The lead offender, Jackson Ruwhiu, 18, of Kawakawa, struck Mr Lal over the head with a tyre iron and was sentenced by the Whangarei District Court in November last year to nine months' home detention.
Mr Lal described that sentence as a "joke" and is more angry at the four months' home detention handed down to Wharerau.
Wharerau and Ruwhiu both pleaded guilty to assault with intent to rob. The charge has a maximum penalty of 14 years in jail.
"They know they'll get home detention and money from [Work and Income] so they can sit at home and watch their Xbox. They won't work but they'll steal again perhaps somewhere else and the cycle will continue," Mr Lal said.
"Police are doing their job catching them but the courts need to toughen up. Hard labour is what these guys should be made to do rather than a holiday in prison," he said.
Mr Lal, who has run the dairy for 13 years, spent three days in hospital after being attacked with the tyre iron.
Wharerau's lawyer Wiremu Puriri said while he understood Mr Lal's position, the dairy owner needed to understand how the sentencing process worked.
The Matariki Court, he said, was not a soft option and normal sentencing guidelines applied.
Mr Puriri explained that as Wharerau's involvement in the attempted robbery was less than that of the lead offender he could not receive a higher sentence than Ruwhiu.
An early guilty plea, youth, and lack of previous convictions were taken into consideration by the Matariki Court during sentencing, Mr Puriri said.