Urban planters experiment

To build on our plant range suitable for urban schemes, we are have been trialing large containers and experimenting with different growing media and irrigation. 

A need for more suitable alternatives

This experiment was born out of conversations with city councils and those responsible for maintaining green public spaces, who expressed a desire to move away from and replace traditional bedding schemes with more sustainable, longer lasting alternatives.

Freestanding planters can greatly enhance urban spaces by bringing colour and life to areas where borders aren’t feasible. However, budget constraints, maintenance and limited irrigation can prove challenging with planters as they’re often being left untended for long periods of time. Large containers carry more visual impact and usually require less maintenance, as they’re less affected by rapid temperature fluctuation and, with a drought tolerant planting scheme, won’t require watering as often. The likelihood of hotter, drier summers, paired with an increased awareness of potential future water shortages, makes it essential to look at how we can preserve and better use our precious water resources.

Growing in sand

We have successfully grown in sand and other substrates for local projects (find out more here), which has helped us select a range of low maintenance, drought tolerant plants for such testing growing conditions.

Keen to help green up urban spaces and increase biodiversity in public areas but also wanting to inspire and help guide our customers, we set out to experiment with large planters, different growing medium and irrigation. In March, six months ago, three large, galvanized water tanks on our nursery were planted up, using a mixture of drought tolerant perennials, ornamental grasses and shrubs. Tried-and-tested plants were combined with some more unusual choices. The plants only received minimal watering and maintenance to see which ones performed well.

The plants needed to be:

• Drought resistant and survive on minimal watering
• Low maintenance
• Perennial i.e. come back year after year
• Have a long season of interest, not only look good when flowering
• Look good together
• Not outcompete each other

Drainage

The containers had drainage holes drilled in the bottom and sit propped up on a couple of wooden battens to ensure any excess water can drain away. At the bottom of each container there’s a 20-30cm drainage layer of pot crocks or similar. Two of the containers were filled with a mixture of our peat-free potting compost, sharp sand and grit (check with Ben F) and one was filled with sharp sand. A concrete planter, two small concrete blocks with holes  and a rubble pile of bricks and sand were also added.

Little did we know when we started this experiment six months ago that it would turn out to be the driest spring and hottest summer on record, truly putting the plants to the test.

What we’ve learnt and what we would do differently

Nearly all of the plants thrived, exceeding our expectations in the hot weather. We knew they would be extremely drought resistant, having grown most of them in the ground for years, but it was impressive to see how well they performed in a container with minimal watering. The size of the planters and the large amount of compost or sand greatly contributed to keeping the roots cool, stopping the plants from drying out as they only received minimal irrigation. The plants we lost were mainly due to being outcompeted by stronger growing neighbours.

It was interesting to see and compare how much the type of growing media affects growth. As expected, the plants in sand stayed more compact, with Stipa tenuissima displaying less floppy growth compared with when grown in peat-free compost. Frankenia thymifolia thrived in both growing media but grew at least twice as large when planted in compost and smothered most of its neighbours, highlighting the importance of not only choosing the right plant for the right place, in terms of drought resistance, but also selecting species and varieties that match in growth rate to prevent one from outcompeting the others.

To give instant impact the containers were fairly densely planted, with the intention of removing some plants if they became too crowded. Container 2 got too congested, so a couple of plants will need to be removed to give Stipa gigantea more room to grow.

Atriplex halimus, a large shrub in our Gravel Garden, is rarely used as a container plant but can be pruned hard each spring and trimmed again in summer to keep it more compact. It would have been better placed towards the centre of the planter, rather than in a corner, to achieve visual balance against the smaller plants.

The contrast in height was sometimes too great, with no mid-sized plants bridging the gap. Stipa gigantea, being tucked in a corner, could have done with a taller companion as Linaria ‘Peachy’ struggled to stay upright. Or perhaps we’ll move the grass towards the centre, allowing it to become the main feature.

Bulbs could be added to prolong the season of interest, ideally placed where their dying leaves don’t look messy or smother emerging plants. Eremurus ‘Cleopatra’ looked stunning in bloom, albeit only for a brief time. As its starfish roots can be sensitive to competition we’ll have to wait and see how well it does next year. Alliums with attractive seedheads would make a good alternative.

The (peat-free) soil level dropped a couple of inches during the growing season but can easily be topped up, or a layer of gravel could be added as a mulch, which would also help to conserve soil moisture.

The planter filled with sand received less sun than the other two, being slightly shaded by a roof. It should be moved into full sun for more accurate comparison.

Regarding maintenance, perennials such as diascia and oenothera look best if given a quick tidy in late autumn, trimming them back by two thirds but leaving enough protection over the winter, and any dead or struggling plants should be removed. Similarly to the gardens we leave most plants standing for as long as possible, with grasses and seedheads providing interest through the winter months, in additions to being beneficial to wildlife. In late winter or early spring, the shrubs (used here) can be pruned to shape and to reduce size if needed, while perennials and grasses should be cut back before new growth emerges.

We’ll continue to experiment with new containers, different plants and combinations next year, to build on our plant range suitable for urban schemes.

Watering

Listed below are all the times we have watered this container display since its initial planting 10/03/2025.

