Clippings No.2 Potting dahlia tubers
Spring is THE time for potting-up bareroot summer-flowering bulbs and tubers. Today, I’m going to walk you through dahlias - the High Queen of high-summer bloomers! It’s very simple and very quick!
Today, we’re potting-up our delicious, delightful, dahlias! If you’re a dahlia newbie or you’re thinking about giving them a go for the first time, then please do! They are fabulous plants with a range of colours and forms that is simply mind-boggling. Whether you want subtle hues or a good’ol garish slap in the face, there’s a dahlia for you! So, what are waiting for? Go get some flower power!!
Step 1: Order quality
In the UK, there are specialist growers like Withypitts and Halls of Heddon. Then there are the prime retailers like Farmer Gracy, DutchGrown, Peter Nyssen and J Parkers. From experience, I’ve had excellent results from all of these. They’re not entirely faultless, but that’s just the nature of bulbs and bareroots.
When I’ve bought loose or pre-packed from garden centres and supermarkets (it’s the price… I’m only human… I can’t resist!), the results have been mostly underwhelming. Dahlias can live for many years and you can easily propagate from them, so if your budget allows, you’ll want to get the very best start.
Step 2: What will you need?
I plant bulbs and tubers in large batches, like a factory line. Everything is organised on the table or workbench and it takes me just 30secs to pot each tuber. A quick heads-up, after potting you’ll need a light, frost-free area to leave your potted tubers. More on that later… So, with your tubers safely delivered and awaiting your attention, there’s a few thing you need to get ready…
Clean plant pots and labels. I use 2-3ltr (2-3qt) recycled pots with lots of drainage holes. Tubers will arrive in varying sizes so it’s worthwhile having a few options to hand. The pot should be just larger than the tuber.
Peat-free multi-purpose compost. My go-to is always SylvaGrow. Choose a compost that is light, friable, and drains well. If you’re not sure, if it feels lumpy and claggy, add some perlite or grit and mix.
Trug or bucket. I like to use a large trug to unload the compost from the bag and bash out any lumps.
Gloves, a trowel, or a scoop if you don’t want to get your hands grubby.
Secateurs to snip out broken or soft tubers, old stems, or trim roots.
Hose or watering can to water your pots afterwards.
Step 3: Unpacking
Be gentle! Open the packaging and you will find a rather odd dangling collection of tubers, resembling peculiar potatoes! Treat them carefully as they can be fragile. Somewhere near the middle, you’ll see one or two old woody stems. Make a note of these.
Check over the tubers. The odd ‘tuber’ may come away in your hands, but don’t panic. It happens. If you find any that are soft or (sharp inhale) rotting, then cut these out before you go any further. If there is a mass of stringy roots, you can trim these off too. The tubers will produce new roots anyway.
Step 4: Potting
Scoop some compost into the pot, laying 1-2in or 3-5cm of compost in the base. Lightly firm this down. Now, very gently, lay the dahlia tuber in the pot, with those old woody stems pointing upwards. You can spread-out the tubers, but don’t force them as they’re likely to break off.
Now fill the pot with compost, jiggling the pot now and again, just to settle the compost around the tubers. You can push compost around the tubers with a finger, but I find a little jiggle is enough. Keep filling until the tubers are buried 1in or 2-3cm beneath the surface. Lastly, tamp down the pot on a hard surface. This should knock out any remaining air-pockets. Label the pot and set to one side while you pot up the rest.
Step 5: Watering
Here is where (I think) dahlia newbies may trip-up… simply by killing their dahlias with kindness. Once your tubers are potted-up, water the pots evenly and lightly! Your only aim here is to moisten the compost, not fill the pot with water. At this stage, we’re just rehydrating the tubers and roots. Right now, the tubers are not actively growing and drawing moisture. If you leave them in a pot of waterlogged compost, there’s a high risk of rotting the tubers.
Step 6: Protection
Dahlias are frost-tender plants. New shoots will be damaged or killed-off, if exposed to frost. So, once your tubers are potted-up, watered and left to drain, they need to go to a light, frost-free location like a greenhouse. I wouldn’t personally recommend a coldframe unless you can be absolutely certain it’s frost free and devoid of pests.
I don’t have a greenhouse, so I line them up on my north-facing conservatory windowsills. It’s well-lit and stays above 10℃. Keeping your tubers ‘under cover’ also helps protect those tasty new shoots from being gnawed off by… Yes! You guessed it! Our old friends, Slimey and Shelly. Slugs and snails LOVE dahlia shoots!
Step 7: Raising your dahlias
When you see new green shoots, give them another water and this time you can be a little more generous as the tubers and roots are actively drawing the moisture. From now on, regularly check moisture levels by either pushing a finger into the compost or by simply lifting the pot and gauging its weight. Ideally, you want to maintain a regular moisture level, rather than flood-n-drought.
Please don’t be tempted to plant them out just because they have a few leaves. Spring weather is unpredictable and infamous for its extremes. April and May can bring freezing temperatures and hard frosts, storms, hail, torrential rain… It’s far better to get them growing strongly under cover, so when they are planted out, they can grow away fast and survive any early attacks by the those dastardly marauding mollusks!
Happy planting! We’ll pick-up with dahlias again in a few weeks!
Practical guide (video)
Disclosure: This video was produced for DutchGrown™️ and I received payment for this work. They also supplied a range of dahlia tubers to trial and use in this video. They were excellent quality and sprouted within a a few days of potting.
Next up on the Clippings…
Caring for those spring bulbs! As spring progresses, I’ll be deadheading and feeding narcissus and tulips. After flowering, some will be lifted and planted out ‘in the green’. I’ll explain all next week!