Mr Farron was quoted in the Mail on Sunday suggesting that the Lib Dem brand would be tainted for a generation by governing with the Conservatives.
Lord Ashdown said: "Tim's a very able guy but at the moment judgement is not his strong suit."
He was asked about Mr Farron's comments on Radio 5 Live's Pienaar's Politics.
The Lib Dem election campaign chief, and former leader, went on to say: "I know Tim very well. He is a great campaigner, a good friend of mine. I think his well-known ambitions would probably be better served with a little more patience and a little more judgement."
Mr Farron was quoted as saying: "In 2010, many people said: I am not voting for you because of the Lib Lab pact (in the 1970s) when I was seven years old. Just think what going into coalition with the Tories will do to our brand over the next generation."
The Lib Dems insist that was not a new quote.

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The 27-year-old, who tested positive for two anabolic steroids, broke into the British team last year, competing at the European Indoor Championships.
Wilson blamed a contaminated sample for her positive test.
UK Anti-Doping chief Andy Parkinson said: "This sends a strong message to anyone looking to dope in the UK."
Lincolnshire sprinter Wilson tested positive for banned steroids testosterone and clenbuterol after running the 100m in 11.95 seconds at the Bedford International Games on 12 June.
Wilson won the Commonwealth Games 100m trials in 2010 only to miss out on a place in the England squad due to not meeting the qualifying time
She issued a statement in July calling for UK Anti-Doping, who administer drug testing in the UK, to withdraw the case and open an internal investigation to determine the cause of the contamination.
However, an independent National Anti-Doping Panel upheld the European Indoor 60m semi-finalist's four-year ban.
"We have successfully argued for a four-year ban which demonstrates that UK Anti-Doping always seeks robust sanctions against athletes who look to cheat the system and betray those around them," Parkinson added.
"[It] gives clean athletes the confidence that we are working hard on their behalf, within the framework of the World Anti-Doping Code, to protect their right to compete in doping-free sport."
Spanish cyclist Alberto Contador tested positive for Clenbuterol during the 2010 Tour de France, which he claimed was a result of eating contaminated beef.
Clenbuterol, similar to the asthma drug salbutamol, is used to treat breathing disorders as a decongestant and bronchodilator. It causes an increase in aerobic capacity, blood pressure and oxygen transportation, and speeds the rate at which fats are burned.
It is officially classified as a sympathomimetic steroid.
Lord Ashdown has said Tim Farron - one of the frontrunners to be a future Liberal Democrat leader - lacks judgement.
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British sprinter Bernice Wilson has failed in her appeal against a four-year suspension handed out after a positive drugs test in June 2011.