Melons

Some of my melons were planted in the floor of the greenhouse, and aren't growing nearly as well as the two I planted into pots. Could it be lack of light as there is a large nettle and a comfrey plant right outside reaching to about 3'?
The potted ones have produced female flowers. Maybe I'll get a melon this year.....

 

Not my area of expertise but, light may me an issue, and ground temperature may be affecting growth too ?

 

Also, if the ones in pots are in compost then they are getting more nutrients. The nettle and comfrey are not helping either as they are leaching water and nutrients from the soil. David.