From MCF:

Is the composter compatible with plants from Plant Mega pack? None of them seem to go in it.

As far as "Plant Megapack" is not available for 1.1x.x I could imagine integration of...
... Botania
... Mystical Agricultur/Magic Crops/Primordial Crops
in a more "magical" way (mana infused garden soil)

Non magic wishable Integrations could be:

• Natura/Forestry
• Biomes O' Plenty
  and else again
• Pam's Harvestcraft

Mods that exist, and add their own plants:

• RealWorld (The successor to plant mega pack)
• Rustic
• Roots
• Plants by Shadows_of_Fire
• Ice and Fire by Alexthe666
• Astral Sorcery
• Aquaculture
• Aether Legacy

There's probably some way to automate this, like looping through all registered blocks and adding anything that implements IGrowable or whatever the relevant interface(s) are.