My question is, how could I have negotiated to go on gardening leave?

You almost certainly couldn't have done. This is always going to be tough, since you haven't got a lot of cards here - you've already announced that you're leaving, and you may still need a good reference from your existing employer in the future (so burning bridges gives you no real benefit.)

Gardening leave, especially the "stop work altogether" kind, isn't something that's typically negotiated. It's generally mandated by companies that are worried disgruntled, soon to be ex-employees may decide to leak or sabotage company data / operations. In some cases more than others (think large hedge funds / banks), the cost of paying someone's salary in their notice period is nothing compared to the potential billions in damages a disgruntled employee could cause.

It should go without saying, but definitely don't try to use the above as a negotiating tactic. Going along the lines of "But if you keep me around I might deliberately screw everything up just for the hell of it" is a fast way to get the lawyers involved, a possible criminal record and no chance of ever getting a good reference.

If you're determined to go ahead and negotiate the "work from home" kind, then like any negotiation, concentrate on the potential plus points to the employer:

• If you feel other people are giving you a hard time / cold shoulder because you're leaving, then you'll be more relaxed and able to do better work at home;
• If people are asking you lots of questions because you're leaving about handover, etc. then you can also get on with your work more effectively if they're forced to send those via email instead;
• (Any other potential other benefits of home working in general.)

Honestly, the above are really quite weak points though - it's unlikely your employer will be willing to let this happen unless it's something they were planning anyway.

My question is, how could I have negotiated to go on gardening leave?

You almost certainly couldn't have done. This is always going to be tough, since you haven't got a lot of cards here - you've already announced that you're leaving, and you may still need a good reference from your existing employer in the future (so burning bridges gives you no real benefit.)

Gardening leave, especially the "stop work altogether" kind, isn't something that's typically negotiated. It's generally mandated by companies that are worried disgruntled, soon to be ex-employees may decide to leak or sabotage company data / operations (or potentially steal clients - as per the comment.) In some cases more than others (think large hedge funds / banks), the cost of paying someone's salary in their notice period is nothing compared to the potential billions in damages a disgruntled employee could cause.

It should go without saying, but definitely don't try to use the above as a negotiating tactic. Going along the lines of "But if you keep me around I might deliberately screw everything up just for the hell of it" is a fast way to get the lawyers involved, a possible criminal record and no chance of ever getting a good reference.

If you're determined to go ahead and negotiate the "work from home" kind, then like any negotiation, concentrate on the potential plus points to the employer:

• If you feel other people are giving you a hard time / cold shoulder because you're leaving, then you'll be more relaxed and able to do better work at home;
• If people are asking you lots of questions because you're leaving about handover, etc. then you can also get on with your work more effectively if they're forced to send those via email instead;
• (Any other potential other benefits of home working in general.)

Honestly, the above are really quite weak points though - it's unlikely your employer will be willing to let this happen unless it's something they were planning anyway.