When to Plant Dahlia Seeds: Timing it Right for Better Blooms

You’ve got your seeds, you’re ready to go, but when is the best time to start sowing them? 

Well, that's a topic of some debate. Although most experts agree the best time to start dahlia seeds is six to eight weeks before the final frost, in practice the timings can differ quite a lot - something you've probably noticed on Instagram and in dahlia forums. It means that, for a beginner, it can be quite hard to work out. So we’ve tried to cut through the noise and create a simple guide on when to plant dahlia seeds, including what we’ve found works best for us here in the south of England. 

When to plant dahlia seeds for beginners

If you want a less time intensive route to your blooms and if you have the patience to wait, then the start of April is a pretty safe bet for most in the UK. 

There will be enough natural light to avoid the need for grow lights and, with the last frost in May, you won’t have to do too much in the way of potting on before you can get them in the ground outside. 

So for most, April 1st is a good date to mark in your diary…but what we are not known for at The Untamed Garden, is patience.

When to plant dahlia seeds for the impatient (and those with time and grow lights) 

 If, like us, April 1st seems like a really long time to wait, you can go early. We should be clear up front that this is not a beginner route and not something you need to do. There are many gardeners who would advise against it and dispute that there are any gains to be made. It’s just what works for us. 

Bearing that in mind - we often get going towards the start of March (we have actually been known to sometimes go as early as the end of Feb - but don’t tell anyone!). Sowing this early means you will need a set of grow lights though, to prevent the plants going ‘leggy’. We find we’re able to get away with one set of lights that we move between the seedlings every couple of days.

You’ll also need to be prepared to do more work potting on, to keep them growing well until it’s safe to plant out - which is usually mid to late May in our part of the UK.

Dahlia seedlings benefit from having a grow light, when started early, to encourage strong plants with healthy roots.

Are there any benefits to sowing dahlia seeds early? 

To get earlier blooms it’s definitely worth sowing dahlia seeds by the start of April. Going earlier than that might mean you will have bigger seedlings to plant out, which may have a better chance of outrunning the slugs. You might also get earlier flowers - but there are no guarantees and you’ll need the time to really nurture them. If in doubt, we’d stick to April. 

How late can you plant dahlia seeds?

Found a pack of seeds you forgot to plant, or life got in the way of? It happens to us all. The good news is that you can probably keep sowing until around mid May and they should still produce tubers. After that, we’d store the seeds somewhere cool and dry and hold fire until next spring.  

Want to know more about how to grow dahlias from seed? Check out our guide here.