I split my dahlia tubers and they're currently growing indoors in pots. I have 2 questions:

1. they're growing quite tall and spindly/thin. If I pinch out the top (never done before), how will it flower? Isn't the top stem where the flower comes from? i.e. if the tuber has 4 stems, and I pinch out all 4 stems - will it flower, i.e will it branch out?

2. I have 1 tuber which has only produced 1 stem and think this is all it will produce. Will this stay as 1 stem and therefore only produce the typical 3 flowers you see at the top of a stem?

This is the first year growing indoors, splitting and pinching. Normally I leave my tubers as big mounds and plant straight outside. I've always been cautious of over splitting as I like lots of flowers.

thank you

All of the dahlias growers that I know, divide their tubers every year, this will ultimately give you more flowers, because it gives you more plants.

Pinching the tops of the plants is standard practice. It is usually done after the 3rd or 4th pair of true leaves. Pinching encourages lateral branches to grow out, plus causes the top of the plant to fork. The laterals, and the two forked branches should all develop flowers. So pinching gives you a bushier plant with lots more flowers.

Another standard practice is to only allow one central stalk to grow from each tuber. This give you a stronger central stalk, which produces larger flowers. If you are not concerned about size then you can allow multiple stalks, but on the larger flowering types, it can make it difficult to stake the plant.

Myself - if the normal bloom size of the flower is 3-4" or less, I let multiple stalks grow, otherwise I snip off additional stalks.

Hope that helps.

The stem forking does make sense now.

I haven't got a light and would need to investigate options in the UK

Thanks again