Best Plants for Rain Gardens

Plants for rain planters have to be able to tolerate some wetness at the root zone as well as grow in more normal conditions.

Typical plants include Iris pseudocorus and a range of perennials such as:

• Geraniums
• Persicarias
• Hemerocallis
• Grasses such as Deschampsia or Miscanthus

Some shrubs such as Cornus sanguinea or even trees, such as Betula would be suitable for a large planter. 

See the table below for a comprehensive list of plants suitable for rain gardens:

 

Common name	Scientific name	Habit	Sunlight and Aspect	Origin
Guelder rose	Viburnum opulus	Perennial shrub	Any	Native. Flowers attract insects and berries are eaten by birds.
Dogwood	Cornus sanguinea	Perennial shrub	Any	Native. Leaves are larval food for vase bearer moth and berries eaten by birds. Often planted for attractive winter stems.
Culvers root	Veronicastrum virginicum	Herbaceous perennial	Full sun or partial shade	Non-native. Tall with long terminal blue flower spikes. On the RHS ‘plants for pollinators’ list.
Aster	Aster spp.	Herbaceous perennial	Full sun or partial shade	Non-native. Often late flowering. Clump forming. Several species on the RHS ‘plants for pollinators’ list.
Black eyed susan	Rudbeckia birta	Herbaceous annual or biennial	Full sun or partial shade	Non-native. Spectacular yellow and black flowers. On RHS ‘plants for pollinators’ list.
Stinking hellebore	Helleborus foetidus	Herbaceous perennial	Full sun or partial shade	Native. Winter flowers.
Montbretia	Crocosmia spp.	Deciduous rhizomatous perennial	Partial shade	Naturalised. Red flowers. Thrives in most conditions.
Bugle	Ajuga reptans	Rhizomatous perennial	Partial shade	Native. Low growing and will form a mat.
Columbine	Aquilegia spp.	Herbaceous perennial	Full sun or partial shade	Non-native. Clump forming with tall flower spikes. On RHS ‘plants for pollinators’ list.
Inula	Inula hookeri	Herbaceous perennial	Partial shade	Tall clump forming with yellow flowers. On RHS ‘plants for pol- linators’ list.
Hemp agrimony	Eupatorium cannabinum	Herbaceous perennial	Full sun or partial shade	Native. Sub-shrubs with pink flowers.
Bellflower	Campanula glomerata	Herbaceous perennial	Full sun or partial shade	Native. Clumps bearing violet-blue bell shaped flowers.
Sneezeweed	Helenium sp.	Herbaceous perennial	Full sun	Non-native. Clump forming with red flowers. On RHS ‘plants for pollinators’ list.
Lesser periwinkle	Vinca minor	Perennial sub-shrub	Any	Non-native. Ground cover with blue flowers.
Elephants ear	Bergenia sp.	Rhizomatous perennial	Full sun or partial shade	Non-native. Large leaves and pink flowers.
Plantain lilies	Hosta spp.	Herbaceous perennial	Part shade	Non-native. Attractive light coloured flowers.
Yellow flag	Iris pseudocorus	Rhizomatous perennial	Full sun or partial shade	Native. Likely to prefer wetter areas near inlet.
Siberian flag	Iris sibirica	Rhizomatous perennial	Full sun or partial shade	Non-native. Blue flowers. Prefers moist but well drained soil.
Garlic and onions	Allium spp.	Bulbous perennials	Full sun	Non-native. On RHS ‘plants for pollinators’ list.
Soft rush	Juncus effusus	Evergreen perennial	Full sun or partial shade	Native. Form tussocks – likely to prefer wetter areas.
Pendulous sedge	Carex pendula	Rhizomatous perennial	Full sun or partial shade	Native. Nodding flower spikes. Likely to prefer wetter areas near inlet.
Zebra grass	Miscanthis sinensis	Perennial, deciduous grass	Full sun	Non-native. Tussock forming ornamental grass with silky flowers.
Switch grass	Panicum virgatum	Deciduous perennial grass	Full sun	Non-native. Tussock forming ornamental grass.
Royal fern	Osmunda regalis	Deciduous fern	Any	Native. Large clump-forming plants.
Male fern	Dryopteris felix-mas	Deciduous or evergreen fern	Partial shade or full shade	Native. Large shuttlecock-like form.
Broad buckler fern	Dryopteris dilatata	Deciduous or evergreen fern	Partial shade or full shade	Native. Large shuttlecock-like form.

 

 

(From Thames Water UK Rain Garden-Guide)

Rain Garden Planters: An Attractive Adaptation of Sustainable Drainage Systems (SuDS)

 

 

Designed for Flooding

Even if you don’t have room for a rain garden you can still implement sustainable stormwater management. Rain garden planters, or gutter planters, handle rainwater runoff from rooftops and operate like a rain garden inside a planter.

Rain garden planters are perfectly suited to small spaces, as they can be built close to buildings in any configuration and don’t take up very much space.

These planters are an attractive adaptation of Sustainable Drainage Systems (SuDS) which slows surface water flows,
and reduces surface water flood risk.

With both bioretention and additional internal storage, these planters are an innovative solution to property level retro-fit SuDS, and can work out very much less expensive than most groundworks interventions.

