Can you help me identify the big plant in the center right of the photograph? I planted a lot of different seeds but I don't think this is one of them, I think it's a weed.
Click photograph for full size
Definitely a weed - I must have pulled out thousands of these. If memory serves, they eventually produce small, pale pink flowers, and they prefer to grow where the soil is either uncultivated, or damp, or has poor drainage. I have never yet managed to work out precisely which plant it is though, hopefully someone else might know.