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[[File:Sizing flow-through planter.jpg|thumb|A flow-through planter comprises a ponding zone, mulch layer, filter media for planting, and a supporting gravel drainage layer]]
[[File:Sizing flow-through planter.jpg|thumb|A flow-through planter comprises a ponding zone, mulch layer, filter media for planting, and a supporting gravel drainage layer]]
This article is specific to flow-through [[Stormwater planters|stormwater planters]], vegetated systems that do not infiltrate water to the native soil. <br>
If you are designing a planted system which does infiltrate water, see advice on [[Bioretention: Sizing]].
The dimensions of a stormwater planter are largely predetermined according to the function of the component. As they do not contain a storage reservoir the planters rely more upon careful selection of materials. Both the saturated hydraulic conductivity of the filter media and the number and size of perforations of the [[underdrain]] pipe play critical roles for flow control. Options for maintaining separation between filter media and clear stone aggregate surrounding the perforated pipe include a 100 mm deep choker layer or sheet of geotextile filter fabric.
{| class="wikitable"
|-
! Component
! Recommended depth (with underdrain pipe)
! Typical porosity (''n'')
|-
| Ponding (''d<sub>p</sub>'')
| 150 to 450 mm
| 1
|-
| [[Mulch]]
| 75 ± 25 mm
|
* 0.7 for wood based
* 0.4 for stone
|-
| [[Bioretention: Filter media|Filter media]] (''d<sub>m</sub>'')
|
* 300 mm to support turf grass (and accept only rainwater/roof runoff)
* 600 mm to support shrubs, flowering [[perennials]] and decorative [[grasses]]
* 1000 mm to support [[trees]]
|
* 0.4 for sandier Blend A - Drainage rate priority;
* 0.35 for more loamy Blend B - Water quality treatment priority
|-
| Choker layer
| 100 mm
| 0.4
|-
| Perforated pipe diameter
| 150 to 200 mm
| 0.4
|-
| Clear stone aggregate layer below perforated pipe
| 50 mm (although commonly omitted altogether).
| 0.4
|}