think about it like this:

85% of all genetic material in ALL human's DNA in included in our each of us. Even if you don't look dark, the DNA is there, recessively.

if a plant can't handle the cold, it dies. but it's brother, not too far way, grown from a seed which dropped from the same plant as the dead one, lives because the hearty cold gene is dominate.

plant vigor is based on its environment, assuming it is genetically healthy. evolutionary adaptation takes place on too long a time scale for anyone to see with their eyes, so far as we know.

for example: records show people today live longer and are taller and bigger then the past (thousands of years ago even). is this evolution? no. it is medical and diet awareness that are creating a healthy generation that are reaching their FULL POTENTIAL for body size and mass. like giving a plant everything it needs will create a 'monster'. really, any healthy plant could acheive that with the same care.