A 7-litre watering can was used on the large containers. The smaller concrete planter was added in May and received very little water, but no record was kept. The rubble pile and two small concrete blocks didn’t receive any watering, relying on rainfall only.

Hexagon concrete container (added in May)

Frankenia – Looks great spilling over the edge. Strong growing and quickly outcompeted most of its neighbours - in a year’s time it’ll fill the entire space. More slow growing in sand.

Limonium bellidifolium – looks great but needs pairing with a less rampant companion.

Container 1

Atriplex halimus – performed well but will outgrow the other plants in this container unless clipped. Perhaps better used as the main focal point, underplanted with lower plants.

Eremurus ‘Cleopatra’ – attractive flowers but not long enough season of interest to earn its place in a container. It’ll be interesting to see if it flowers again next year.

Euphorbia seguieriana – useful long-flowering spurge. Rather lax habit. Would have stayed more compact if planted in sand.

Hormathophylla spinosa ‘Roseum’ – too small to make an impact. It struggled with the competition from stronger growing plants and would be better in an alpine trough.

Oenothera lindheimeri – would have benefitted from a 'Chelsea Chop' to keep more plants more compact. This method can also be used to stagger flowering time, if using more than one plant. Floriferous, blooming over a long period, especially if dead-headed. Would have benefited from more water, showing signs of stress during the heatwave, but should be fine once the roots have sought deeper into the soil.

Pseudodictamnus mediterreaneus from Crete - a small leaved, more compact form of the species with a neat dome-shaped habit. Prune after flowering or in early spring to keep its shape.

Salvia rosmarinus ‘Roman Beauty’ – nice and compact with deep green foliage and trailing habit. Looks good spilling over the container’s edge.

Teucrium x lucidrys – this is not the ground covering form we grow in our Gravel Garden. Mound-forming but equally attractive and drought tolerant.

Thymus sp ex Turkey – an excellent strong growing thyme, forming a dark green carpet. Not suitable for a small container.

Veronica umbrosa ‘Georgia Blue’ – does better in the ground, where it forms a low carpet.

Container 2

Crithmum maritimum – This edible umbellifer makes a nice addition to any drought resistant scheme with its attractive succulent, grey-green foliage. Flowers were smaller than usual. Struggled during the heatwave, perhaps due to being recently planted, but quickly recovered once temperatures returned to normal.

Diascia barberae ‘Ruby Field’ – long flowering time, producing a second flush of flowers if cut back after flowering. Can look a bit untidy if not cut back. Diascia integerrima is stronger growing.

Erigeron karvinskianus – long flowering time. Prolific self-seeder.

Linaria ‘Peachy’ – lovely colour but struggled to stay upright, so better in a border where the wind doesn’t knock it over.

Origanum ‘Kent Beauty’ – struggled with the competition from stronger growing plants. Better in an alpine trough.

Salvia rosmarinifolia ‘Miss Jessopp’s Upright – good vertical but the plant was a bit leggy and would have benefited from an initial prune to make it bushier at the base.

Stipa gigantea – can look great in a large container. Needs more space to grow so some of the other plans will have to be removed. Too much of a height difference between the flowers and the rest of the plants.

Stipa tenuissima – looks good but would have stayed more compact if grown in sand. Self-seeds prolifically.

Thymus longicaulis -  the stronger growing Thymus sp. ex Turkey would be a better alternative for a container this size. Not suitable for a small container.

Container 3 with sand

Acaena saccaticupula ‘Blue Haze’ – slowly spreading, a charming groundcover

Euphorbia myrsinites – its trailing, glaucous foliage makes a great pairing with the orange blades of libertia.

Frankenia thymifolia – excellent, strong growing ground cover. Slower-growing in sand compared with plant in compost-mix.

Helichrysum stoechas ‘White Barn’ – not much growth in the first season but given another season it should form a nice silvery mound.

Hertia cheirifolia – slightly spreading habit. Didn’t produce many flowers this year but has an interesting foliage.

Libertia peregrinans – looks very happy and healthy but didn’t put on much growth. Its orange-tinted leaves contrast beautifully with grey and green foliage.

Origanum vulgare ‘Compactum’ – struggled and would be better in the ground

Thymus longicaulis – looks good spilling over the container’s edge. Grown in sand it stays more compact.

Verbena officinalis var. grandiflora ‘Bampton’ – stunning dark foliage, later fading as the season progress and a haze of flowers over a long period.

Rubble pile

Galactites tomentosus – biennial and didn’t establish well. Would have been better to scatter seeds onto the pile.

Stipa tenuissima – did well but self-sown plants will be much stronger growing

Verbascum bombyciferum – died. Would have been better to scatter seeds rather than trying to transplant.

Eschscholzia californica – seeds germinated and produced healthy looking plants.

While some plants struggled or completely disappeared others, such as Centranthus ruber and papaver, spontaneously appeared and thrived.

Small concrete blocks

Sedum dasyphyllum

Sempervivum ‘Reinhard’

Looked pale and would have benefitted from some water during the extreme heat. The plants regained their colour when conditions cooled down. They’ll need dividing to prevent them from becoming congested.