Jo Arnell explores how biennials are the often overlooked heroes of a successful planting scheme

Imagine a plant that looks after itself, one that will flower early, that will grow in difficult shady situations, that after flowering will quietly, sometimes even decoratively, set seed for the next generation and then bow out, and allow summer flowers to take centre stage. Well, I give you, ladies and gentlemen, the biennial. A national treasure if ever I saw one. While we are busy trying to coax our pampered and expensive garden centre lovelies into bloom, up they pop, asking for nothing, giving masses and, once established, rewarding us year after year. I have found myself complaining about the cheerful abundance of some of them (yes, you, forget-me-nots), but would never be without them.

So what exactly is a biennial? The clue is in the name, in that they flower every other year, bi-annually. Ostensibly they are annuals, but they spread their flowering season over two calendar years – from summer to the following spring, instead of from spring until autumn. Biennials owe their existence to the changing of seasons – and the fact that the leaves fall off the trees as winter approaches. The consequence of the trees staying bare until April is a leafless chink of light in early spring where the biennials have found a niche, opportunistically blooming before the canopy of leaves closes over them. They are the natural colonisers of woodland glades and hedgerow edges, adapting their lifestyle to the sequences of light and shade. It is for this reason that a biennial will germinate and grow a whorl of basal leaves during the first year – to be ready to burst into flower early and make the most of the spring sunshine. This makes them ideal for growing in tricky areas of the garden; many, like foxgloves, forget-me-nots and honesty, seem to positively enjoy dry shade, so will grow under trees, on the shady side of walls and other bleak, godforsaken places (and we all have our share of those).

Good Companions

Biennials are excellent plants to grow among spring bulbs; they flower at around the same time and can be used to contrast, harmonise or generally enhance the appearance of a spring display. If you love tulips – and most of us do – you may not love their large and floppy leaves quite so much. A frothy skirt of forget-me-nots or eye-catching counterbalance of honesty will do a good job of hiding, or distracting, from the less than lovely tulip leaves – that must be left on to strengthen the bulbs for next year. Be careful not to let the biennials swamp emerging bulbs and young perennials though, as they will do a good job of blocking light as well as fading bulb leaves and may overwhelm other young plants. Forget-me-nots in particular can enthusiastically smother emerging perennials, so may need thinning and weeding out.

Self-sowers

Biennials have a (mostly) welcome habit of self-seeding, so you should only need to sow them once. You can allow them to self-sow – often they will find the very best places for themselves and grow away more strongly than those you have carefully planted. Depending on your style of gardening – which may be related to the time you have available, the self seeders can be managed in two ways, or in a combination of the two. The first is to allow nature to take its course and let the plants self-seed where they like. This way many serendipitous planting combinations can occur, with plants finding exactly the right places to grow, often in situations you would never have positioned them in – and sometimes in far better ones. This works best if your garden is fairly weed-free, if not, you will need to be able to identify your plants at an early stage and try to separate the weedlings from the seedlings. Most self-seeding plants germinate best in free-draining soil, and will struggle on heavy, claggy clay. Try to open up the structure of clay soil by incorporating organic matter and grit. Self-seeding then becomes a happy accident and looks natural and unforced. The problem is that the plants are choosing where they want to grow and this may not be where you would plant them. Judicious weeding becomes the order of the day – and this is sometimes harder than it seems; there’s something unkind about weeding out healthy, happy plants, even if they are growing in the wrong place.  

Methods of seed dispersal vary wildly and evolution has come up with some ingenious methods for this. Many seed capsules are triggered to literally explode, because the purpose is to propel the seeds as far away as possible. This can make collecting seed frustrating, as the timing in some situations needs to be just right – collect too early and the seed won’t be ripe, collect a second too late and the capsule has burst and hurled its contents to the wind.

The other method is to collect the seed and sow it yourself – either in pots to plant out later, or in situ. Labour intensive, but keeps you in charge of the show. A few very basic pieces of equipment are needed; paper bags or envelopes, a pen for labelling, kitchen paper for drying, a sieve or sheet of paper for separating seeds from the pod – and a nice dry, windless collecting day.

Biennials are hardy plants and are sown in late spring to midsummer – you can sow the seed into a pot or seed tray, or directly into the ground. I often find a bit of space in the veg patch and sow a few rows of foxgloves, Sweet Williams or wallflowers into a sort of nursery bed. Once the seedlings emerge, thin them out to give each one a bit more room to grow. In the autumn they can be carefully  lifted and transplanted to the place where they will flower in the following spring.

Packed with nectar

I would happily grow biennials for their sheer charm, but they are very good for wildlife too. Biennials are brim-full of nectar – they are insect pollinated and their only job is to set seed as soon as they can, so they make it as easy as they can for the insects – many are scented to lure in a wide range of creatures including night pollinators such as moths and beetles. Flowers like foxgloves even advertise the route to their nectaries with little bee landing strips – often in the ultra-violet end of the spectrum and not always visible to us, but look closely and you will see the speckled insides of the tubular flower is indefinite rows leading deeper inside. Biennials appear just as insect numbers are building up and this coincides with the main bird nesting season. Give the insects plenty of nectar and you will also be feeding the birds. 

Beautiful Biennials
Foxgloves (Digitalis) – graceful tall spires, very useful for shady positions.  The native foxglove is usually mauve-pink, there is also a beautiful white form, Digitalis alba and cultivars in shades of apricot, pink, mauve and cream. Some are short-lived perennials and will last longer than two years.
Forget-me-nots (Mysotis) – a froth of tiny blue flowers – they will spread all over your garden if you let them. Looking pretty under tulips, forget-me-nots will provide a veil to cover their foliage. Pull up after flowering and to thin out if they are swamping other plants.
Wallflowers (Erysimum) – another good spring companion for bulbs. Available in lots of colours, wallflowers are spicily scented. Sow them yourself, or buy as bedding and plant out in the autumn.
Sweet William (Dianthus barbatus) – related to pinks, these often gave charming bi-coloured flowers with frilled edges
Brompton stocks (Matthiola incana) – highly scented spires of flowers in pastel shades, these can be biennial or short-lived perennials. They will need a sheltered site and winter protection.
Honesty (Lunaria annua) – these pop up in purple sort white and are useful for their pale and delicate papery seed-heads too.

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