Trees
Tree Sizes & Specifications
How we measure and specify our trees
Trees are measured and specified in a few standard ways, depending on their form. This guide explains the terms you will see on our availability lists, quotes and in the industry, so you can choose and specify with confidence. If you are not sure what you need, our team is always happy to help.
On this page: girth sizes · clear stem and height · multi-stem trees · pleached, parasol and topiary · hedging · root types · writing a specification
Girth sizes for standard trees
Standard trees, with a single clear trunk, are sized and priced by girth: the circumference of the stem in centimetres, measured 1 metre above ground level. As a tree grows, its girth increases, along with its height, spread and root ball.
| Girth (cm) | Common description | Typical height |
|---|---|---|
| 6–8 | Light standard | 2.5–3 m |
| 8–10 | Standard | 2.5–3 m |
| 10–12 | Selected standard | 3–3.5 m |
| 12–14 | Heavy standard | 3.5–4.25 m |
| 14–16 | Extra heavy standard | 4.25–5 m |
| 16–18 and 18–20 | Extra heavy standard | 4.5–6 m |
| 20–25 and above | Semi-mature | 5 m and above |
Heights are a guide only and vary by species: an upright hornbeam and a weeping cherry of the same girth look very different. Semi-mature and specimen trees can go well beyond 40 cm girth; ask us about larger sizes.
Clear stem and overall height
Clear stem is the height of trunk from the ground to the lowest branch. Standards usually have 1.8–2 m of clear stem; half standards around 1.2–1.5 m.
Overall height is measured from ground level to the top of the tree, usually given as a range in centimetres, for example 300–350 cm.
Feathered trees keep their side branches almost to the ground and are specified by height.
Transplanted (for example 3xTr) tells you how many times a field-grown tree has been lifted and replanted on the nursery. Each move encourages a more compact, fibrous root system that establishes better.
Multi-stem trees
Multi-stem trees grow with several stems from the base, so girth is not used. They are specified by overall height, for example 250–300 cm or 400–450 cm, with the number of stems and, for larger trees, the spread. Every multi-stem is individual, which is why we encourage you to choose yours in person.
Pleached, parasol and topiary
Pleached trees: clear stem height, frame size (for example 120 × 120 cm or 150 × 150 cm) and girth.
Parasol trees: clear stem height and canopy frame size.
Topiary: the dimensions of the shape, such as ball diameter or cone height, and the pot or root ball size.
Hedging
Hedging is specified by height in centimetres and, for instant hedging, by width and length. Instant hedging is usually supplied in pre-formed sections, often 1 metre long, so you can plan a hedge by the metre. Younger hedging plants are supplied by height and planted at a set number per metre, typically 3 to 5 depending on size and species.
Root types
| Code | Root type | Planting season |
|---|---|---|
| RB / WRB | Root-balled: field-grown, lifted with soil in hessian, often in a wire basket | Late autumn to early spring |
| BR | Bare-root: field-grown, lifted with no soil | Late autumn to early spring |
| C + litres (e.g. C35, C250) | Container-grown in a pot of that volume | All year |
| Air-Pot | Grown in an air-pruning container for a dense, fibrous root system | All year |
Root-balled trees offer the best value; container-grown trees can be planted at any time of year. Both are peat-free at Form. Read field-grown or container-grown trees: which is right for you?
Writing a tree specification
A clear specification helps us quote accurately and makes sure you get exactly what you expect. A typical line includes:
Botanical name, including cultivar, for example Tilia cordata 'Greenspire'
Form: standard, multi-stem, feathered, pleached, parasol
Size: girth for standards, height for multi-stems and feathered trees
Clear stem, where relevant
Root type: RB, BR, container size or Air-Pot
Quantity, and whether trees need to be matched
Examples:
Tilia cordata 'Greenspire', standard, 16–18 cm girth, 2 m clear stem, RB, 6 matched
Amelanchier lamarckii, multi-stem, 300–350 cm, 4–5 stems, C250, 1
Frequently asked questions
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Girth is the circumference of the stem, measured in centimetres at 1 metre above ground level. Standard trees are sold and priced by girth band, for example 12–14 cm.
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The clear stem is the height of the trunk from ground level to the lowest branch. Most standard trees have a clear stem of around 1.8 to 2 m, so you can walk beneath the canopy.
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Multi-stem trees are specified by overall height, for example 250–300 cm, rather than girth, along with the number of stems and, for larger specimens, the spread.
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RB means root-balled: field-grown and lifted with a ball of soil wrapped in hessian and wire, available in the dormant season. C followed by a number, such as C35, means grown in a container of that many litres. Air-Pot trees are grown in specially designed containers that encourage a dense, fibrous root system. Container and Air-Pot trees can be planted all year.
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Yes. Send us your schedule or describe what you are looking for, and our team will help you specify sizes, forms and root types that can be sourced for your timescale.
Need help with a specification?
Send us your schedule or tell us what you are looking for. We will help you specify sizes, forms and root types that can be sourced for your timescale, and quote for the whole list. Email info@formplants.com.