Lessons from the drought

Going, going, gone. Rosemary at the fare end of the planter in June, July and at the front of the planter in August

A few months earlier:

Rosemary thriving in February, kniphofia looking great in May with the Shard behind.

I thought that the huge Rosemary bushes and Salvia ‘hot lips’ that I’d inherited when I took over the maintenance of two large planters on the roof of 1 Bread Street, in the City, were completely drought-resistant. They had thrived in 2021 with just rain water, and at the beginning of 2022 were looking magnificent. But after the driest spring and summer since 1976, they were dead by July, and the Kniphofia (Red hot pokers) also looked dead, along with Nepeta (Cat mint), Rose campion (Lychnis coranaria), and Verbena bonariensis.

The reason I didn’t install an irrigation system after the very dry spring was twofold:

  1. I thought it would start raining and the drought-resistant plants on the roof would bounce back
  2. When it was obvious we were in the middle of a long drought, the intense heat prevented me from venturing up on the eighth storey rooftop in the City surrounded by concrete, steel and glass. It wouldn’t have just been the plants that would have expired!

So I’m afraid, I let that abundant source of nectar and pollen perish. It was heart breaking when I finally got back up to the roof to see the devastation.

In August, the heat abated and we were able to install a timed, sprinkler irrigation system. A few days later, it finally rained! But it was too late to rescue the Rosemary, Salvia, Nepeta and others. Only the sedums, thank goodness, lived up to their reputation and withstood the drought without any problems, and I added more.

Timed sprinkler system installed, sprinklers placed in planters, but only the sedum appeared to survive.

In September, myself and my new friend and now colleague, Alex – who is extremely knowledgeable about plants and an experienced gardener – agreed to help me remove the dead Rosemary, salvia and other plants, and replace them. One day a week for a month, we cut and pulled, and lugged bags of dead woody branches.

The rain and the watering system did help the Kniphofia, a tough plant from South Africa, bounce back. But it also encouraged ‘weeds’ to spring up all over the planters. I know weeds are just flowers in the wrong place, but they really had to go. Luckily my client was very understanding. And it’s a roof that staff don’t have access to, so aesthetics aren’t as important as they would be if it was accessible. The client is paying for the planters to be full of plants that feed bees throughout the spring and summer and early autumn.

We replaced the dead plants with a variety of bee-friendly plug plants and 2 litre pots hoping they will take and grow by next spring and summer.

New additions included: Calamint, lavender, Teucrium hircanicum (Caucasian germander), Origanum, Eupatorium, Veronica, Nepeta and Stachys byzantina (Lambs’ Ear) (all supplied by Rosybee) , along with 2 litre pots of late-flowering plants including Russian sage (Perovskia atriplicifolia), Tickseed (Cereopsis), Globe thistle (Echinops), Nerine (Nerine bowdenii) and Agapanthus – some of the latter had survived the drought. We also planted new creeping Rosemary plants, but it will take years before they reach anything like the size of the ones that died.

We mulched around the new planting, to suppress the weeds and to protect the plants from excessive rain we may get this winter, and to keep their roots warmer . We turned off the watering system for winter.


  1. It’s essential to have an irrigation system installed for planters on a rooftop, even if the plants are drought-resistant, unless you are being paid to water frequently in dry spells.
  2. The planters I inherited are only 20cm (200mm) deep and not all of that is soil. There is a layer of soil, a fleece and a layer of lecca for drainage below the fleece. The lack of depth of soil played a part in the Rosemary’s demise. If it had had deeper roots it may have been able to cling on. I would recommend planters with 400mm depth of soil for plants to thrive.
  3. Visit rooftop planters more often to assess the conditions of the planters.
  4. Take preventative action more quickly.
  5. South African plants like Kniphofia, Agapanthus and Nerine bowdenii, a late flowering lilly, are extremely tough, drought-resistant plants they don’t mind windy exposed conditions, full sun and no water. There may be others I’ve yet to discover….

Watch this space to see how the planters are looking in 2023.

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