Wisdom of the Day 9: Mala hierba nunca muere
Buenos Dias familia,
Back again with another Wisdom of the Day for y'all. So, for those who don't know, in this thread, we will discuss the proverb or expression, your understanding, and its translation. 
I also noticed some have even offered phrases that serve as synonyms, THAT'S GREAT! As well, pictures are always welcome! 
Your participation is what makes this fun and keeps the learning locomotive running. 
19 Answers
One more try...A bad person just keeps showing up. You just cannot get rid of them. Evil seems to be outweighing good. It is like they are a bad seed or a bad penny. Every time you turn around, there they are again.
I promise. this is my last try, lol
Only the good die young.
Como soy una persona medio optimista, yo lo entiendo un poco diferente. Tal vez podemos verlo del lado positivo también... aunque no sea tan querida y cuidada como una planta casera chocha, una mala hierba nunca muere. Significa que a pesar de todos los obstáculos en su camino, que sea feita y rechazada, la mala hierba se pone fuerte y logra sobrevirir!
¡Qué viva la mala hierba!
Ji, ji, ji 
.
As quite an optimistic person, I understand it differently. Maybe we could see this from a positive angle as well... although it may not be as loved and looked after as a spoilt house plant, a weed never dies. This means that, in the face of many obstacles, be it ugly or unloved, a weed stays strong and managed to survive!
Long live weeds!
He, he, he
This seemed to be a tricky one, so I thought it would be something cool to provide some history, and the meaning intended. I hope y'all enjoy this as much as I did. Language is so interesting. 
"Hierba mala nunca muere" means always "Bad people last longer".
We all know the person who seems to break all the rules and get away with it. Perhaps they do, perhaps they don't, but perception is sometimes more potent than reality. This saying dates from the time when people had strong religious convictions and they were puzzled as to why some people appeared to get away with wrongdoing - hence the put-down of the Devil looking after them on Earth but hinting that they would get their comeuppance in Hell. 
If you have a good friendship you will probably call your friends bad stuff sometimes because everybody knows you don't actually mean it. That's one context where you can use that sentence, though like what's explained above it's not the real intended meaning of this proverb.
If y'all like this, and find it useful, I'll bring more to the table at the end of the challenge for that day after the answer is accepted.
I am going to go with (what think )would be literal.
"A bad weed never dies"
It's similar to the idea of the bad penny that always returns. Just when you think you've gotten rid of something, there it is again.
I guess it is the same concept as in the English phrase
"He/She always bounces back!"
"Weeds never die"
I think this may be more like Murphy's Law: if anything bad can happen, it will. It could also apply to how hard it is to break bad habits (and how easy it is to break good ones).
Literally, bad grass never dies.
There are species of grass that just keeps growing back no matter how many times & how short you cut them. They compete with the main crops for nutrients, water, & space, hence they are labeled bad. Applied to people, "bad grass" refers to those who just won't quit & have a never-say-die spirit, that no matter how difficult their struggles are & how many times they fall, they just keep coming back.
An English equivalent that comes to mind is:
When the going gets tough, the tough gets going.
I agree with cristalino: The devil looks after his own.
So DJ_H, kind of like the Devil takes care or watches over his own "kind" as it were? Those who appear to be getting away with all sorts of wrongdoing are like his "wards" or "charges"...they only prosper at their "iniquities" on account of ol' Satanas protecting them, more or less? 
Fortune favors the foolish.
This is what we say here in Poland, at least.
The cat came back. . .
I learn more about God
From weeds than from roses;
Resilience springing
Through the smallest chink of hope
In the absolute of concrete....
~Phillip Pulfrey, "Weeds," Perspectives, www.originals.net
Once a pain in the neck, always a pain in the neck???
Tengo en la punta de la lengua, pero no puedo pensarlo.
