Quick answer: As a working guide, five plants in a 30cm basket, seven in a 35cm and nine to twelve in a 40cm, including side planting. Vigorous trailers need fewer, compact plants need more, and overplanting is what causes a basket to collapse in midsummer.
The question every garden centre queue is silently working out, and the answer varies more than the guides suggest.
The working numbers
| Basket diameter | Plants, roughly |
|---|---|
| 25cm | 3 to 4 |
| 30cm | 5 |
| 35cm | 7 |
| 40cm | 9 to 12 |
| 45cm and above | 12 to 15 |
These include side planting where the basket allows it - the buyer's guide covers choosing the basket itself.
Why the numbers vary so much
Because plants differ enormously in how much space they fill.
A vigorous trailing petunia will cover a third of a basket on its own. A compact lobelia covers a fraction of that. Using the same number of each gives you a crowded basket in one case and a sparse one in the other.
The label's eventual spread is the number to look at, not the pot size - the flowers guide covers the varieties worth using.
What overplanting actually does
Not much in June, which is the trap. An overplanted basket looks magnificent immediately, which is exactly why people do it.
The problems arrive in July and August. Roots compete for a small volume of compost, the basket dries out faster than anything can keep up with, plants shade each other, and flowering drops off. By late summer an overplanted basket is usually the tired-looking one.
What underplanting does
Looks thin for a month, then fine. Plants fill the space they are given, and a slightly sparse basket in May is a full one by July.
Given the choice, err on the low side. It costs less and finishes better - the basket range covers the sizes those numbers refer to.
Side planting changes everything
The reason a professional basket looks like a ball and a home one often looks like a bowl.
Planting through the sides of a wire or open basket fills the space between rim and base, which is where the volume comes from. Roughly a third of the total count should go in the sides, evenly spaced around, in one or two tiers.
A solid plastic basket cannot do this at all, which is why it needs a slightly different arrangement - the planting guide covers the technique.
The thriller, filler, spiller ratio
A useful way to divide the count rather than just hitting a number.
One centrepiece with height, in the middle.
A third of the remainder as filler, mounding plants that occupy the middle ground.
The rest as trailers, at the rim and in the sides - which for most baskets is the largest group.
Plug plants versus potted
Count the same way, but plugs need growing on somewhere frost-free for several weeks before they go in. Planting plugs straight into a basket in April usually disappoints.
Larger potted plants go in immediately and cost more. For one basket, buy potted; for six, buy plugs and grow them on.
All one variety, or mixed
Single-variety baskets are easier to get right - the plants grow at the same rate and nothing gets swamped.
Mixed baskets look better when they work and need matching vigour to do so. Pairing a vigorous trailer with a delicate one gives you a basket of the vigorous one by August - the flowers guide covers matching.
Compost volume is the real limit
What actually constrains the count is not surface area but how much compost each root ball has to draw on.
A deeper basket of the same diameter supports meaningfully more plants than a shallow one, which is why two 35cm baskets from different makers can want different numbers.
Watering rises with the count
Worth being honest about before buying twelve plants. More plants in the same compost means faster drying, which means more frequent watering in July.
If watering daily is not realistic, plant fewer rather than buying a drip system to support an overplanted basket - the care guide covers the routine.
Feeding rises too
A heavily planted basket exhausts its compost faster, so the six-week point when flowering drops off arrives sooner.
Slow-release granules at planting and a high-potash liquid feed weekly from six weeks is the standard - the compost and feed guide covers it.
Autumn and winter baskets
Use fewer. Autumn and winter plants are chosen for structure rather than mass and they will not knit together the way summer bedding does.
Three or five well-chosen plants in a 35cm basket is right for September - the autumn plants guide covers the season.
The liner decides how forgiving it is
A good liner with a moisture-retaining backing lets a basket carry more plants comfortably than an open one that dries in a morning.
Coco liners and the liners range cover them - and free UK delivery applies over £20.
The short version
- Five in a 30cm, seven in a 35cm, nine to twelve in a 40cm, including side planting.
- Eventual spread on the label matters far more than pot size.
- Overplanting looks magnificent in June and tired by August.
- About a third of the total count should go in the sides, not the top.
- More plants means faster drying - plant fewer if daily watering is not realistic.
Frequently asked questions
How many plants go in a 35cm hanging basket?
About seven, including side planting, as a working figure. Vigorous trailers need fewer and compact plants need more, so check the eventual spread on the label rather than going by pot size.
What happens if I overplant?
It looks magnificent in June and tired by August. Roots compete for a small volume of compost, the basket dries faster than you can keep up with, plants shade each other and flowering drops off.
How many plants should go in the sides?
Roughly a third of the total, evenly spaced in one or two tiers. Side planting is what fills the space between rim and base, and it is the difference between a ball of flowers and a bowl.
Should I use one variety or mix them?
Single-variety baskets are easier to get right because everything grows at the same rate. Mixed baskets look better when they work, but you need matching vigour or the strong plant swamps the others.
Do autumn baskets need the same number?
No, use fewer. Autumn and winter plants are chosen for structure rather than mass and will not knit together like summer bedding, so three or five in a 35cm basket is right for September.
