The Compost Machine in Build a Ring Farm turns spare seeds into a single random reward. You feed seeds into it, climb through Compost tiers based on the total Cash value you deposit, then pull a lever to roll three prizes and keep one. The higher the tier, the better and rarer the possible rewards, which is why the machine becomes a steady source of mutation sprays and fertilizers as your farm grows.
Where to find the Compost Machine
The Composter sits on the sides of the second and third floors of your ring farm. You unlock these floors by spending Cash on farm expansions until the upper levels become accessible. There is no separate quest or code involved. The machine simply appears once the relevant floor is built out.
The third-floor Composter offers higher odds of rolling rarer rewards than the second-floor version. Because of that difference, it is worth saving your most valuable seeds until you have finished your expansions and can use the third-floor machine.
How to use the Composter
Step 1: Walk up to the Compost Machine on the second or third floor and hold the E key to open its menu.
Step 2: Press the "Add Plants" button and select the seeds you want to sacrifice. The machine tracks the combined Cash value of everything you deposit.
Step 3: Keep submitting seeds until the total value reaches the threshold for the Compost tier you want. Each tier unlocks once its minimum value is met.
Step 4: Press "Pull Lever." The machine rolls three reward options from that tier's pool, and you choose a single item to keep.
You know the pull worked when the three reward choices appear on screen and your selection lands in your inventory. If the lever will not produce a roll, you have not yet deposited enough seed value to reach a tier. The only requirement is hitting the Cash value threshold, so add more seeds and try again.
Compost tiers and seed value requirements
Tiers are gated by the total Cash worth of seeds you submit. Reaching a higher tier costs far more seed value but improves the reward pool. To climb quickly, buy and submit high-value Exotic and Transcended seeds.
| Tier | Seed value required |
|---|---|
| Unranked | Unlocked by default (starter tier) |
| Rich Compost | 5 billion Cash |
| Prime Compost | 50 billion Cash |
| Overgrown Compost | 25 trillion Cash (current max tier) |
Rich Compost rewards and drop rates
The first major tier draws from four rewards. Super Fertilizer is the most common pull, while the 2x Strong Fertilizer roll is the rarest.
| Reward | Image | Chance |
|---|---|---|
| Super Fertilizer |  | 40% |
| Void Spray |  | 30% |
| Super Pet Treat |  | 22% |
| 2x Strong Fertilizer |  | 8% |
Prime Compost rewards and drop rates
Prime Compost shifts the pool toward stronger items. Void Spray becomes much more likely here, and two reward types are exclusive to this tier and above.
| Reward | Image | Chance |
|---|---|---|
| 2x Super Fertilizer | 50% | |
| Void Spray | 45% | |
| Radioactive Spray |  | 4% |
| Compost Hydra |  | 1% |
The Compost Hydra is exclusive to the Composter, so this machine is the only place to get it.
Overgrown Compost rewards
Overgrown Compost is the current top tier and unlocks the highest-end sprays. Its exact roll rates scale with the total seed value you submit rather than a fixed percentage, so larger deposits push the odds toward the better items.
| Reward | Image |
|---|---|
| Radioactive Spray | |
| Cosmic Spray |  |
| Rainbow Spray |  |
| Super Pet Treat | |
| Super Fertilizer |
Which reward to choose
Since you pick one of three rolled options, knowing what each item does helps you choose fast. Void Spray is the standout at the Rich and Prime tiers because it applies the Void mutation, which multiplies a crop's value. Save it for your best, highest-value plants and a big sale rather than using it on weak crops.
Super Fertilizer is the workhorse reward. It speeds up the planting and harvesting loop, which matters most for new and mid-game players who are still building income. Super Pet Treat is worth taking if pets are part of your setup, since it boosts pet progression. The 2x Strong Fertilizer roll is the rarest at the Rich tier, but it is situational and usually loses out to a mutation spray for long-term profit.
Best way to run the machine
Treat the Composter as a long-term bonus rather than a jackpot. Feed it spare seeds whenever you have extras, and let the rewards accumulate over many pulls. A few simple habits keep the value high.
- Submit cheap or surplus seeds for value, and save expensive crops unless the reward chance justifies them.
- Hold valuable seeds until you can use the third-floor machine or a higher tier.
- Bank every Void Spray for your strongest plants instead of using it right away.
- Use Super Fertilizer during active farming sessions to keep the loop moving.
Run regularly, and the Compost Machine steadily converts leftover seeds into fertilizers, pet treats, and mutation sprays, including items like the Compost Hydra that you cannot get anywhere else.