what causes my small citrus trees leaves to be wavy

Question

I have grown them from seed and they are about 1 foot tall now. The leaves also have a sticky substance on them.

Answer 1

The sticky stuff is probably the honeydew excreted by aphids or scale insects. Here's some information on getting rid of them: https://www.gardeningknowhow.com/edible/fruits/citrus/controlling-citrus-scale.htm