how to keep blue hydrangeas blue

How to Keep a Blue Hydrangea Blue

How to Keep a Blue Hydrangea Blue

Most plants grow on most soils, however some need specific types of soil to thrive. Rhododendrons, azaleas and other ericaceous plants will not grow on alkaline soils; they need acid conditions. If they thrive in your garden or surrounding gardens, your soil must be acidic. If the leaves of rhododendrons turn yellow, or they are missing from the neighbourhood your soil is probably alkaline. Your soil type not only influences what you can grow, but it can also have an effect on the leaf and flower colour of some plants: hydrangeas are a well-known example.

Some varieties of hydrangea are blue or purple when grown on acid soil and pink or red in alkaline soil conditions. So if you plant a lovely blue lacecap or mophead hydrangea in the garden, and your soil is neural to acidic, it will produce blue flowers year after year. If you plant it on alkaline soil the following year it will flower purple-red or pink, even if it was clear blue when you bought it.

In the open ground it is difficult to maintain those blue flowers, but it is possible if you grow it in a pot; hydrangeas make excellent subjects for pots and containers. Choose a nice big, deep pot, at least 40cm (15”) in diameter. Plant it in a lime-free growing medium, Vitax Ericaceous Compost is ideal. This is specially formulated for rhododendrons, azaleas and other lime hating plants and will be perfect for your hydrangea if you feed it regularly.

In hard water areas regular watering tends to make the growing medium more alkaline, even if it starts off lime free. So, to make sure your hydrangea stays really blue add Vitax Hydrangea Colourant, a powder containing aluminium that you can mix with the compost. You can also mix a little into the soil surface each spring and add it to the can when you water your plant.

Incidentally white hydrangeas do not change colour according to soil type, but they may blush pink in the sun. 

Feeding and watering

Hydrangeas hate dry conditions, so regular watering is essential in pots and containers, and in dry spells in the open ground. Add plenty of garden compost or farmyard manure when you plant your hydrangea in a bed or border and make sure you water thoroughly before and after planting.

Although they are not particularly demanding, hydrangeas need a supply of food in the soil to promote growth and flower production. An annual application of Vitax Conifer and Shrub Fertiliser is ideal in the open ground and in pots and containers. This is perfect for acid-loving plants so will not influence the colour of your hydrangea.

Andy McIndoe for Vitax website 2016 

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