Catch It, Slow It, Use It, Lose It – Rain Planters

Rain planters are a brilliant and versatile solution for managing rainwater in your garden, especially if you’re working with a small or urban space.

In their simplest form, they don’t necessarily capture water for long-term storage like water butts or dipping tanks as the planting material absorbs and holds it for use by the planting and slow release back to the drain or garden.
However, quite simply, rain planters shine in every other area of sustainable rainwater management!

They help to catch rainwater and slow it down, clean it via infiltration, and can then release it slowly into the surrounding ground or, back into the drain, making them a perfect choice for managing excess water while enhancing your garden’s beauty and biodiversity.

However, it is possible to buy (or construct) versions of these multifunctional planters that also include a tank for storage once the water has passed through the surface of the planter (or directly into the tank) allowing you to enjoy all the benefits of sustainable rain management there are!

The principle functions of a Rain Planter:

1. Catch It
Like the features we’ve looked at previously, rain planters are constructed to catch rainwater run off from gutters and downpipes.
The water is channelled into the planter which manages the flow, even in heavy downpours, to help prevent excessive run off onto surfaces or into the drain, reducing the pressure on local drainage systems.

2. Slow It
One of the key benefits of rain planters is that they help to slow the flow of rainwater. What’s contained within the planter allows the water to infiltrate and percolate slowly towards the base of the container where the excess finds its way into the overflow pipe.
This feature of rain planters is particularly important in urban areas where traditional drainage systems often struggle to cope with heavy rainfall and become overwhelmed.
By slowing down the release of water, rain planters can help reduce the risk of surface flooding and contribute to more balanced drainage systems.

3. Clean It
As rainwater flows down through the planter, it is naturally filtered through the soil/compost, aggregate and plants. This process helps to remove pollutants, debris, and chemicals that may have been washed off roofs (or pavements, or roads in the case of urban locations).
The soil acts as a natural filter, improving the quality of the water before it is released back into the drain or, soaks into the ground. This can help prevent polluted run-off from reaching local rivers and streams, protecting water quality and local ecosystems.

4. Use It
Unless they have specifically been built to do so, most rain planters don't typically store water that’s useable elsewhere - they allow for immediate use of the captured rainwater by the plants within them and retain moisture within the planter itself for a prolonged period afterwards.
This inherent store of water contained within the gaps between aggregate and soil in the planter can promoting continuing healthy growth and keep your garden space green and vibrant, even through drier periods where a traditional plant pot would be reliant on regular watering.

In addition, rain planters are often designed with plants capable of tolerating both periods of drought and short bursts of water logging in mind (as well as any other environmental factors specific to the site) so, it really can be one of the lowest maintenance types of planting you can install!
The ‘right plant, right place’ approach to selecting planting is important for not just Rain Planters but, for anyone looking to create a sustainable and self-sufficient planting space.

5. Lose It – Release It Slowly (or, store it!)
After your rainwater has been filtered and some of it has been a) absorbed by the plants b) evaporated from the surface of the soil or the plants themselves (called evapo-transpiration) it’s slowly released back into either the surrounding soil or the drainage system.

If going back into the ground, this slow release helps to recharge groundwater levels or, the reduced rate and volume of run off going into the drain helps reduce the strain on local drainage systems.

If you're adding storage for future use to your list of benefits, a simple tap arrangement at a convenient height will allow you to access your water.

6. Additional Planting Space for People and Wildlife
Rain planters have the additional bonus of creating additional planting space!
Even (and, especially) in small or urban spaces, you can incorporate rain planters to add greenery, flowers, or even introduce edible plants to your garden.

The plants in the planters are not only good to look at, they also attract beneficial insects, pollinators like bees and butterflies, and even birds, helping support local wildlife.

For gardeners, rain planters provide an opportunity to increase the biodiversity of their spaces – potentially introducing new plant species, create seasonal interest, and experiment with different styles of planting by the different planting conditions they can present.

7 Accessible to all
As Rain Planters are effectively raised planting beds, they’re particularly useful for those who want to grow plants in garden (or yard) areas that might otherwise be too dry or too compact to plant directly in the ground or, if you have no soil in your space.
As they are raised up and can be adapted to any height as required, they can form an integral part of accessible gardening, and can be particularly useful in schools and community settings. Here they also present opportunities for learning and teachable moments across a range of curriculum subjects.

