I'm a garden expert - hydrangeas will grow a beautiful bright blue if you do 1 thing

Hydreangeas need one key thing to retain their deep blue hue, an expert says. The flowers, which are native to Asia and the Americas, can produce petals of various shades, including blue, pink, white, and sometimes even green.

However, as plant lovers know, their vibrant colours can fade without proper care. Emma O'Neill, head gardener at sustainable gardening charity Garden Organic says for blue hydrangeas, the soil is key.

Speaking to Express.co.uk, she explained that hydrangeas generally prefer partial shade, "but some varieties will tolerate more sun".

"They all need moist, well-drained soil," Emma said.

"The PH of your soil needs to be 5.5 or below to grow specifically blue hydrangeas, which is considered acid soil. This is so the plant can absorb the aluminum, which keeps the blooms their lovely hue."

"Pine needles around the base of the plant can increase the soil's acidity: some gardeners swear by coffee grounds, (but the effects are anecdotal).

However, she said the charity "would recommend you only plant blue hydrangeas if your soil is already acidic".

"Or, grow them in a container, in peat-free ericaceous compost, where you can control the soil conditions," Emma added.

Ann Marie Hendry, one of the writers at GrowVeg.com, says the plants can also benefit from radiated heat.

Speaking to the Express this week, she said hydrangeas "often grow best next to a building or wall where the radiated heat helps safeguard new growth from frosts in spring".

However, she added that "it's important to make sure the soil doesn't get too dry in summer".