Bonsai annuals are fun, easy, and not much investment to lose of you mess up. By July the garden shops' starter plants are often already started miniaturizing their leaves, you can often pickup a bunch of "damaged" plants for free. Leave them in the nursery pots and keep 'em alive and you can get awesome results.<p>Peppers, tomatoes, and hemp all work well that way. Tomatoes can make fruits bigger than the plant, if you torture them right.<p>Cucumbers are lovely as minis but are much harder to keep contained and harder to get to fruit. They grow their fruit too fast and its hard to get enough water into the plant without drowning it.<p>Tobacco was entertaining to grow in a small pot, i got a 6ft plant that flowered in a 1L pot. it never had great leaves and it scavenged nutrients out of lower leaves to grow higher ones so it was all spindly. Never "miniaturized" the way other plants do. I suspect pumpkins and some other families would behave the same way.