Siam Queen Thai basil is unusual in that it is tropical in origin, so that means it thrives in lots of heat and sun. Given the room to grow, this basil plant forms an attractive rounded mound of narrow, pointed leaves, 18 to 24 inches tall and wide. Blue flower spikes appear later in the season than other basils which is a good thing, as the flavor of the leaves tend to deteriorate once the plant puts out flowers. Deer and rabbit don't like this scented, intensely flavored plant, so gardeners will be the only ones harvesting the leaves. Pick leaves as needed throughout the growing season, harvesting up to a third of the leaves at one time, but cut down the plant before freeze if you wish to dry the leaves for future use.