If you had the old Garden Utils Version 1.0 installed and then attempted to upgrade to Version 2.0 or later, the upgrade may not complete, leaving you with a half-installed app that may not be executable. This is probably because of App Store-related incompatibilities between the very old version and the new one, and iOS tries to prevent data loss.
If you have no files associated with the old version that you need to keep, you may uninstall the old app (which will delete the old data) and then redownload the upgrade.
If you wish to save the old files, connect your device to a personal computer with iTunes and use iTunes File Sharing to copy the files to somewhere on the personal computer, such as to a folder on the Desktop. You can then uninstall the old app (deleting the files from the device) and redownload and install the upgrade. If you still want the files to be associated with the app, copy them back in using iTunes File Sharing. For more information about iTunes Files Sharing, see Use iTunes to share files between your computer and your iPhone, iPad, or iPod touch (support.apple.com/en-us/HT201301).