A Beautiful, Practical, and Sustainable Solution
Rain planters are an ideal option for anyone looking to incorporate sustainable rainwater management into their garden without taking up much space. They don’t have to require a large investment or complicated installation, and they fit perfectly in urban settings, smaller gardens or courtyards.

Not only do they help catch, slow, clean, and release rainwater, but they also contribute to the beauty and biodiversity of your space. Whether you’re a homeowner, a community group, or someone working in a school garden, rain planters are an easy, low-maintenance way to make a real difference in how you manage rainwater bringing with them lots of other benefits.

Constructing Rain Planters:

Kit list:

• Your planter of choice (50cm x 50cm x 50cm is around the minimum volume you would want to use depending on your expected flow of rainwater to it)
• Pipework – 40mm pipes, 1 right angled elbow joint, leaf guard (or other – see below) connection to outlet (see below)
• Non woven horticultural fleece / geo textile
• 10mm size aggregate: gravel, stone chips – washed and free of sand/sediment
• Peat free compost
• Your choice of plants subject to site conditions
• Stone/pebbles 20mm+ for surface mulch

You will need to calculate the amounts of aggregates, compost, fleece and plants based on the size of the planter and the approximate depths required.

Choosing your location:
You need access to a down pipe. It doesn’t have to be directly next to where you want your planter to sit however, if it's not directly next to it, you'll need to consider how you’re going to get your water to the planter.

This can present a challenge but, also an opportunity to get creative!: Pipework, guttering, rain chains or, however you choose to convey it there. You can pipe it in discreetly or make it part of the feature.

Pintrest has lots of inspiration for ways to make a feature of your waters route to the planter - all it takes is a bit of imagination!

Of course, it’s also possible to position the planter so that the downpipe releases water directly into the planter via a diverter attached to it or, by redirection of the existing guttering.
Either way, as the water reaches the surface of the planting and compost it’s important to break its fall so it doesn’t damage the planting or dislodge the compost which we’ll look at later.

In terms of location, you will also need to consider where the overflow outlet will direct the excess water from the planter to. Is there a drain associated with the downpipe that could be used or, is it possible to allow it to run out and onto a patio or planted area which allows it to drain away safely?

Choosing the Right Container:
You’ll need a large, sturdy container. It needs to be strong enough to contain both gravel aggregate for drainage, the necessary pipework, compost and planting as well as the water that will fill up the remaining space between it all.
It also needs to be water proof internally and if it doesn’t come with one already, it will also need to have a hole drilled into it to allow the overflow pipe to exit.

A sturdily built-for-purpose wooden planter or a pre-made metal planter or trough can work well with the former needing to be lined to ensure it’s waterproof.

Depending on your roof area catchment, 50Cm x 50cm x 50cm is about the smallest you would really want to make a rain planter to be able to catch and slow a meaningful amount of water and fit some planting in.

Make sure your planter is in position before you start filling it. If it’s heavy to start with it’s only going to get heavier!

Pipework:
You’ll be creating a ‘French drain’ type arrangement in the bottom of the planter with an upstanding overflow pipe to the surface of the planter. Something like 40mm plumbing pipe works well. You'll also need a right angled elbow joint and any guttering or pipework to get your water from your roof to the planter in the first place.

Depending on how your planter and its location, you'll also need to consider how the overflow leaves the planter. Will it:

• Leave the planter in a pipe directed towards an existing drain?
• Flow out the hole in the planter to the patio, planting bed or towards a drain?

Consider if you need another connection between the inside and outside of the planter and/or a narrower pipe to the outside to get the water where you want it to go.

Cut the pipe to fit to the bottom of your planter and meet the exit hole and also a section for the upright. The vertical length of pipe needs to sit about 20mm below the top of the planter and approx 40mm above the top of the compost when filled.

Attach the pipes using the right angled elbow join and ensure it fits into the planter.

Drill 5-6mm holes along the top half of the horizontal pipe in a zig zag pattern - as the planter fills with water, this will allow the excess to seep into the pipe and out of the overflow (this is known as a French Drain system).

You’ll want a leaf guard to fit over the top of the overflow pipe to stop leaves or debris going in.

