Let me get this straight...they are growing in your yard and they were not planted by you??? If this is the case and you are the legal homeowner it would be safe to say that you could either eradicate them (which I would not do) or next you could try and find out how they got there...Lastly, now I would never condone the jacking of plants that are not yours, however IMHO they are yours because they are on your property. I would really be careful though because if someone you dont know put them there they will be back for them (even though this would be entirely stupid of them). It might be in your best interest to just get rid of them or pull them and transplant them...and if you are interested in growing MJ, read a guide and possibly move it indoors...Good Luck, Peace Out and GG