Does Much Needed Have a Hyphen?

In general, hyphens are joiners. Use them to avoid confusion or to form a single idea from two or more words: much-needed clothing (clothing is badly needed) versus much needed clothing (the clothing is abundant and needed). Do not use them in pairs to create an em dash.

Is it much needed or needed much?

Use the phrase as an adjective, and hyphenation is preferred. Use "needed" as an appositive (subjective complement) with "much" as a modifier, and it works with or without the hyphen.

How do you know if a hyphen is needed?

Generally, you need the hyphen only if the two words are functioning together as an adjective before the noun they're describing. If the noun comes first, leave the hyphen out. This wall is load bearing. It's impossible to eat this cake because it is rock hard.