My dahlias have just arrived in the post and I’m excited to start potting them up. It's very, very easy to do.
I have a 3-litre pot and I find particularly with the bigger dahlia tubers you need a decent sized pot. I've got here a non-peat based potting compost and you can see what I mean about needing a bigger pot as the tubers can sometimes be a little wayward, so you need the space to fit them in.
I always think dahlia tubers remind me of a bunch of salami sausages hanging in a butchers or delicatessen.
To kick-start their growth, the dahlia tubers need to get in contact with moisture, because in Spring they want to start to grow, so you just tuck them in with the compost, one to a pot. It doesn’t matter if the central stem is off to the side, so long as there’s plenty of compost and the stem is at soil level. This is exactly how it would have been grown in the propagating fields and so you don’t need to bury them deeply. Then, just pop a label on the side which is particularly important for planting out if you have lots of different varieties. You may also want to date the label, but you don’t have to.
Next, I pop that pot onto the bed with the capillary matting, give it a water and leave it to grow. April is the main month so I’d expect to see this tuber sprouting within 2-3 weeks before I see shoots. If I plant them in March it could be six or seven weeks before I see any shoots.
If you don’t have a poly tunnel then a greenhouse would be perfect, or even a window ledge. Just remember to keep the pots moist, not dripping. It’s often a good idea to have the pots sitting on a tray of grit where they can absorb water when they want to and that acts just like the matting. They like a little light, a bit of warmth but even a cold shed is fine as long as you’ve got some top light, perhaps a potting shed and just keeping them frost-free – that’s the only thing.