A lot of Lithuanian gardeners are very fond of rhododendrons, which have become rather common, but they really are irreplaceable when one needs a colourful and evergreen plant to decorate a shady spot. Most rhododendrons are native to East and Southeast Asia, where summers are damp and rainy, and winters are snowy. In their natural habitat, rhododendrons grow on humus-rich and porous soils. Wild groves of rhododendrons can also be found in North America and Europe.
Rhododendrons came on to the garden scene some 300 years ago, and since then they have become one of the most popular ornamental plants. Associations of professional and amateur rhododendron growers sprung all throughout the world – Germany, Great Britain, America, Australia, New Zealand. More that 1000 cultivars of outdoors rhododendrons have been created in a relatively short time.
Rhododendrons require acid soil (pH 4.5-5.5). When cultivated on alkaline soil, they grow slowly, flower poorly, and soon succumb to diseases and pests. Calcium, absorbed by the plants, inhibits utilisation of other nutrients (potassium, magnesium, iron), therefore the plants loose vigour and their new growth become stunted.
Several species of rhododendrons, such as hairy alpine rose (R. hirsutum L.), rusty-leaved alpine rose (R. ferrugineum L.) and Kamchatka rhododendron (R. camtschaticum Pall.), can be successfully grown on alkaline soils. Cultivars, belonging to the INKARHO group, which currently includes over 250 varieties, have become popular recently due to their beauty and ability to grow well on alkaline soil. But they dislike heavy clay soil, and are 
best planted in fertile ground, amended with some peat, and enriched with sufficient nutrients. These rhododendrons are fairly low-maintenance, and they do not need to be mulched with acid peat each year.
One way to increase acidity of the soil is to mulch plants with peat moss or conifer needles. You could also try using sulfuric acid: dilute 5ml of concentrated sulfuric acid in 10 litres of water (make sure, you put acid into the water, and not the other way round). Apply a few times during the growing season. If rhododendrons are grown in less than favourable conditions, it is strongly advisable to mulch and fertilise plants using only organic matter, such as pine needles, pine bark, oak leaves and peat moss.
© Mygarden.lt, 2009
Hello Giedra, I love the beautiful pink Rhododendron. I’ve just started to fall in love with this Genus. We grow mainly subgenus Vireya. But we live at Tamborine Mountain in South East Queensland Australia. We can grow the cold Climate ones here too. This is where Temperate climate meets sub tropical.
