In games where you cannot buy gardens, you do not have a negative infinite amount. You have a 0 amount. Zero and negative infinity are very different numbers.
For some further fun, let's figure out the net point effect of any negative-valued gardens.
Worth 1 for every 10 cards in your deck (rounded down)
If I have 10 cards in deck, each would be worth 1 (10/10 rounded down). Net of 10 * 1 = +10 points.
If I have 1 card in deck, each would be worth 0 (1/10 rounded down). Net of 0 points.
If I have 0 cards in deck, each would also be worth 0 (0/10, rounded down). And I have 0 of them, so it's still a net of 0 points.
If I have -1 cards in deck, each would be worth -1 (-1/10, rounded down). But I have -1 of these -1 value cards, so I actually have -1 * -1 = +1 points.
If I have -10 cards in deck, each would also be worth -1 (-10/10, rounded down). But I have -10 of these -1 value cards, so I actually have -10 * -1 = 10 points.
If I have -11 cards in deck, each would be worth -2 (-11/10, rounded down). But I have -11 of these -2 value cards, so I actually have -11 * -2 = 22 points.