How to: grow perennials from seed
I have been sowing seeds for as long as I can remember. The move from a flower farmer to a seedmonger was a natural and a happy one, simply because I adore seeds so much. They are specks of hope, of potential, or dormant happiness, just waiting to be awoken.
I started, as I would suggest everyone does, by sowing and growing annuals. Lovely, easy, throw and grow, annuals, These are flowers that germinate, grow, flower and die within a year. Confusingly, sometimes not within the same calendar year (autumn sown hardy annuals will flower in early summer the next year) but it will be just under twelve months from start to finish with them. What they lack in longevity, they make up for in fecundity. They chuck out seeds like no-one’s business and you can grow them by the bucketful in a fairly modest patch of ground. Many of them are so committed to bursting into life that once you have let one flower in our garden, you will have it forever. Borage is like this. As is Nigella.
But is there so much pleasure in a prize so easily won? Once you have mastered the quick and the easy, your eyes might stray to the more elegant and the more enduring.
To perennials.
Perennial just means they keep going. Some die back over the winter, some plants just stay there, being wonderful, all year around.
Rudbeckia triloba
Why sow & grow perennials:
Oh so many reasons…
Perennials are expensive to buy. Even bare-root, even in small numbers, they do start to get expensive, and growing them from seed can get you a lot of bang for your buck.
Plants that keep living roots in the soil all year round are wonderful for biodiversity, for soil health and for keeping the microbiome under the surface, where it likes it best.
Soil exposure can be as damaging as disturbance. Even if you do a super-quick turnaround between the end of the annuals in summer and the autumn-sown for next year, there will be periods where the plants or small or the beds are empty. Perennials will cover the ground, reducing soil erosion, stopping water run-off, and meaning you have to weed less. With the changing climate, we are all going to need tougher, more heat-tolerant plants.
Conversely, if we have colder, wetter winters, perennials take away the guesswork about putting plants out in spring. I play chicken with the first frost when I am hardening my precious spring-sown annual seedlings. Perennials know better than me and they’ll come up when they are ready.
Did you hear me mention water? Even if you have a borehole (which I don’t) or a clever network of rainwater harvesting butts, watering takes time. Annuals are thirsty plants because they grow fast and flower hard. Perennials have longer to grow wonderful big, deep root systems, often communicating with and supporting the community of plants around them. They can access water and nutrients that annuals can only dream of, and the networks of roots improves soil structure and breaks up clay.
They are a very efficient use of your time, your efforts and general resources. Growing annuals means digging out and washing the pots or seed trays (oh ok, I don’t wash them, but I give them a bit of a wipe and a shake), driving to the local nursery or garden centre and buying some compost. Even peat-free, it’s got a footprint. Perennials, you do all that starting off once and you’ll get flowers for the foreseeable.
You get the gist? So why don’t we all grow them all the time? Because there are things that make annuals quite seductively attractive. They are the flash brass of the flower world. All fur coat and no knickers. I cannot pretend that you won’t get a bumper harvest out of a patch of annuals. You can successionally sow and get a whole summer of flowers. You cannot fool a perennial with light and heat to bloom at the time of your choosing, but annuals are easily led.
Aquilegia
And perennials are distinctly trickier to get started from seed. For me, perennials come into three categories.
Which ones are worth it?
Firstly, the easy. Easy as annuals but with so much more return for your investment. So, you can sow these just as you would an annual and either direct sow (risky but low effort) or start in trays and pots under glass.
The easy ones include: Aquilegia, Rudbeckia, Tweedia, Achillea, Alceas (Hollyhocks), Catananche caerulea var. Alba (White Cupid's Dart), Malva (new to me this year, the mallow) perennial foxgloves, Echinops, Eryngium, Gaura, perennial scabious, Verbena.
Hints that these might be relatively easy are that they are marked as ‘first year flowering perennials’. Chiltern Seeds has a fabulous website where you can select all sorts of filters, the most useful being ‘Good for Cutting’ (yes please) and ‘Life Cycle’ which means you can filter out perennials and annuals.
The trickier. They need a bit more fiddly stuff, a bit longer in the pots, a bit more specialist over-wintering or warming. You have to concentrate and put some effort in but they repay it in spades, and you will have more plants than you could ever afford to buy.
Includes: Campanula, Clematis, Delphinium, Echinacea (some people might disagree), Salvias.
Thirdly, the absolutely don’t bother. There are some people who will bother, and if that is you, all power to your elbow. You crack on. But I am never going to try and grow a peony from seed. The seeds take months to germinate and the plants then take years to flower. Ditto trees from seed. And asparagus. Just suck it up and pay for bare roots. Or bulbs. There are lots of places selling seed for Alliums. Life is too short.
