The 23-year-old 6ft 3 in striker joined Reading in July 2015 after scoring 22 goals for non-league Billericay Town.
He then ended last season on loan to League Two side Wycombe Wanderers.
He failed to score in his 10 games for the Chairboys, in which their only win was against Stevenage.
"We are determined to add strikers to the backbone of the side that finished strongly defensively last season," said Stevenage chairman Phil Wallace.
"Rowan is an exceptional athlete and a big lad, but the step from non-league to the Championship is a huge jump for an inexperienced young player. He'll need time to evolve."
Stevenage have also signed left-back Andrew Fox from Peterborough United and Ebbsfleet striker Matt Godden.
Boro have also signed keeper Jamie Jones on a more permanent basis, having kept six clean sheets in 17 games last season on loan to Darren Sarll's side from Preston.
Find all the latest football transfers on our dedicated page.
Stevenage have made their third new signing by bringing in striker Rowan Liburd from Championship side Reading for an undisclosed five-figure fee.