At its core, this is basically a collection of resource packs from Vanilla Tweaks (Fully Aged Crop Marker, Fully Aged Amethyst Cluster Marker, and Age 25 Kelp), but I've modified them to support modded crops and resources, so full credit for this goes to that team. This resource pack adds a marker above crops that are ready to harvest. For most crops this is a bouncing exclamation mark, but with kelp it is a flower. This includes all vanilla crops and crops from the following mods:

• Oh the Biomes You'll Go
• Immersive Engineering
• Mystical Agriculture
• Pam's Harvestcraft 2 - Crops
• Silent Gear
• Thermal Cultivation 
• Farmer's Delight 
• Croptopia New in version 4
• Bewitchment New in version 5
• Promenade New in version 5

Version 5: The Crystal Expansion

With the release of version 5, alerts have been added for fully grown amethyst clusters, as well as crystal clusters added by the following mods:

• Oh the Biomes You'll Go (Ametrine Ore, Subzero Crystal)
• Spectrum (Topaz, Citrine, Onyx, Moonstone)
• More Geodes (Emerald, Quartz, Diamond)

To Do:

• Alert for croptopia corn
• Alert for cocoa beans

Credits:

Vanilla Tweaks: https://vanillatweaks.net/