I write off the third category, ordered my penies bare root and propagated my shrubs with cuttings. This just leaves the easy and the slightly trickier.
Seeds in both of the first two categories have been doing marvellously well with the bag method this February; I am astonished at how successful it is. My only complaint is that the name for the method sounds awful. Everything else about this method is wonderful. Why? because:
You can keep an eye on the seeds and control their moisture levels, light, and warmth just by shuffling some little bags around
You get to watch seeds burst into life. The psychological lift I get from this cannot be overstated
The germination rate is much higher than any other method, I think because compost and other growing mediums can be so much more variable. I have had to reduce the number of seeds I sow because in the first week of trying this method, I ended up with about a hundred Rudbeckia seedlings.
Perennials can be either slow to germinate or patchy in how many actually sprout, so if you are using pots and compost, you can have hundreds of them just sitting there with nothing happening. You can’t throw them away because you don’t know whether they will eventually come up, or if they have died a death. The natural flip side to the seed germination lift is the critical inner monologue that comes with being faced with a greenhouse full of pots and no living plants.
Please note, there are claims on the internet that even tiny seeds can be started like this. I found anything smaller than Campanula was really tricky and you run the risk of damaging the roots trying to remove the seeds from the kitchen paper. Unbelievably frustrating, even with tweezers.
How to do pre-sow sprouting
Fold some kitchen paper into a square that will fit into your ziploc bag. Slightly smaller than you think, wet kitchen paper is not easy to manipulate and it will be remarkably fiddly to get in and out once you have sprayed it with water. So much so that I recommend that you put the kitchen paper in the bag before you spray it.
If you haven’t got a spray bottle, I have tried dipping it in a very shallow dish of water but it is really difficult to control the level of moisture. You need it to be damp but not wringing wet.
Wriggle the paper into the ziplock bag. If it isn’t already wet, spray it a little.
Use a teaspoon to scatter a few of your seeds onto the paper. Only a few. I am so used to patchy germination that I scattered too many Rudbeckia in one and now I have a hundred seedlings that I don’t know what to do with.
Label with sticky tape. Put it somewhere warm. I use the edge of the lid of my cooker, but anywhere that is house heat will work.
Check them often. They want to sprout in the bag but they don’t want to grow there. As soon as you see a root, get onto the next step.
Pricking out
The pre-sprouting method will give you about a week, maybe ten days, to get your bits together. A few pots, peat-free compost and maybe some vermiculite.
I set up a couple of pots and removed any of the sprouted seeds on top of the compost, sprinkled with a little vermiculite, labelled and sprayed with the water bottle.
Put them on a light windowsill. On sunny days, I put them out in the courtyard to capture some of that solar energy directly. I put a lot of seeds in a single pot because I don’t have that many windowsills, and I will pot them up and turf them out to the greenhouse when they are big enough.
When to sprout
Usually, I preach the lesson of patience and prudence. Sowing too early is so often a problem for enthusiasts or for those of us who just can’t bear the months of darkness any more. For the fast growing annuals, this is reckless. You have to keep spring-sown annuals in pots in the greenhouse because the big wide world will overwhelm them (autumn-sown ones are generally tough as boots by then) but you run out of space, they outgrow their pots, get congested and cross.
Leave them until mid-March.
But I start my perennials in bags, on the cooker, in mid-February. They sprout and shoot, get potted on, wait for a bit, and then slowly unfurl into life. This is wonderful timing for those plants that have a longer fuse and a slower burn. The exception is Cobaea scandens. An annual but it takes its time.
Chilling makes a real difference (for some anyway)
It has taken an embarrassingly long time for me to catch on to the importance of pre--chilling seeds. Some plants won’t germinate, or will only germinate poorly or irregularly, unless their spring follows a prolonged period of cold weather. You can either do this by sowing them in autumn and hoping for a few good hard frosts, or you can fake it. This process is called stratification.
Seeds need moisture and cold, not just cold, so the fact that I keep my seeds dry in a fridge isn’t enough. The way to do it is simple though and fits seamlessly with the bag method above; a little ziplock bag, a damp square of kitchen paper, shake in the seeds and put it in the fridge.
I leave a fortnight for fridge chilling to be sure so it is worth getting organised in February for March sowing.
I swear by the freezer for Bells of Ireland though. They do really need a bit of mean treatment. About a week should do it. If you are feeling really mean, freeze the seeds in an ice cube tray and leave to melt on top of compost.
Aquilegia
Astrantia
Baptisia
Bells of Ireland
Campanula
Clematis
Delphinium & larkspur
Echinacea
Eryngium
Poppies
Phlox
Rudbeckia
Sanguisorba
Scabiosa
Thalictrum (meadow rue)
Viola
Remember to label very carefully indeed, especially if other people also use your fridge. And put a note in your diary when it is time to get them out.