Before we moved to our farm we grew dahlias in pots. Around 300 of them at our rental property. We’ve learnt a thing or two along the way and here are some things we can share from our experience.
The dahlias we grow and sell are different to the bedding type dahlias often sold in punnets at nurseries. As a cut flower farm we grow dahlias which produce much taller plants with longer stems suitable for cut flowers. Our advice here particularly relates to these.
CHOOSING A POT
The size of your container matters. We wouldn’t recommend anything smaller than a 30cm diametre pot. We have grown dahlias in small pots in the past and had to cut the pots off the clumps at the end of the season as we were unable to get the tubers out. It may be more preferable to grow in plastic pots that you aren’t too attached to in case you need to cut the clumps out of your pots.
Pots can be at risk of tipping over once the plant is tall. You can reduce the risk of this by half burying the pot in the ground if you have space. This means that the tubers will be contained in the pot but the roots can reach out into the surrounding soil to stabilise the plant and look for nutrients and moisture. The soil in the pots will also be at lower risk of drying out when buried.
CHOOSING A CULTIVAR
In our experience, some cultivars grow large or long tubers (e.g. Coorabell Moonglow, Glenmarc Devine and Florelie Baroness) and will require much larger pots (maybe 50-60cm diameter). Other cultivars grow consistently smaller sized tubers and will fit in smaller pots. Pompon dahlias generally have smaller tubers. Some pompon dahlias we grow on our farm include Moorplace, Pride of Place, Winkie Lambrusco, Florelie Hayley, Florelie Lemon Drop, Glenbank Honeycomb and Little Peaches. Some other cultivars which produce consistently smaller tubers are Florelie Boysenberry, Florelie Harmony, Florelie Chryssie, Florelie Cowrie and Florelie Angostura.
FERTILISER and WATER
If you’re growing dahlias in pots, you will need to ensure that you are providing them with everything they need as the roots are unable to go searching for nutrients in the soil. This is especially important for micronutrients. Many off-the-shelf fertilisers won’t include micronutrients as plants don’t need much and are generally able to find them in the soil. When growing in pots make sure you provide these micronutrients in your fertilising regime
You must monitor the moisture level in your pots carefully! Pots can dry out quickly as the soil heats up faster and the amount of soil exposed to the air is high in relation to the total volume of soil the plant has access to. It is best for the potting mix to have opportunity to dry down between watering to encourage the plants to develop a healthy and robust root system that fills the pot – then give them a good soak.
On hot days, check the pots for moisture morning and night and water accordingly. Some wilting on very hot days is completely normal. If you stick your finger in the soil and it still feels damp, there’s no need to add more moisture even if the plant is wilting.
Dahlias love sunny positions, so try to find a location where they will get sun for the majority of the day. Some late afternoon shade is fine and may even help your plants grow longer stems but too much shade can be detrimental to plant growth and flowering. They’ll also be more prone to fungal issues like powdery mildew as the leaves are likely to remain wetter for longer.
As with planting dahlias in the ground, dahlias in pots have a growing season in most parts of southern Australia from early November to late April. When planting in pots, it may be easier to protect dahlias from frost, so you could plant your dahlias earlier and keep the pots in a warm, sunny, frost-free place until the weather warms up sufficiently and risk of frost has passed.
Plant ONE single tuber per pot with the eye of the tuber as close to the center of the pot as possible. If the tuber you are planting is too large for the eyes to be in the center, find a bigger pot. This can be a sign that the cultivar grows large clumps. The eye(s) will ALWAYS be the center of the plant as it grows so it is important for stability of the pot to have them in the middle. This is where the stalk will grow.
If you can’t see where the eye is on your tuber, you can still plant it with the crown section in the middle and the tail end toward the edge of the pot. If you plant it on it’s side it will find the way up when it starts growing.
Make sure your potting mix is friable (easily crumbled in your hands), damp and also enriched with a small amount of fertilizer before planting. If you’d like to put any stakes in or around your pot to steady the plant, make sure you do this as soon as you plant your tuber to avoid damaging the growing plant.
You’ll need to tip out your tuber clump at the end of the season and divide it before the next season or the pot won’t be able to accommodate the next years growth.
We recommend dahlias grown in pots also be pinched to keep the center of gravity lower, provide a more stable plant and give more stems and flowers.
For more information on caring for your dahlia plants – including how to pinch, check out this blog post.
We hope you love adding dahlias to your collection and enjoy the colour and abundance they bring to summer!
Lorelie and Hannah