thank you! please help. Beekeepers advised to plant two seeds in the land together, Echium vulgare L and Melilotus to mix them together and plant in order to get a better production, and better growth. What does the Halacha say? is there a prohibition or not? please advise me in general where to read more basics about how to grow plants or apples and pick up apples.

The plants that you mentioned are weeds, and not for human consumption, and accordingly, there's no problem of kilayim [= mixing seeds]. Apple trees outside of Israel are very simple, just that they cannot be eaten the first 3 years (which are counted anew, every time the sapling was moved, if it wasn't transferred with its earth), and in the 4th year, can be eaten immediately (there are details how to count the years, but we'll keep it simple).