You are being rude, not your dil.
"Being polite costs nothing" you wrote.
Start practicing it.
Your son and dil are not on the same page.
They both have to agree on what they would like you to do, not just your son.
Help is what the people receiving it consider help, not the party giving the help.
Do you understand the difference?
You are not helping.
You are intruding, overstepping and being overbearing.
These are two adults who can manage their lives independently, they don't need you
The garden is not high on their list of priorities. Your own son could do it himself if he thought a tidy garden is so important.
The garden is high on your list of priorities.
Who has the call here? THEY do. Their garden, not yours.
Your dil had a huge husband problem. Your son is picking his comfort and your wants over his wife.
Your comments clearly show enmeshment on your son and your part.
It is not going to end well if this continues.
If your son doesnt change, he will see his child every other weekend + 1 afternoon a week - or the standard visitation offered in your area.
Your dil has been very polite so far.
One day, she is rightfully going to explode.
I wonder how she has letting this go for so long