According to the Hartlib Circle members’ interest for vegetable philosophy, I have been able to identify three different approaches associated with three different stages.
The first stage (the period until 1650) is dominated by the figure of Gabriel Plattes.  He is the first member of the Hartlib Circle expressing his vision upon vegetable philosophy and husbandry regarded as projects of ameliorating the material of Creation (soil, plants, human beings). Inspired from Bacon’s natural philosophy and sharing the general ideas animating the Circle, he considers amelioration a process of experimentation and technological improvement of the material of Creation. Plattes reformulates the view on husbandry, promoting a new type of ‘integrated science’ able to cultivate the land and the human soul as well. Apart from other tracts on husbandry published before, Plattes used the alchemical tradition but committed the application of chemistry to a moral end. He developed his own experimental view on vegetable philosophy, placing at the very core of amelioration the idea of technological advancement (a project based on transmutation experiments and cyclical chemical change). Plattes’ contribution rests in providing a number of ‘technologies of amelioration’ for the material of Creation (soil, plants, human beings), technologies of salvation compatible with both economic advancement and religious salvation.
The second stage (1650-1660) is influenced in a great deal by the figure of Gabriel Plattes. All the writers on vegetable philosophy and husbandry (Austen, Blith, Dymock, Child, Beale, Weston and, later, Evelyn) mention Plattes in their works and his contribution to the field. Writers of this stage express strong millenaristic beliefs due to their association with the Hartlib Circle and Samuel Hartlib. They continue the line imposed by Plattes, of technological experimentation and amelioration of the material of Creation but add grafting experiments. In this stage we can spot a shift of attention from alchemical transmutation to gardening, from experiments with minerals and metals to experiments with plants. The Virgilian influence is evident in this stage. We can include in this stage a part of Evelyn’s activity, the one chronologically associated with the Civil War. Due to his aristocratic affiliation, Evelyn experienced social isolation and he imagined different hortulan societies, living in perfect harmony with nature, sharing interest for the study of nature and for exploring the practical and spiritual possibilities of vegetable philosophy.
The third stage (the period after 1660), associated with the beginning of the Royal Society is characterized by amelioration accents only in a small deal. If Evelyn’s Elysium Britanicum (started in the late 1650s) begins with his personal interpretations of the Genesis, the accent embedded in his 1660 works (such as Sylva and Pomona) is more scientific than religious. Austen, for instance, republished his treatise of Fruit-Trees and rededicated it to Royal Society Fellow Robert Boyle (see Austen Treatise, 3rd edition Oxford, 1665; Treatise of Fruit Trees, with the Spiritual Use of and Orchard (1653 – first edition). The first edition had been dedicated to Samuel Hartlib. The Royal Society revealed the so called closely guarded secrets and the spiritual reformed, so much embraced by Hartlib, was downplayed. 
 Plattes, G., A Discovery of Infinite Treasure, London, 1639.
Plattes, G., A Discovery of Subterraneall Treasure, London, 1639.
 Such as Sir Hugh Plat’s Jewell House of Art and Nature, London, 1594. Although he had a deep interest in chemistry, medical chemistry and ways to improve the barren soil, Sir Hugh Plat was more influenced by the alchemical tradition (Paracelsus, John Hester, Bernard Palissy) than the desire to ameliorate the human estate.
 Here is a short list including treaties on husbandry and vegetable philosophy issued in the 1650s inside the Hartlib Circle :
Dymock, C., An Invention of Engines of Motion Lately Brought to perfection. … London, 1651;
[Hartlib], S., Dymock, C., An Essay for the Advancement of Husbandry –Learning: or Propositions For the Erecting a College of Husbandry … London, Printed by Henry Hills, 1651.
Hartlib, S., Samuel Hartlib his Legacy: or an Enlargement of the Discourse of Husbandry used in Brabant and Flandres … London, 1651.
Child, R., A Large Letter concerning the Defects and Remedies of English Husbandry written to Samuel Hartlib by Sir Richard Child (part of Samuel Hartlib his Legacy).
Blith, W., The English Improver Improved, The Third Impression, London, 1652.
[Virginia Ferrar, et al.], A Rare and New Discoverie of a Speedy Way, and Easie Means … for the Feeding of Silk-Worms, London, 1652.
Boate, G., Irelands Naturall History. Being a true and ample Description of its Situation, Greatnes, Shape and Nature, London, 1652.
[Hartlib] Cressey Dymock, A Discoverie For Division o Setting out of Land, as to the best Form. … London, Printed for Richard Wodenothe in Leaden-hall-street, 1653.
Austen, R., A Treatise of Fruit-Trees shewing the manner of grafting, setting, pruning, and ordering of them in all respects… with the alimentall, and physical use of fruits. Togeather with the spirituall use of an orchard: held forth in divers similitudes, etc., Oxford, For Tho. Robinson, 1653.
Blith, W.,The English Improver Improved or the Survey of Husbandry Surveyed. … the Third Impression much Augmented, London, 1653.
Plattes, G., The Profitable Intelligencer, Included in Samuel Hartlib his Legacy, 3rd edition 1655 as Mercurius Lætificans.
Austen, R., The Spiritual Use of an Orchard; or Garden of Fruit-Trees. … Oxford, 1657.
Beale, J., Herefordshire Orchards, A Pattern For all England. Written in an Epistolary Address to Samuel Hartlib Esq., London, printed by Roger Daniel, 1657.
Austen, R., Observations upon some part of Sr F. Bacon’s Naturall History, as it concernes fruit-trees, fruits, and flowers, H. Hall for T. Robinson, Oxford, 1658.
Hartlib, S., The Compleat Husbandman: or, A discourse of the whole Art of Husbandry, London, 1659, (reissue of the second edition of Hartlib’s Legacy).
 Evelyn, J., Sylva, Or a Discourse of Forest-Trees, and the Propagation of Timber in His Majesties Dominions … Printers to the Royal Society, and are to be sold at their Shop at the Bell in S. Paul’s Church yard, 1664.
Austen, R., A Treatise of Fruit-Trees…Whereunto is annexed Observations upon Sr F. Bacon’s Natural History…The third impression, revised, with additions, etc., William Hall for Amos Curteyne, 1665.
Austen, R., A dialogue, or familiar discourse, and conference betweene the husbandman, and fruit-trees; in his nurseries, orchards, and gardens, etc., Oxford, printed by Hen. Hall for Thomas Bowman, 167.
Dymock, C., The New and Better Art of Agriculture, 1670.
Evelyn, J., Sylva, Or a Discourse of Forest-Trees, and the Propagation of Timber in His Majesties Dominions London, Printed by Jo. Martyn, Printer to the Royal Society, and are to be sold at their Shop at the Bell in S. Paul’s Church-Yard, 1679.
 Di Palma, V., “Drinking Cider in Paradise: Science, Improvement, and the Politics of Fruit Trees” in A. Smyth (ed.), A Pleasing Sinne: Drink and Conviviality in the Seventeenth Century England, Cambridge, Boydell and Brewer, 2004, 161-80, 165.