If a premise is incoherent, is the conclusion invalid?

If a premise is incoherent, is the conclusion automatically invalid?

Coherent premise : "Dogs have 4 legs", "Cats are not dogs", "Houses are over 5' tall", etc
Incoherent premise : "Blue is greater than 10", "Apples are oranges", 2+5=78, etc 

If the question means "If one can't understand the premises, should one believe the conclusion?", then the answer is "Maybe!"  However, there would need to be some other reason to believe the conclusion since the premises wouldn't be convincing.

For the argument to be valid, the conclusion must follow from the premises – otherwise, we're looking at a non sequitur making the argument invalid.  If all premises are true and if the premises create an uninterrupted pathway to the conclusion, the the argument is valid and the conclusion would be true.  However, if premises are not true (as with some of your examples above) or if they simply don't make sense or aren't related to the conclusion, then the logic falls down and the conclusion comes into question.

Often, incoherent or confusing premises can be used to confound one's audience either in an attempt to confuse or simply be unclear (ambiguity fallacy) or in an attempt to baffle the listener with high-sounding statements rather than facts (argument by gibberish).

Of course, we also need to remember that even though all premises may be false, the conclusion just might be true anyway ... even if it doesn't follow logically from the premises.  For example:

Premise 1:  The intrinsic nature of emotions can often obfuscate natural realization of etymological manifestations.

Premise 2: The sky is actually green – we've just been conditioned to call it blue.

Conclusion:  Therefore, Thursday follows Wednesday each week.