Soil & potting mix
Best soil for Million bells (Calibrachoa × hybrida)
Also called Million bells, Mini petunia, Trailing petunia.
More about million bells
About Million bells
Calibrachoa × hybrida · also called Million bells, Mini petunia · flowering
Million bells is a prolific trailing annual producing hundreds of small petunia-like flowers in a vast range of colours from spring through autumn frost. Self-cleaning and vigorous, it excels in hanging baskets, window boxes, and container edges. It demands excellent drainage, regular feeding, and full sun to maintain its non-stop floral display.
Preferred mix: Well-draining, slightly acidic compost or potting mix, pH 5.5–6.0
Watch for — Iron/magnesium chlorosis (yellowing between veins): The most common issue; caused by pH above 6.2, waterlogged roots, or insufficient feeding. Lower pH with ericaceous feed, improve drainage, and apply iron chelate or Epsom salt (magnesium sulphate) foliar spray.
Why million bells needs this mix
Million bells is a true acid-lover — it physically cannot take up iron above about pH 5.5, so an ericaceous mix is not optional, it is survival.
- Million bells has evolved on acidic, peaty ground and depends on soil fungi that only function in acid conditions — raise the pH and it starves even in "rich" soil.
- In a too-alkaline mix iron and manganese lock up chemically, so the youngest leaves yellow between green veins (lime-induced chlorosis) and the plant fades out.
- Its fine, shallow roots also want an open, free-draining structure, not a heavy clay or claggy compost.
For the full picture on what makes up a good mix, see our guide to the main types of soil and potting media — it explains why each ingredient above behaves the way it does.
What goes wrong with the wrong mix
The wrong soil is one of the most common reasons million bells struggles, and the damage often shows up weeks later as a watering problem. For this species specifically:
- Ordinary multipurpose or garden compost is far too alkaline for million bells — expect classic yellowing, weak growth and a slow decline over a season or two.
- Hard tap water slowly pushes the pH up too, undoing a good mix; rainwater is strongly preferred for watering.
- Lime, mushroom compost or wood ash anywhere near this plant is actively harmful.
Planting million bells in standard compost or limey garden soil. Without an acidic (ericaceous) medium it will yellow and fail no matter how well you water and feed it.
pH — does it matter for million bells?
This is the whole game: Million bells needs pH 4.5-5.5. Test it, use ericaceous compost (and an ericaceous feed), and water with rainwater where you can to keep the pH from creeping up.
If you want to check or adjust it, the soil pH guide walks through testing and the safe ways to nudge a mix more acidic or more alkaline.
DIY mix vs a bagged one
Bagged ericaceous compost is the correct, easy base for million bells; just open it up with bark and grit per the ratio above. Do not try to acidify ordinary compost by guesswork — it rarely holds.
Drainage and the pot
Containers are often easier than open ground because you control the pH completely. Use a pot with good drainage and an ericaceous mix; never let it sit waterlogged.
Top up or refresh the ericaceous mix yearly and test the pH each spring — it naturally drifts upward over time, especially if watered with tap water. When the time comes, our repotting guide for million bells covers the timing and technique step by step.
Million bells soil — frequently asked questions
What is the best soil mix for million bells?
3 parts ericaceous (acidic) compost : 1 part composted pine bark or pine needles : 1 part perlite or coarse grit. Million bells has evolved on acidic, peaty ground and depends on soil fungi that only function in acid conditions — raise the pH and it starves even in "rich" soil.
Can I use normal potting soil for million bells?
Ordinary multipurpose or garden compost is far too alkaline for million bells — expect classic yellowing, weak growth and a slow decline over a season or two. Bagged ericaceous compost is the correct, easy base for million bells; just open it up with bark and grit per the ratio above. Do not try to acidify ordinary compost by guesswork — it rarely holds.
Does million bells need a special pH?
This is the whole game: Million bells needs pH 4.5-5.5. Test it, use ericaceous compost (and an ericaceous feed), and water with rainwater where you can to keep the pH from creeping up.
Should I buy a bagged mix or make my own for million bells?
Bagged ericaceous compost is the correct, easy base for million bells; just open it up with bark and grit per the ratio above. Do not try to acidify ordinary compost by guesswork — it rarely holds.
How often should I refresh the soil for million bells?
Top up or refresh the ericaceous mix yearly and test the pH each spring — it naturally drifts upward over time, especially if watered with tap water. Containers are often easier than open ground because you control the pH completely. Use a pot with good drainage and an ericaceous mix; never let it sit waterlogged.
Keep reading
- Million bells care — the full brief (light, water, humidity, problems, pet safety)
- How often to water million bells — the schedule the mix feeds into
- Repotting million bells — when and how to refresh the mix
- Soil pH guide — test it and adjust it safely
- Root rot — how the wrong soil starts it, and how to save the plant
- Underwatered plant — signs and how to rehydrate it
- Should I water my plant? The simple check first
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- All 6887 soil and potting-mix guides in the Growli library