Plant Spacing Calculator

How Plant Spacing Works

This free plant spacing calculator works out exactly how many plants you need to fill a bed, border or hedge run. Enter your dimensions, pick a planting pattern and the spacing between plants, and you get instant results for total plant count, plants per square metre, and roughly what the job will cost. It is the same maths you would do on a clipboard at the garden centre, but without the arithmetic mistakes that end up costing you an extra trip.

There are three patterns gardeners actually use, and each suits a different job. Grid places plants in straight rows and columns, which is how almost every vegetable plot and formal bed is set out. Triangular (sometimes called offset, staggered or hexagonal) shifts every second row sideways by half the spacing, so each plant sits in the gap of the row in front of it — this pattern is commonly used for ground cover, dense planting and anywhere you want a solid canopy. Row is what you use when you are planting a hedge, a row of leeks or onions, or doing traditional drill-sown vegetables. Each pattern uses slightly different maths, and picking the right one changes how many plants you buy.

The calculator converts all your inputs into metric internally, so you can mix units without doing the conversions yourself. Bed length in feet, spacing in centimetres, no problem. If you want the live UK-climate sowing dates that go with this, our planting calendar covers 30+ vegetables month by month. For raised bed dimensions, pair this with the raised bed calculator and the compost calculator to work out the fill at the same time.

UK Plant Spacing Reference Table

Every plant has a recommended spacing based on its mature size, its feeding needs and the effect you want in the bed. The spacings below are on the generous side rather than packed in tight, which reduces disease and gives each plant room to fill out properly. For smaller gardens or cottage-garden effects, reduce spacing by 20-25% (our own rule of thumb, not an RHS figure). For formal borders or nutrient-hungry crops, stick to these exactly.

As a quick rule of thumb, anything taller than it is wide (delphinium, hollyhock, verbena bonariensis) gets 45-60cm spacing. Anything that spreads more than it grows tall (geranium, thyme, alchemilla) gets 30-40cm. Shrubs go at 60-120cm depending on eventual size. For mixed borders, stagger the heights from back to front and let the spacings overlap visually — if two neighbouring plants of the same size are at 45cm, they will knit by the end of the second season and look like a proper drift rather than dots on a grid.

Why Triangular Spacing Fits 15% More Plants

The 15.5% figure is not marketing — it comes straight out of geometry. In a grid pattern, each plant sits in the centre of a square footprint with a side length equal to the plant spacing. For 30cm spacing, each plant “owns” a 30cm x 30cm = 900 cm² area, which works out at 1 / 0.09 = 11.1 plants per square metre.

In a triangular (offset) pattern, each plant sits in the centre of a hexagonal footprint instead. The hexagon has the same edge-to-edge distance as the grid’s square (the plant spacing stays the same between neighbours), but the area of a regular hexagon with that same edge-to-edge distance is s² x √3/2, or roughly 0.866 x s². For 30cm spacing that is 0.866 x 900 = 779 cm² per plant, which works out at 1 / 0.0779 = 12.8 plants per square metre — 15.5% more than the grid.

In practical terms, if you are planting a 10 m² bed with perennials at 40cm spacing, the grid pattern needs 62 plants and triangular needs 72 plants. The extra 10 plants cost you perhaps £35 but you get full canopy cover a season earlier, weeds are suppressed faster, and you avoid the straight-line gaps that grid planting leaves between the rows. For any ground cover or dense planting project, triangular is almost always worth the extra plants. For vegetables where you need to hoe between rows, stick with grid.

The maths in the calculator uses the formula: total plants = (length x width) / (spacing² x 0.866). It rounds down to a whole number because you cannot buy fractional plants, and in practice the edges of the bed mean you lose 1-3 plants to the margins in any real-world layout. If you are ordering for a professional job, budget 5-10% extra to cover breakages and replacements.

Hedge Spacing Rules of Thumb

Hedge spacing depends on two things: the species and its final size, and whether you are planting a single row or a double staggered row. The RHS gives hedge planting distances of 30-60cm, depending on the plants’ final size, the size of hedge required and plant vigour, and suggests a staggered double row only for hedges thicker than 90cm. Its hedge selection guide puts a few vigorous species wider than that, such as Leyland cypress at 60-75cm.¹³

Single Row Hedges

For a single-row hedge, the spacing depends on the species. The RHS suggests about 30-40cm for common box (Buxus sempervirens), with compact cultivars at 10-15cm.²

The RHS hedge selection guide gives these spacings for average conditions: lavender 30-37.5cm, common privet 37.5cm, hornbeam 45cm, holly 45-50cm, beech and yew 45-60cm, cherry laurel and Portuguese laurel 60cm, and Leyland cypress 60-75cm.¹⁴

A 10m hedge of beech at 45cm spacing needs (10 / 0.45) + 1 = 23 plants; at 60cm, the top of the RHS range for beech,¹⁵ the same 10m needs (10 / 0.6) + 1 = 17 plants, rounded down.

