Technically, no. You can start a blog and run the blog without an SSL certificate. But the trends are showing that Google and maybe other search engines tend to prefer websites that have an SSL certificate installed.
This includes blogs. But you can install an SSL certificate later after starting your blog if you feel like you need it.
You will need an SSL certificate if you offer items for sale and are collecting sensitive information from your customers.
From a visitor’s perspective, the SSL certificate allows people to see the small “green lock” on their browser which indicates that the website they are visiting is generally safe when they submit sensitive information.
Most blogs do not need an SSL certificate, but if you can afford it you might as well get it. It probably plays as a positive factor into Google’s rankings, and likely it will do so more in the future.