Compost is obtained by using the Composter, which needs 4000Organic Matter to make each Compost, excluding Composter Upgrades.
The following table gives the Organic Matter for all known compostable items. All Organic Matter values below are exact. For example, Potatoes are worth exactly 0.33 organic matter, not 1/3. Note that Tightly-Tied Hay Bales and Condensed Fermento can only be used with sufficient Composter Upgrades because they are worth more than the default limit of 40,000 Organic Matter.
Compost also has a 10% chance to drop from killing any Pest on ⏣ The Garden.
The best item to buy from the Bazaar for making Compost is currently Flowering Bouquet at 11,924 coins per 4000Organic Matter.
Lua Error: Invalid product ID "Hay Bale" stack traceback: [C]: in function 'traceback' Module:String:1825: in function <Module:String:1818> (tail call): ? (tail call): ? (tail call): ? mw.lua:527: in function <mw.lua:507> [C]: ?
➤ Template Error: Invalid product ID "Tightly-Tied Hay Bale"
Lua Error: Invalid product ID "Tightly-Tied Hay Bale" stack traceback: [C]: in function 'traceback' Module:String:1825: in function <Module:String:1818> (tail call): ? (tail call): ? (tail call): ? mw.lua:527: in function <mw.lua:507> [C]: ?
Compost Bundle, are used to unlock plots in ⏣ The Garden. Some Garden Visitors also request Compost. Compost' is also used with a 
Sprayonator to spray plots and attract Mosquitos and Earthworms.
Tightly-Tied Hay Bales and 
Condensed Fermento can only be used with sufficient Composter Upgrades because they are worth more than the default limit of 40,000 Organic Matter.
Flowering Bouquet at 11,924 coins per 4000 Organic Matter.
Geonathan Greatforge and 
Jotraeline Greatforge request Compost when visiting in ⏣ The Garden
32
Added Compost.