Rummi, so you live in New Zealand!* I figured you might be in the UK or from another country and here in the US.* Just goes to show what a small world we've become.*
There are several knowledgeable folks at the UBC Botanical garden site from tropical countries.* I don't know if they grow many veggies, but I've seen them answer lots of questions about tropical plants.* Do you mind saying where you will be going?
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.