Summers, from Notting Hill got 18 months, and Kadri, from Camden, two and a half years.
The judge, Mr Recorder Gopal Hooper, said: "In 2004 when you started upon this scam you were in good health, you were having a whale of a time living in luxury - no doubt beyond your means.
"This was done for greed not need - you wanted to continue to lead a lavish lifestyle.
"It was no doubt continuing your lavish lifestyle that you embarked with your two co-defendants in this scheme.
"You, Stuart Medhurst, were the leading light and that is something you admit."
Prosecutor John Traversi told the court that Medhurst spent more than £40,000 on electronics and household goods.
Medhurst had already admitted fraud in abusing his position at the RHS by withdrawing £43,895 for his own 'personal use'.
Summers and Kadri were each found guilty by a jury at the same court in July of one count of theft.
The fraud ran from January 2004 and January 2014. Medhurst worked for the RHS for 20 years and had an RHS flat in Westminster.
Traversi said: "In short the prosecution case is that Stuart Medhurst in collusion with Elaine Summers on the one hand and Shaheen Kadri on the other submitted false invoices prepared by Ms Summers and Mr Kadri for cleaning work that was never done.
"He arranged for payments by RHS to be made to bank accounts held by Elaine Summers at Barclays and by Shaheen Kadri at HSBC.
"When the money was received in those accounts, as far as Elaine Summers is concerned, it was then transferred to a NatWest account held by Stuart Medhurst with the deduction of the money that she earned by participating in this venture.
"As far as Shaheen Kadri is concerned the position as to what happened to the money when it entered his account is not so clear."RHS director general Sue Biggs said: "The RHS uses donations and funds from its supporters to enrich lives and improve horticulture and the environment across the UK.
"For someone to commit fraud and take money from a charity is deplorable.
"Today we're in a strong position to ensure unacceptable activity could not take place. The losses to the revenue of the RHS have been covered by insurance."