No, sehen is the correct form for sie = “they”. Seht is used if the subject is ihr (plural “you”)
However “to look at” is ansehen in German, so “they look at the flowers” would be: Sie sehen die Blumen an. (an is a separable prefix that’s why it gets detached from the verb; separable prefixes are almost certainly a part of later skills)
Doesn’t “bloom” specifically refer to the blossom part of a larger plant though? This would be a Blüte in German. A Blume is more than just a bud, it’s a bud on a stalk which normally grows directly from the ground. There is a little leeway on the last point, for example with roses, but even there I would be inclined to talk about a Blüte when I see the whole bush instead of just a single stalk cut from the bush.