Let’s start by clarifying the slightly misleading headline to this post and, in the process, clear up some important questions about dahlia tubers and bulbs.
First, there is no difference between what people commonly call dahlia tubers and dahlia bulbs. The important point here is that the weird potato-like structures that give us beautiful dahlia flowers are properly called dahlia tubers, or tuberous roots – not dahlia bulbs.
In fact dahlia tubers are potato-like structures, because potatoes are themselves tubers – just edible ones.
And, it is by looking at the structure of the tubers that you can tell they are tubers, not bulbs.
Bulbs – like those of tulips, daffodils or crocuses – consist of layers of what are fundamentally modified leaf structures (called scales) that surround the embryonic stem and flowers.
Bulbs also have a flatter ‘bottom’ where roots attach (the ‘basal plate’). They go dormant in winter, having used their foliage and to take in and store the resources they need for growing the next year.
Typically, therefore, you can peel back the layers of a bulb (or cut one open) and see the structures inside.
Bulbs grow offsets, or mini-bulbs, that gradually increase in sized and thus creating expanding clumps of plants.
Tubers differ from bulbs in that they have no basal plate or scales. They are made of undifferentiated tissue. There are no layers or other obvious internal structures.
Tubers have multiple growing points, called eyes. It is from these that the dahlia stems grow.
Sometimes it is hard to tell whether a dahlia tuber has or will develop eyes, and which is the top or bottom. In that case, it’s best to plant the tuber on its side and see what happens.
Tubers don’t produce offsets but do get bigger each year, increasing the number of growing points.
In warmer climates where soil is not likely to get waterlogged, dahlia tubers can be left in the ground over winter. If you do this, cut the stems back to just above ground level and place a good layer of mulch over the soil around the stems.
Where temperatures are consistently below freezing or where soli may be waterlogged, it is best to lift your dahlia tubers at the end of the growing season and store them in a dry place.
Wait util the first frosts, because if you keep deadheading dahlias they will flower until then.
Then take a fork and loosen the soil around the plant, lifting it up as a whole. Clear away the loose soil from the tubers, taking care not to damage them.
Then, cut back the stems to about 6 inches. Turn the plant upside down and store them somewhere for a few days where the water can be allowed to drain our of the cut stems.
Once all the liquid has gone, brush away as much of the remaining soil as possible, brush with anti-fungal powder and store the tubers in a cool dry place. Use wooden crates or boxes, which allow air to flow around the tubers, so that they don’t rot.
If you take care of your dahlia tubers in this way, You can plant them out again in the spring, after the first frosts, and experience the beauty of these wonderful plants again for another year.
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