Double Staggered Row Hedges

For hedges thicker than 90cm, the RHS suggests a staggered double row: two rows 45cm apart, with plants 90cm apart within each row, offset so the two rows form a zig-zag.¹³ A 10m run at 90cm spacing needs (10 / 0.9) + 1 = 12 plants in the first row, rounded down. The second row starts 45cm in to make the zig-zag, so only 11 fit before the 10m end: 23 plants in total.

When to Plant Hedges

The RHS advises planting deciduous hedges from mid-autumn to late winter, and evergreen and semi-evergreen hedges such as box, privet and yew ideally in early autumn, although they can go in at any time from late autumn until late winter. Bare-root hedging is only available in winter and early spring, while the plants are dormant. Delay planting if the soil is waterlogged or frozen, and keep a new hedge well watered for its first two years.¹³ For specific sowing and planting dates for your region, see our UK planting calendar.

Common Spacing Mistakes

Each of these costs you time, money or both, and all four are easy to avoid once you know about them.

1. Overcrowding

The most common mistake by far. A 10cm-wide plant in a 9cm pot at the garden centre looks tiny, and it is tempting to plant four where you should plant one. Three years later that 10cm plant is 1m across and has smothered its neighbours. Always plant at the spacing recommended for the mature size of the plant, not its current size. If the bed looks sparse in year one, fill the gaps with annuals like calendula, cosmos or nasturtium for the first two seasons. By year three the permanent plants will have filled out and the annuals can stop.

2. Ignoring Mature Size

Plant labels always give the mature spread, usually after 5-10 years. A 50cm x 50cm label means the plant will occupy a 50cm circle when mature — it needs 50cm clear space around it. If you plant two 50cm spreaders 30cm apart because “they look small now”, one of them will have to come out within 3-4 years. For any permanent planting (shrubs, perennials, trees), trust the label even if it looks wasteful at first.

3. Mismatched Microclimates

Even spacing does not help if plants are in the wrong position. Plants in full sun need more space than plants in partial shade because they grow more vigorously. A lavender in full sun at 40cm spacing will fill its allotted space within two seasons; the same lavender in partial shade may never reach 40cm spread and will look gappy. Before finalising spacing, check which side of the bed gets morning vs afternoon sun, and, as a GardenCalc rule of thumb, plan for 10-15% tighter spacing on the shaded side.

4. Forgetting Access

If you cannot reach the back of your bed without stepping on plants, you will not weed it, deadhead it or harvest it. The RHS says beds of around 1.2m width should let you reach the centre from either side, and suggests planks to spread your weight where beds are wider; paths about 45cm wide between beds help with access.¹⁶ By the same logic, a bed you can only reach from one side works best at about half that width, around 60cm. For vegetable beds, make sure every row of plants is within arm’s reach of a path. Access paths are not wasted space — they are the difference between a bed you maintain and a bed you ignore.

Container and Pot Spacing

Container planting uses a different rule from bed planting. Because each pot is a closed system with finite compost, the spacing inside a pot matters less than the ratio of plants to pot volume. The industry rule for mixed containers is called “thriller, filler, spiller” — one tall centrepiece (the thriller), three to five mid-height filler plants and two or three trailing spillers around the edge.

The Three Rule of Thumb

For pots up to 30cm (12 inch) diameter, plant in groups of three: one thriller, two spillers, or one thriller with two fillers tucked around it. For pots 30-45cm (12-18 inch), plant groups of five: one thriller, three fillers, one spiller. For pots over 45cm (18 inch), plant groups of seven or more, arranged in a rough triangle with the thriller off-centre and fillers stepping down in height towards the spiller at the front.

Spacing Inside the Pot

Plants in a container can go tighter than bed spacing because they will be watered and fed more intensively and will rarely reach their mature size in a single season. Halve the bed spacing for summer bedding in pots — if a petunia is 20cm apart in the ground, put them 10cm apart in a pot. For permanent container plants (box, acer, hydrangea), use the normal spacing but pick one focal plant and let it fill the pot alone rather than cramming three in. A 45cm pot with one well-grown hosta or hydrangea looks far better than three plants fighting for compost.

Working Out Compost Volume

Once you know how many pots you need, use our compost calculator to work out how much peat-free compost to order. As a rough GardenCalc estimate, not a manufacturer figure, a 30cm pot needs about 20 litres, a 45cm pot needs 55 litres, and a 60cm pot needs 130 litres. Pot shapes vary, so check the litres on the pot or the compost bag. For long-term container planting, mix the compost 60:40 with topsoil from the soil calculator to reduce settling and add weight for stability. Feed every two weeks with a liquid fertiliser through the growing season.

Frequently Asked Questions