(Editor's Note: This article was originally published on September 6, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
A short while ago I wrote praises about grape hyacinths (Muscari) being an indispensable source of blue colour in the spring garden. It seemed appropriate that I should also write about the merits of squills and their close relatives, the other main group of blue-coloured, spring flowering bulbs. For completeness, I will include in this article the true squills (Scilla), bluebells (Hyacinthoides), Lebanon squill (Puschkinia) and glory-of-the-snow (Chionodoxa). Like the grape hyacinths, most of the squills also hail from the Mediterranean area and Asia Minor where they inhabit open meadows, woodlands and alpine slopes. In the garden, the vast majority are easy to cultivate as long as the soil is well-drained and as many are quite vigorous, they lend themselves to naturalizing. Full sun to part shade is best and the bulbs should be planted about 10 cm deep. Always plant them in groups for the best impact.
The true squills, from the genus Scilla, contains some 30 or species although we generally grow just a couple in our gardens. By far the most popular is Siberian squill, Scilla siberica. It is perhaps the most prolific of the whole lot, self-seeding with abandon. Plant a cluster of bulbs and you'll have a drift in a few years! The standard selection is ‘Spring Beauty' with pendant, somewhat star-like, deep blue, scented flowers. There is also a white form called ‘Alba'. Less common is S. bifolia with smaller, upward-facing, star-shaped flowers which are produced along a one-sided spike. Its blooms are violet-blue but both white-flowered (‘Alba') and pink-flowered (‘Rosea') cultivars exist. The other readily available species is S. mischtschenkoana, known incorrectly in the trade as S. tubergeniana. This species is slower to multiply but each bulb will produce several flower stems with outward-facing, fragrant blooms which are white with pale blue stripes (essentially a Puschkinia on steroids!). Lebanon squill, Puschkinia scilloides (aka P. libanotica) is, from the species epithet, very Scilla-like. They produce a loose, conical cluster of pale blue flowers with darker blue stripes. All of the above species are rated for zone 3 and will reach about 15 cm in height.
Scilla siberica and S. siberica 'Alba' along with S. mischtschenkoana
Scilla bifolia 'Rosea' and Puschkinia scilloides
Once known as Scilla, but now placed in the genus Hyacinthoides, are the bluebells. We grow two main species; the English bluebell (H. non-scripta) and Spanish bluebell (H. hispanica aka H. campanulatus). Both grow to about 30 cm with spikes of nodding, bell-shaped flowers. They bloom about a month later than the true squills. The English and Spanish bluebells look quite similar but the flowers of English bluebell are one-sided on the stems while those of Spanish bluebells are arranged around the stems. English bluebells are typically blue but white and pink-flowered selections exist. The Spanish bluebell is probably more common in the North American trade and have three main selections: ‘Blue Queen', ‘Rose Queen' and ‘White Lion'. Bluebells are rated for zone 3 and actually prefer soil that stays moist, even during the dormant season. Unlike the true squills, bluebells lack the protective skin that helps maintain bulb moisture during the dry dormant season. Very closely related to the bluebells is Brimeura amethystina, commonly known as Spanish hyacinth. It is a smaller, more dainty bluebell look-alike with white or blue bells. It is only rated to zone 6 and probably best purchased from specialist bulb nurseries.
Spanish bluebells come in standard blue, along with white and pink forms
English bluebells and the Spanish hyacinth
The other large group of blue-flowered spring bulbs are the glory-of-the-snow, Chionodoxa. However, in this group, their blue colour is lighter with violet tints, rather than the true blue of squills and bluebells. There are four main species, all which are hopelessly confused in the trade. The standard species is called C. luciliae but I have purchased this species only to end up with the other three species which are C. sardensis, C. forbesii and C. lochiae. I still don't have a real C. luciliae! So how do the species differ....not by much! The true C. luciliae has only 1-2 flowers per stem and are soft violet-blue with a small central white zone. C. lochiae has 2-4 flowers per stem, are also soft violet-blue but either lack the white ‘eye' or have one which is quite pale. Most of the Chionodoxa in the trade are actually C. forbesii. This species has up to 12 flowers per stem, are bright blue with just the slightest violet tint and have a large distinct white ‘eye'. There are also white-flowered (‘Alba') and pink-flowered (‘Pink Giant') selections. The last species, C. sardensis, also has bright blue flowers which are more outward-facing (the others are more upward-facing), smaller in size and lack the central white ‘eye'. Hopefully the accompanying pictures will at least clarify C. lochiae, C. forbesii and C. sardensis. Unfortunately I could not find a picture of the real C. luciliae. All are rated to zone 3 and are the earliest-blooming of the blue-flowered spring bulbs. Finally, to complete the picture, there is X Chionoscilla allenii, a natural hybrid between Chionodoxa forbesii and Scilla bifolia. The flowers are deep blue and tend to look more like the Scilla parent.
Comparison of C. forbesii, C. lochiae and C. sardensis. Essentially C. luciliae looks like C. forbesii but has only 1-2 flowers per stem.
Chionodoxa forbesii 'Pink Giant' and 'Alba'
I hope this article and the previous one on grape hyacinths, will stimulate you to try growing this wonderful group of lesser spring bulbs. I cannot even imagine a spring garden without them.
Naturalized displays of Glory-of-the-Snow and Siberican Squill
I would like to thank the following people for the use of their pictures: evert - closeup of Scilla siberica; TBGDN - Hyacinthoides hispanica; mhansen - Hyacinthoides hispanica (white form) and toxicodendron - closeup of Chionodoxa forbesii