HOW DO I STOP SPAM posting on blog

Send comments to moderation. The codex suggest several solutions. https://codex.www.ads-software.com/Combating_Comment_Spam

do you have captcha? Simply requiring a valid email for comments or requiring site registration will help but you’ll still get a lot of spam without captcha.

Captchas are useless and cause more problems than they solve.
https://blackwidows.co.uk/blog/?s=captcha

Maybe so, but it cut my spam by about 90%. I was getting flooded otherwise.

Generally, activating Akismet and keeping it updated is the way to go. This works well for most of my clients, but it never cuts 100% of comment spam. Still, it does a pretty good job.

Captcha may lead to less spam, but not every person wants to fill it out either, so less people may comment as a result… if having lots of comments is your goal, I’d never run a Captcha.

I agree on the utter pointlessness of Captchas…

Having said that I don’t get much spam. Which may be due to:

Akismet
Antispam Bee
Growmap Anti Spambot Plugin
http:BL WordPress Plugin
Project Honey Pot Spam Trap
[ And installing my own Honey Pot ]
Spammer Blocker
Select TimesToCome Stop Bot Registration
WP-BlackCheck

Exploit Scanner
Health Check
WP Security Scan

And not a plug-in: installing zbblock.

Or it may be due to pure luck.