Books

@Purple Streaks This one is quite good, and most definitely safe:
Internet Archive Search: gardening

They also have other kinds of media, like videos and audio.
In general, they collect and offer for free material which is either out of copyright or has been donated by publishers and other providers.

The site you link (Manybooks) is also in part a collection of out of copyright material (Jack London, Edgard Allan Poe and so forth), the rest are cheap books which they try to sell.
Given all quality books they offer are available on the internet elsewhere, normally without the need of creating an account and share your email, I would not use Manybooks.
Also, at 50,000 free books, their offer is very limited and available elsewhere, including the two sites below:
Archive.org offer 25 millions books.
Gutenberg.org offer 60,000 only, but normally in kindle format (Mobi format) and downloadable with no requirement to create an account.

 

Thanks Aldo,yes these which you mention look promising!I shall look into them .