Both the gardener and the landlord are responsible. There was a principal-agent relationship where both the principal and the agent are responsible for the agent's negligence. Also there may have arisen an "accord and satisfaction" by your landlord allowing you to deduct the cost of repair without protest. This is a legalize for saying the parties impliedly agreed that a claim was legitimate and was satisfied.
You do not say how long ago it was that the incident happened, nor do you state whether or not the landlord gave you any receipts for rent that might indicate his implied agreeement for the deduction. Certainly you have been disadvantaged by the landlord's failure to object to your deducting the loss if he had an objetion because there now may be a statute of limitations problem barring you from going against the gardener. If the landlord gave you any kind of receipt showing rent current after you deducted or even if he gave you oral indication that you were current, that would be implied consent to your deduction.
You now must take the landlord to small claims if he does not see it your way. And remember that the landlord must give you an accounting of the disposition of your security deposit within 21 days after you give back possession. If he fails to do this, he loses the right to deduct.