For many gardeners, true blue is one of the most treasured colours in flowers, but it can be a fickle one to acquire unless you actually buy the plant in bloom in a garden centre.
Even then, hydrangeas, for example, may not remain their original heavenly blue when they sample conditions in your home garden. Those beautiful blues of the mophead Endless Summer and its companions need acidic soil, and if they don’t get it, next year’s petals will have turned purplish. Adding aluminum sulphate to their soil every spring is the usual way of maintaining blue in hydrangeas.
There are other pitfalls too: many “blues” contain a hint of purple but are often described as blue perhaps because it mirrors catalogue and online descriptions. Also photos of “blue” flowers are not necessarily accurate. Nor are names. English bluebells, for instance, are among those that are almost blue but not quite.
For an easy way of gaining lakes of blue, you can to turn to spring bulbs. Scilla sibirica is a deep, true blue, dwarf long-flowering bulb that spreads fast under trees where grass is thin. It’s inexpensive, and virtually all garden centres routinely offer it in fall.
Chionodoxa forbesii is blue and white (but comes in other colours, too), but its cousin Chionodoxa sardinensis is a deep, startling blue and a very dwarf eager spreader with large globe-shaped seedheads so convenient to plant in other places too. However, it’s not widely offered.
Rural gardeners who want a spring carpet of gentle sky-blue still turn sometimes to forget-me-nots. Once the blue deluge is over, they wait for the heads to set seed, then yard the old plants out, secure in knowing forget-me-nots will reappear again next year..
That’s the good news. The bad news is that successive generations develop smaller flowers and get weedier because they gradually revert to the wild form.
When summer comes, one of the easiest-going blue explosions comes from Anchusa azurea (Alkanet). It produces a metre-long flowering pyramid of intense blue that is said to bloom from June to September if you deadhead it.
It’s ideal for gardeners with dry sandy/gravelly/rocky soil where it will perennialize and reportedly be almost impossible to remove. Unfortunately, it hates soggy clay and tends to die over winter if you don’t give it good drainage.
It’s easy from seed, which you may have to get online. Anchusa capensis is a cousin and the one where you can find seed in garden centres. It has paler but nice, blue flowers, is an annual and dwarfer 45 centimetres high.
Better known for intensely blue flowers are some of the gentians. One standout is Gentiana acaulis, a very dwarf trumpet gentian available most springs in garden centres. It’s a temperamental one, and soil recipes abound, but generally a sun/shade mix of gently acidic soil with humus and grit is at least a place to start.
Gentians are a huge tribe that come in a range of blues and a few which aren’t blue at all.
Some beautiful blues may be found in seed-grown annuals. Much of the seed though is often sold in mixes of colours these days. Varieties include larkspur, lobelia, delphiniums and nigella.
Anne Marrison is happy to answer garden questions. Send them to her via firstname.lastname@example.org. Please add the name of your city or region.