[1] He developed an interest in botany and horticulture as a child, and by his teenage years was friends with some of the most eminent botanists, horticulturists and landscapers of the day, including; Philip Miller, keeper of the Chelsea Physic Garden, Philip Southcote, a leading pioneer of landscape design, and Peter Collinson, the Quaker haberdasher turned horticulturist who was to remain a lifelong friend and colleague.
Now in complete control of Ingatestone and Thorndon halls, Robert was able to give full expression to his enthusiasms and immediately embarked on an ambitious plan to remodel both the house and the park, which had been held in trust for him since his father's death.
The Great Stove, reputed to be the largest hothouse in the world, was fully 30 feet (9.1 m) high and contained trees and shrubs 10 to 25 feet (7.6 m) tall including specimens of guava, papaw, plantain, hibiscus, Hernandia (jack-in-a-box), ceroid cacti, sago palm, annatto (a red berry used for edible dye) and bamboo cane.
There were also two other stoves maintained at a slightly lower temperature for more temperate plants, a house 60 feet (18 m) long exclusively for the cultivation of bananas and pineapples and another the same size for storing apples.
From these stoves came the first camellia to flower in England and, in 1739, a gift of bananas sent to Sir Hans Sloane (along with "2 uncommon fowls of the widgeon kind").
Nonetheless, there were failures too; Robert was particularly fond of the white lilac and, on one occasion, culled sufficient seed to raise in his nursery 5,000 new plants.
By 1762, however, Collinson, on a visit to Thorndon, found a scene of desolation: the house was falling down, the nurseries overgrown and the stoves empty, apart from two date palms, a cactus and a few sickly shrubs.
The redesign of the estate by his son swept away much of Lord Petre's work, only traces of the plantings, the two mounts adjacent to the present house and the ruins of the ziggurat by the old mill pond can be found today.
When Robert was 18, he was elected a fellow of the Royal Society – not in itself an exceptional honour since peers of the realm had an automatic right to membership but it is a mark of the esteem in which he was already held that his sponsor was John Martin, future professor of botany at Cambridge.
Furthermore, less than two years later, a Caribbean genus of the verbena family, which the plant collector, Dr. William Houston had identified, was named Petrea in Robert's honour.
On his death, the following poem, signed by Janus the Younger (probably a pseudonym for Philip Southcote), appeared in the Daily Advertiser: Ye lilies rise, your sweets disclose.
[3] The monument represented an angel blowing the last trump causing a stone pyramid to crumble to pieces and the corpse within it to throw aside the grave clothes and prepare to arise "with a mixture of joy and astonishment".
This stone, ennobled by a PETRE's name Changes its nature and becomes a gem, Bright with the virtue which appear'd in him: bearing his name, it bears all moral good, And all the ancestry of blood: The saint, the friend, philosopher, and peer In all their lustre to your eyes appear Perusing PETRE only written hereOver the door of the temple, were further verses written by Robson, warning the reader to prepare for death.