In September 2018, Siteground announced that PHP 7.2 RC is available on all SiteGround servers. (Since November 2018, SiteGround supports up to PHP 7.3.)
PHP 7.2 has been officially released as of November 30, and it is now available for Siteground clients.
I contacted Siteground to check whether they offer the official version of PHP 7.2 or not. They said:
The 7.2 PHP version became an official one several days ago, and people are already moving their sites under it. In that regards - you can be confirmed that it is good to go.
It's possible to change PHP version to 7.2 or 7.3 from the PHP Version Manager tool in cPanel.
Currently, Siteground offers PHP 5.5, 5.6, 7.0, 7.1, 7.2 and 7.3. It's possible to apply a different php version to a WordPress installed on a sub-directory.
When using PHP 7.2 or 7.3, it is expected to bring some considerable speed, security and efficiency improvement.
This blog is currently hosted with Bluehost. In the VPS plans, PHP 7.2 is available
while PHP 7.0 is available in the Shared Hosting plans. (Now PHP 7.2 is also available on the Bluehost Shared Hosting accounts.)
Update in March 2019: SiteGround now supports up to PHP 7.3 and Bluehost supports up to PHP 7.2
If you sign up for a web hosting service by clicking on a referral link contained in this post, I will get some commission. However, I do not recommend a specific service just for commission. I've been using several webhosting services for years including Bluehost and SiteGround.
Most especially, if you sign up for Bluehost's Shared Hosting by clicking this link, you can use a Bluehost webhosting service with US$1/mo off starting from as low as US$2.95.