Fit anything that is required to the outside of your planter to direct the overflow water away and ensure the pipes inside are gently angled to fall towards the outlet.
Once you’re comfortable the internal pipework is securely connected you can begin to fill the planter.
(I prefer to seal around the hole for the overflow after the aggregate is filled in around the pipework to stabilise it).

Filling the Planter:
Adding a Gravel Layer: To ensure proper drainage, you need to add a layer of gravel to the bottom of the planter, approximately 50mm deep. Put a bit of gravel in to rest the pipework on initially –remember, it should be sloping very gently towards where it is attached to the outlet hole.

At this point, use the waterproof sealant around the inside of the exit hole if you’re going to.

Backfill around the pipe to the required depth (the pipe should be fully covered). This should hold it more securely in place.

Use the sealant on the outside of the exit hole if required and test the water through flow from both the holes in the horizontal pipe and the top of the vertical pipe. If you’re happy, proceed:

Cover the top of the gravel with the geotextile to prevent compost from getting washed down through the gravel and into the drain. Cut the geotextile to fit neatly around the vertical pipe.

Then add your peat free compost to the level you are looking to plant to. You should aim for a minimum of 300mm/30cm depth of compost in your planter.
Remember to allow the material to settle a bit before planting as the level may drop considerably as it first becomes saturated.
(Alternatively, you can compress it very gently but, be careful - you don’t want to squash all the air pockets out of it as this is where the rainwater will be stored!)

Then, you can add your plants...

Planting:
It’s good to think about your planting as a community, working together to help create structure in your planters soil/compost and draw up lots of water as it becomes available.

To achieve this is the most efficient way, a good mix of different types of root system is useful. For example, mixing shallow, fibrous grass roots along with with deeper ones.

You also need to consider the light conditions and aspect of the planter – it is predominantly in shade or, does it sit in full sun?
This will help you work out what plants will be best suited to the job.
Do you want year round structure (likely, yes!) Bear this in mind when selecting plants and ensure a mix of evergreen and semi evergreen plants rather than herbaceous ones that will die back in Winter.

When looking for plants for your own specific space, you may wish to consider those that will tolerate seasonal dry and wet conditions such as those suggested by the RHS: https://www.rhs.org.uk/plants/for-places/wet-dry-soils

I've included a few plants below for you might consider using however, there are many more that will tolerate the periodic flooding / dry cycle..

Heuchera (evergreen or semi evergreen varieties)
Carex grasses (various)
Iris psuedacorus
Vinca minor
Persicaria bistorta
Luzula nivea
Astilbe (various)
Hardy ferns such as Dryopteris and Polystichum

The above are smaller plants some of them, herbaceous. If your rain planter is very large, you might want to include a structural element such as a multi-stem shrub or small tree, that is suited to the conditions such as Sambucus or Cornus.
Experiment with plants that give you something to look at all year round (and stay away from seasonal bedding plants!)

Tidying and testing:
You’ll need to add some sort of a filter or leaf guard to the top of the upstanding overflow pipe. This is to prevent debris, like leaves, twigs and compost from entering the planter and clogging the drainage system.

You can usually buy plastic leaf guards or, if the top of the overflow is going to be concealed amongst the planting, a piece of thin cloth can be held with an elastic band over the end as long as it does the job.

Mulch around the planting with some larger pebbles or stones to break the fall of the water entering the planter paying particular attention to any areas where there is direct water fall impact on the surface of the compost.

Again, you can test the overflow pipe to ensure nothing has shifted in filling the planter and, if you can, test the inflow from your down pipe, rain chain or other inlet using a watering can.

You’ll want to keep an eye on the planter as it experiences its first heavy rainfall to ensure it behaves as you would expect it to.

Some expected / normal observations:

• Depending on the size of your planter and the rate of rain fall, you may need to wait some time before you see anything coming out of the overflow hole / pipe.
• Unless the overflow is relieving excessive surface flooding at the top of the planter, any water leaving the planter should be coming out at a much reduced rate and volume.
• In very heavy rain, periods of surface flooding are normal and will drain away through the compost and gravel within a few hours.
• If your plants are treated to a deluge of rain water soon after planting, they may look a bit bedraggled. Don’t worry, they will bounce back and, once established, look a lot less affected by being inundated with water.
  

Check on the planters performance periodically and that the plants appear to be thriving in their conditions.