Guest post by Phoebe Webster, our Nature Recovery Ranger at North Bristol NHS Trust

What is drought-tolerant planting?

Drought-tolerant plants thrive in dry, free-draining soil with minimal rainfall. These plants range from hardy cacti to luscious, green, flowering varieties. Many of the drought-tolerant species that we use in the UK evolved in dry Mediterranean regions. Often confused with drought-resistant plants (which can withstand very long periods of time without watering), drought-tolerant plants will still require watering during very dry spells, but much less than other species.

Why create a drought-tolerant bed?

As climate change accelerates, it will test the ability of plants and animals to adapt to their changing environment. This makes it particularly important to provide plants that will be able to withstand the drier, hotter summers that it is known climate change will bring. This will allow the plants to not only withstand the natural stresses that they face, but to thrive. Drought-tolerant plants ensure continued habitat and food sources for the wildlife on site.

Drought-tolerant plants are typically low maintenance, which can take the pressure off estates, grounds staff and gardening groups to keep on top of watering and weeding. Beds planted for dry conditions are also useful in areas where easy access to water is not available or where plants need to be put into raised beds and not directly into the ground. Maintaining ornamental beds can be a strain, but drought-tolerant planting can give you a flourishing border with maintenance schedule that is easier to manage.

Examples of drought-tolerant planting

Drought-tolerant border planting plan at North Bristol NHS Trust
Drought-tolerant border planting plan at North Bristol NHS Trust
The border at Southmead Hospital before planting
The border at Southmead Hospital before planting. Photo: Phoebe Webster / Centre for Sustainable Healthcare 2021. Attribution 4.0 International (CC BY 4.0).
The drought-tolerant bed in place, in time for summer
The drought-tolerant bed in place, in time for summer. Photo: Phoebe Webster / Centre for Sustainable Healthcare 2021. Attribution 4.0 International (CC BY 4.0).
Flowers in the new drought-tolerant bed
Flowers in the new drought-tolerant bed. Photo: Phoebe Webster / Centre for Sustainable Healthcare 2021. Attribution 4.0 International (CC BY 4.0).
Southmead Hospital’s ICU roof terrace:

When thinking about planting on the ICU roof terrace we needed to develop a relatively low-pressure maintenance plan.

The biggest issue we had to tackle when planning the roof terrace was watering. The idea for the terrace is for the maintenance to be mainly done by a group of volunteer staff who work on the ward; however, there is no access to water outside on the roof terrace itself.

Additionally, although the terrace is in a relatively sunny position, the left-hand side is shaded. Therefore, planting for shade was another element to consider.

After much consideration, we came up with the plan below. It is a little experimental and we will have to see how the plants take to the space over the coming year. But one thing to keep in mind when planning a border is that it will need adding to or altering depending on species preferences and the weather. You’ll need to be flexible with your plan and make alterations as the growing season continues, which is what we plan to do.

Southmead Hospital’s ICU roof terrace planting plan
Southmead Hospital’s ICU roof terrace planting plan
The assistant ranger prepares the drought-tolerant bed at Southmead Hospital, Bristol
The assistant ranger prepares the drought-tolerant bed at Southmead Hospital, Bristol. Photo: Phoebe Webster / Centre for Sustainable Healthcare 2021. Attribution 4.0 International (CC BY 4.0).
Drought-tolerant plants in the raised beds in the new ICU roof garden
Drought-tolerant plants in the raised beds in the new ICU roof garden. Photo: Phoebe Webster / Centre for Sustainable Healthcare 2021. Attribution 4.0 International (CC BY 4.0).
Drought-tolerant planters outside Southmead Hospital’s Cycle Centre

The Cycle Centre planters are small, raised beds that face north/northwest: a tricky design when incorporating the drought-tolerant element, as these Mediterranean plants are typically sun-loving. The planting varies between the planters to match the light and aspect, with sunshine-preferring plants in the westerly facing beds and the full shade plants being in the most shaded and northerly facing beds.

The species we have used here are:

I love the drought tolerant beds. They are beautiful to look at and I like knowing that they will last the coming temperature changes.

– Grace Kelsey Sustainability Projects Officer, NBT
NBT Cycle Centre drought-tolerant planting plan
NBT Cycle Centre drought-tolerant planting plan

How to incorporate drought-tolerant planting into your site

When creating any border, you will need to consider:

Soil

Heavy clay and a high water table can mean boggy or poorly draining soil; if this is the case, a ‘bog garden’ may be the way forward and not a drought-tolerant one. This can be easily checked by digging a 60cm deep hole and checking it for water everyday over one week. If water fills the hole fully or partially, it is likely that you have a high water table and should plant in accordance with this.

On the other hand, chalky, gravelly, or sandy soils are typically fast draining and prone to drought. While you can improve the quality of these soils by adding compost or manure twice a year, this is time consuming and costly, so a gravel or drought-tolerant style garden can reduce costs and workload.

Border type

Raised beds can be added into any location, such as courtyards, carparks and entrances, and can often be made into additional seating areas. Borders at ground level can follow the edges of open spaces or paths, or be grouped together to form ‘islands’ within lawns or courtyards.

Raised beds are most suited to drought-tolerant planting as the soil type can be specified, and the drainage is a lot better for Mediterranean plants. Using a mixture of soil and horticultural grit is a good way to add drainage; adding old building materials and bricks to the base of a bed can also work well.

Aspect and light

Aspect refers to the direction your garden is facing – vital when thinking about how much light the space will receive. A south-facing aspect will be sunny, and a north-facing aspect will have little or no direct sunlight. South or southwest facing spaces are great for drought-tolerant borders or raised beds. North-facing aspects will be shadier and harder to establish as a drought-tolerant space, as Mediterranean species usually prefer direct sunlight. Ferns that could work well in the space include Polypodium vulgare and P. setiferum; species that like drought and shade are available but take a little more planning. East-facing gardens will struggle with strong morning light and frosts, so be careful to avoid plants that flower in early spring.

Watching how the sun falls on a space and where shadows appear throughout the day is    also important when planning a border, and will create micro-climates within these spaces. Mark sunnier and shadier areas on your planting plan, and tailor your plants to fit this pattern. Shadier areas which are less suited to drought-tolerant plants could incorporate ponds or woodland-themed plants, which will bring in diversity.

Drought-tolerant plant species

Taking care of your drought-tolerant bed

Soil draws water up to the surface, where it then evaporates. Mulching the top of your beds prevents this by keeping the soil underneath cool and moist. This benefits all plants as their roots are kept moist, especially during dry summers.

It is best to mulch in spring, when the soil is damper and temperatures are still cool. Weeding prior to mulching is essential if your goal is also to supress the weeds that will come up in summer.

A mulch of gravel (such as grit or bark chippings) will last longer as a mulch and help finish off your borders. Using compost or manure will benefit the plants in other ways but will need replacing more regularly as it is drawn into the soil by worms.