The planter can be made from a number of materials, but we prefer commercial quality Larch Planters for the following reasons:

• produced by UK craftsmen using Larch from sustainably grown larch woodlands.
• Larch produces its own intrinsic preservative providing a very long planter life without the use of toxic preservatives.
• Alternative materials are linked to non sustainable production issues from energy consumption to pollution or toxic issues.

A rain garden planter is a waterproof container filled with layers of:

• mulch
• soil
• sand

These layers filter the water before it passes to the next stage of rainwater management.

Water may discharge from a planter into the normal drains or it could be diverted further into a Rain Garden.

For an enhanced biophilic and aesthetic effect, we like to encourage the construction of landscaped features that the water could travel along and slowly percolate into the soil, such as an attractively constructed rill, gulley or channel into a garden bed, as in the example below.
   

 

 

 

SuDS Planter Storage and Flow Rates

 

The storage volume and retention and subsequent outflow rates will vary with the dimension of the planter to be incorporated into the scheme. East of Eden SuDS planters are all based on the internal design features as recommended bySouth East Rivers Trust, which was founded on extensive trial studies (See tables 2-4* below).

The SuDS Manual states that typically the surface area of a bioretention feature would be 2-4% of theoverall site area being drained, to prevent rapid clogging of the bioretention surface. Based on thisguidance, the surface area of any planter (or combination of planters) should not be less than 2-4%of the roof area it is draining. Where possible, the size of the planter should reflect this recommendation.
 

As such, we offer a range of standards planter sizes to use in

1000mm L x 650mmW x 900mm H to 2000mm L x 650mm W x 900mm H
 

These sizes are based on large, but manageable and movablesized units using a fork lift. This offers practical sized units option to be used in combination to achieve the recommendation catchment areas stated above.
 

If the site permits, we can also construct the SuDSplanter to bespoke requirements up to a maximum of:
 

       3000mm Lx 1000mm W x 950mm H
 

 

Storage Layer

As mentionedthe storage value will depend on the dimensions of the planters.
 

Based on a planter with the dimension of 3000 x 1000W x 750Htrials have provided the storage and outflow rates as in Tables 1 & 2

With a minimum planting layer of 450 mm and further 50 mmgap to the top of the planter, this would leave approximately 300 mm for a sub-base / storage layer.
 

Using geocellular crates in the planters a greater volume of storage can beachieved. Typically 250 mm depth of geocellular crates are used

 

Tables 1 and 2 compares the storage values ofthe standard Gravel sub-base SuDS planter with the Geocellular Sub-BaseSuDSplanter  -
 

Table2*.Dimensions and storage volume –GravelSub-BasePlanter.

 

Features	Length (m)	Width (m)	Depth (m)	VoidSpace (%)	Storage Volume(m3)
Gravelsub-base	3	1	0.3	30 approx.	0.27
Planting Medium(soil)	3	1	0.35	20 approx.	0.21
Planter Surface to OverflowPipe Level	3	1	0.05	100	0.15
Total Available      Storage					0.63 (630 litres)

Table3*.Dimensions and storage volume –GeocellularSub-BasePlanter.
 

 

Features	Length (m)	Width (m)	Depth (m)	VoidSpace (%)	Storage Volume(m3)
Geocellularsub-base	3	1	0.25	95	0.71
Planting Medium(soil)	3	1	0.4	20(highlevel estimate)	0.24
Planter Surface to Overflow Pipe Level	3	1	0.05	100	0.15
Total Available Storage					1.10
					(1110 litres)

 

Outflow rates

The standard SuDS planters are drained via a perforated drainage pipe running along the bottom of the planter. A number of factors influence the drainage rate including the drainage pipe diameter,soil mix and therefore infiltration rate,impact of plants and soil conditions prior to any particular rainfall event will be important.

Table 3 shows outflow rates from trials showing the effect of the outflow diameter on the outflow rate.
 

Table 4*. Estimated maximum flow rate for a 68 mm downpipe, with water distributed into planter via a pipe set at approximately 1 in 200slope.

 

 

Diameter of outflowmm)	Estimated maximum flowrate (litrespersecond)	Estimated maximum flowrate(cubicmetres persecond)	Estimated maximum flowrate (litresperhour)	Estimated maximum flow rate (cubicmetres perhour)
30	0.21	<0.001	752	0.75
40	0.46	<0.001	1648	1.65
50	0.84	<0.001	3020	3.00

* Based on data from South EastRivers Trust
 

Based on trial data, the narrower diameter is recommended to limit the flow out of the  planter to a reasonable level to maximise the potential for flood storage, especially where extra storage was provided by the geocellular storage. One hour after a rainfall event begins, up to 0.75m³of water can drain from the bottom of the planter.

Depending on the choice of storage layer,an additional 0.62-1.1m³of water can be stored in the planter before it over flows.This means that over an hour following the beginning of a rainfall event, between 1.37 m³ and 1.85 m³ can enter the planter before water drains via the over flowpipe.

 

In reality the infiltration rate of the soil will have a notable impact of the volume and rate of water which can drain out of the bottom of the planter. Hence the taller the planter  the slower the infiltration rate. Also, the larger the overall dimensions of the planter will allow for more storage before the water level reaches the overflow.