The gardener has 1000 plants and wants to plant them in such a way that the number of rows and columns is the same, meaning the number of rows and columns must form a perfect square.

To find the nearest perfect square greater than or equal to 1000, we take the square root of 1000:

$\sqrt{1000} \approx 31.62$.

Rounding up, we get 32, meaning the gardener would need a square grid with 32 rows and 32 columns. The number of plants required for this is:

$32 \times 32 = 1024$.

The gardener already has 1000 plants, so the number of extra plants needed is:

$1024 - 1000 = 24$.

Therefore, the minimum number of extra plants the gardener needs is: