Quick answer
Starred crops do not automatically upgrade after enough planting cycles. A specific crop needs enough successful growth steps.
Current game data shows that for 
Cabbage, 
Onion, 
Pumpkin and 
Grapes planted from 1★ or 2★ seeds, the next quality starts appearing from the 11th successful step.
Key fertilizers:
Each bed has at most two fertilizer slots.
Why does crop quality feel random?
A crop is graded by successful and failed steps.
Every planting has:
four planting steps;
automatic growth steps afterward;
successes and failures.
Those successes determine:
yield;
seed return;
whether starred crops upgrade.
Two beds using the same seeds can therefore produce different results if their skill or planting quality differs.
Farming Mastery only matters while planting
This is the key rule.
Your Keeper's Farming Mastery matters during planting.
After planting, the bed's own skill controls growth.
That means:
eating a
Muffin after planting does not improve the existing crop;
equipping a better rod later does not help it;
buying a Farming talent halfway through growth does not fix previous failures.
Prepare Mastery before planting.
Starred crop requirements
Cabbage
1★ — Farming 8
2★ — 10
3★ — 12
Onion
Pumpkin
Grapes
Planting below the requirement is possible, but some planting swings can fail.
Those lost successes remain lost for that crop.
How growth works after planting
A normal crop has 12 total steps.
The first four are planting steps, leaving eight automatic growth steps.
Each growth tick compares bed skill with the crop requirement.
Skill >= requirement
The tick succeeds.
If skill is double or triple the requirement, it can complete multiple steps at once.
Skill < requirement
The crop still advances, but that step has a chance to fail.
The important consequence:
low skill mainly reduces yield and quality rather than simply making crops slower.
How star upgrades work
The current game-data formula shows the next star level for 1★ and 2★ crops beginning at:
11 successful steps
A 2★ Grape crop with only 9 successful steps will stay 2★.
A crop reaching 11–12 successful steps can produce 3★ Grapes and 3★ seeds.
So the real goal is to make enough of the 12 steps succeed.
Peat
Peat is the first fertilizer.
Recipe:
8 Leaves
→ 2 Peat
Effect:
bed skill +1
It is useful early, but +1 alone is not enough to solve the highest starred crop requirements.
Peat also becomes the base ingredient for stronger fertilizers.
Crop Boosting Fertilizer I
Recipe:
2 Peat + Dream Dust
→ Crop Boosting Fertilizer I
Effect:
+2 crop steps
The crop takes two additional steps to finish.
If your skill is strong enough, that means:
another crop;
another seed;
more opportunities to cross the star-upgrade threshold.
This is powerful when the bed already has reliable success chance.
Farming Fertilizer I
Recipe:
2 Peat + Weak Growth Elixir
→ Farming Fertilizer I
Effect:
bed skill +2
Use it when failures are the real problem.
Farming Fertilizer II
Recipe:
4 Peat + Rich Growth Elixir
→ Farming Fertilizer II
Effect:
skill +3
A strong mid-game option for advanced vegetables and Grapes.
Farming Fertilizer III
Recipe:
8 Peat + Miracle Growth Elixir
→ Farming Fertilizer III
Effect:
skill +5
This is the strongest normal skill fertilizer and is especially useful for 3★ crops.
Headstart Fertilizer
Headstart does not raise skill.
It provides guaranteed successful steps immediately.
Headstart I
+1 guaranteed step
Headstart II
+2 guaranteed steps
This is excellent when you are close to the 11-success threshold but occasionally lose one or two growth ticks.
Maximum fertilizer slots
Fertilizers I unlocks the first slot.
Fertilizers II unlocks the second.
The normal current farming system has two slots maximum.
Do not delay progression waiting for a mysterious third fertilizer slot.
Good combinations
Stable basic farming
Farming Fertilizer + Peat
Raise skill.
Star upgrading
Farming Fertilizer + Headstart
A safe quality-focused combination.
High-skill bed
Crop Boosting + Headstart
Adds total successful-step potential and yield.
Late quality farming
Use 
Farming Fertilizer III plus Headstart or Crop Boosting depending on the bed's natural skill.
Garden upgrades
Base 
Garden Bed:
skill 2
Garden Upgrade I:
skill 4
Garden Upgrade II:
skill 8
That change is enormous.
Trying to force late 3★ crops on the original skill-2 garden using fertilizer alone is much harder than upgrading the garden itself.
Vineyard Upgrade
A normal 
Vine Trellis has:
skill 6
Vineyard Upgrade raises it to:
skill 11
Grapes still ask for:
So fertilizers remain relevant even after fully improving the Vineyard.
Why doesn't Vineyard Upgrade speed things up as expected?
In the current build, part of the advertised speed behavior is not functioning the way the text suggests.
The important reliable effect is the increase to trellis skill.
Treat it primarily as a yield/quality upgrade.
Are fertilizers permanent?
Current game-data analysis indicates that fertilizer should remain on the bed after harvest and only be replaced by another fertilizer in that slot. The database marks this detail as code-derived and not yet fully verified in play, so it is worth rechecking after future patches.
Do not manually apply the exact same fertilizer again while it is already present; the item can be consumed without adding another copy of the effect.
Can Farming Fertilizer +3 and +5 stack?
Yes. They are different fertilizer tiers, and current-build player reports confirm that they can occupy the two unlocked slots together.
But calculate the skill first. A fully upgraded Vineyard trellis already has skill 11; +5 raises it to 16, enough for 3★ Grapes. At that point another +3 does not improve the success chance, so 
Headstart II or Crop Boosting is usually a better second slot.
How to get 3★ Grapes reliably
A good route is:
- 1
- 2
- 3
prepare Farming Mastery before planting;
- 4
- 5
- 6
add Headstart or Crop Boosting;
- 7
reach at least 11 successful steps;
- 8
harvest the first 3★ seeds;
- 9
If you only need 3★ 
Wine urgently, there is a faster shortcut with 
Spices and 
Umami.
See How to Get Gold-Star Wine.
Zombies and crop quality
Zombie gardeners use their own Farming Mastery.
Once a zombie claims a bed for its crop order, your Keeper no longer has the same manual control over that bed.
For exact quality farming, keep at least a few beds or trellises for manual use until the zombie setup is strong enough.
Why am I losing seeds?
A weak crop can return fewer seeds than the four you planted.
A perfect standard 12-step crop gives:
That means +2 seeds net.
If your seed inventory shrinks every cycle, your success count is too low.
FAQ
Why does a 2★ seed give 2★ crops again?
The crop did not reach 11 successful steps.
Does Farming Mastery affect the entire growth cycle?
No. It matters during planting; the bed skill handles growth afterward.
How many fertilizer slots are there?
Two.
Headstart or Farming Fertilizer?
Use Farming Fertilizer when skill is low. Use Headstart when you are already close to the success threshold.
Does Crop Boosting make the plant faster?
No. It adds two growth steps and increases potential output.
Can I make 3★ Wine without 3★ Grapes?
Yes, by upgrading Wine with Spices and Umami.
