Meconopsis, apart from Meconopsis cambrica (Welsh Poppy) are Himalayan plants and need cool, moist but well drained soil. They cannot stand strong wind, hot dry air and need light shade. They are also heavy feeders and need an organic rich soil with well-decomposed organic material incorporated under the plant. I prepare the site by digging out at least a cubic foot for each plant, incorporating well-rotted manure and then replacing the soil. The good blue colour in the blue poppies will only develop if the soil is acid. I tend to feed extra inorganic fertiliser as well, using Phostrogen Acid Plant Food and Tonic. The leaves of the blue poppies seem particularly prone to damage if planted in the wrong position. Strong wind will break them and I have seen damage where sunlight shining on rain droplets has burnt the leaf. In dry air and warm conditions no amount of watering may prevent the plants wilting and causing subsequent damage to the leaves. The flower buds do seem to emerge relatively early in the year and so frost pockets should be avoided.
The rosette forming species do seem more inclined to winter rot. In their native habitat they experience cold winters under a snow cover. British winters that are mild and damp may cause crown rot at the top of the taproot.
In all species the intention is to plant in a well-drained soil which remains moist and which is high in humus content.
Some of the very beautiful species are monocarpic ie. they grow for a number of years, flower and then die. They tend to form rosettes pf leaves with a deeply penetrating tap root beneath. It is my experience that some of these species can be more prone to crown rot than the fibrous rooted species such as the blue poppies.
Growing From Seed
To grow from seed I sow in early spring on the surface of peat and grit compost. They are kept cool (under 70 degrees Centigrade) and in the shade. I keep the moisture level up by hand misting daily. Under these conditions I would expect most to germinate in 2 to 3 weeks. They should be pricked out early. The stage after germination is the most critical, they may damp off and fungicide is apt to concentrate in the leaf hairs and kill the seedlings. It would appear that when they are very young, perhaps at the one true leaf stage they are very sensitive to night time temperatures. Night temperatures over about 16º Centigrade (60º Fahrenheit) will kill them and it is probably this and not damping off that causes most of the casualties.
Fortunately in the UK we can sow in autumn and overwinter as small seedlings. This may make it easier to keep nighttime temperatures below the critical level.
Meconopsis betonicifolia is the most common but Meconopsis grandis is superior, larger and bluer flowers. However M. grandis is not as tolerant of dry air.
Christopher Grey Wilson - Poppies (Batsford 1993) A relatively easy book to find and covers many of the Poppy family not just Meconopsis. Superb colour illustrations. Well written and well set out.
James Cobb - Meconopsis (Timber Press 1989) Now out of print and only available through firms that deal with out of print books. Another beautifully illustrated book with excellent line drawing that helps with identification and wonderful colour photographs.
George Taylor - The Genus Meconopsis (New Flora and Silva Ltd 1934) Difficult to find but this is the "classic" Meconopsis book. Very detailed with line drawings, distribution maps and some black and white photographs.