Diarmuid Gavin’s guide to hardy hydrangeas

Here’s how to propagate, prune and protect these beautiful plants from disease

Colourful hydrangeas are beautiful, low-maintenance additions to any garden

A painting of a striking hydrangea by Corrina Earlie

Colourful hydrangeas are beautiful, low-maintenance additions to any garden

A painting of a striking hydrangea by Corrina Earlie

Chickweed

Verbascum ‘Violetta’

Colourful hydrangeas are beautiful, low-maintenance additions to any garden

Diarmuid Gavin

June 18 2022 02:30 AM

The wonderful artist Corrina Earlie sent me a picture of a hydrangea recently, a flower taken from her mother-in-law’s garden in Lahinch, describing its most deep-plum aubergine colour which she had to paint. The painting is beautiful, and it’s colour set me on a quest to find out which one its was. I’d never come across this colour before in a hydrangea and asked Instagram. The answer came from gardener Ali Rochford, who’d seen one growing in Dublin Zoo. It’s called Merveille Sanguine .

This is a mophead hydrangea. The colour may vary depending on your soil’s pH. White hydrangeas won’t change, but most other colours can. The more alkaline the soil is, the pinker the flowers will be, and extremely acidic soils can lead to red shades. I reckon Earlie had a hydrangea from a bush prone toward a purple colour, but planted in an acidic part of Lahinch has provided the deepest purple hue!

A painting of a striking hydrangea by Corrina Earlie

I found the bluest type in an amazing, windswept garden, Boolakeel in Ballinskelligs, where there’s a lengthy avenue of them planted on a glorious slope down to the sea. They’re sky blue and up to three meters in height, demonstrating their great use as a coastal plant.

Hydrangeas are suitable candidates for propagation by cuttings, so here’s a few tips to help you along. Softwood cuttings taken in early spring, when the plant has started to grow, is a good time — you want to select fresh, soft, new growth.

Early in the morning, when the plant is full of water, is the best time, and immediately pop them into a plastic bag. The main thing to avoid is the cutting drying out — once it does this, it won’t be successful, so try to get it potted up immediately.

Cut just below a leaf node, where there is a high concentration of growth hormone, and strip the rest of the cutting of the leaves, except for the top leaves. Again, this will help the cutting retain its moisture, as most water is lost through its leaves.

Dip in hormone powder and gel and place in cuttings compost. Water the compost and make sure it doesn’t dry out. A propagator unit with a heat bottom of 21C will speed up root development, but you could also cover the cuttings with a plastic bag and place somewhere warm, but not in direct sunlight. In around 10 weeks, hopefully it will have rooted successfully.

Hydrangeas are usually pretty low-maintenance, but sometimes you may observe brown spots on the leaves. It’s a leaf-spot disease, which can be either a bacterial or fungal infection. It can happen when in high humidity, when it’s warm and moist and there is little air flow. If you get it early and it’s affecting just a few of the bottom leaves, you can remove these, and sometimes that stops the spread. Otherwise, be careful how you water. Direct the hose at the base of the plant and try not to water overhead.

Another common problem is hydrangea scale insect. If you observe white, fluffy stuff on the stems of your plant, this is most probably the cause. The adult lays its eggs on the stems and covers them in this protective, white, waxy substance. Though the eggs hatch in the summer, the waxy stuff lingers. These insects then suck the sap from your plant, weakening the flowers and foliage. If the infestation is very bad, you may have to get rid of the plant, but you can try to tackle it by cleaning the plant with a soapy solution next spring and summer to remove fresh eggs, and by spraying with a pesticide or organic pest control during July when the eggs are hatching, paying special attention to the undersides of the leaves.

How to prune hydrangeas is one of the most common queries. Ideally, just leave the blooms on over winter to protect next year’s flower buds from frost. It can look a bit messy, but it’s worth waiting. Then, in spring, prune back to a couple of healthy buds, and as your plant is getting on, maybe some rejuvenation pruning will help — completely remove about one-third of all stems right back to the ground and remove any dead or diseased growth.

Plant of the week

Verbascum ‘Violetta’

Verbascum ‘Violetta’
Verbascums are good choices for dry gardens as they will tolerate drought but produce these wonderful, tall spikes covered in flowers. Violetta is a delicate and elegant variety with unusually deep purple flowers and looks beautiful in a herbaceous border or cottage-style planting. It would also suit a gravel garden.

Reader Q&A

Can you give me some advice how to get rid of chickweed, as the garden is covered in it?

Michael

Chickweed

Chickweed is a very common wildflower in Ireland and very prolific. The seeds can lay dormant in the soil for decades but can be woken from their slumber when you are digging or hoeing the soil. This exposes the seeds to light and they germinate. If it’s crowding out your plants, I would recommend regular uprooting of the offenders, and it’s much better if you can catch them before they flower and set seed. Mulching in your flowerbeds will also help suppress growth.

Submit your gardening questions to Diarmuid via his Instagram @diarmuidgavin using the hashtag #weekendgarden