah, in his commentary on …