Dahlias are one of my favourite summer flowers, together with sunflowers and zinnias. Together, they make an incredibly attractive display and are a powerful magnet to attract bees and butterflies to the garden. Dahlias provide non-stop colour from December until even as late as May, when the first frosts start to set in. They are an excellent cut flower and last for a long time in a vase. Furthermore, they are excellent value as like all bulbs, the tuber will die down over winter and reflower in subsequent summers.
Dahlias can be grown from seed or tuber. I will cover both growing methods in this blog post.
Sowing dahlias from seed
Dahlias can be started from seed indoors in October or even earlier if you live in a more temperate zone and have a hot house to protect them from the cold. Dahlia seeds need warmth in order to germinate. I germinate seeds in punnets filled with seed raising mix from Gardn Gro. I like Gardn Gro’s seed raising mix as it is very fine in texture, enabling seeds to push through the mixture easily as they rise to the surface. I place the punnets inside plastic incubators which you can purchase from garden centres. I then place the incubators on a heat pad indoors and spray plants with water once daily or twice if the seed raising mixture is very dry. If you don’t have a heat pad you can also use your hot water cupboard which will also provide seedlings with a warm environment so they can germinate successfully.
Dahlia seed varieties
Most dahlia seed tends to be the bedding varieties, but it is possible to grow cactus and pompom varieties from seed too. Two popular dwarf bedding varieties are Dahlia Deco Dwarf Green Leaf Mix and Dahlia Diablo Dwarf Bronze Leaf Mix (both from Egmont Seeds).
To order seeds from the very extensive Egmont Seeds range, visit http://www.egmontseeds.co.nz/.
How to care for dahlia seedlings
For new gardeners, those who don’t wish to start their dahlia seedlings from seed or if you’ve simply left it too late, plants are available for sale in nurseries from October onwards. Palmers stock a great range of dahlia seedlings. Awapuni also sell high quality, large grade dahlia seedlings delivered direct to your door. Look out for Bedding, Figaro, Red Skinned Mixed and Tall Cactus Mixed varieties. If you order 7 or more bundles of seedlings, delivery is free.
I plan to sell dahlia seedlings in my own boutique nursery later in the season. Keep an eye out for details in my newsletter, on Neighbourly and my Facebook page as to when they become available. During October and November, I will also circulate updated lists of available stock in my plant nursery to subscribers of my free weekly gardening newsletter. To be added to my mailing list and receive these notifications, please email me at firstname.lastname@example.org.
Dahlias need at least 6 hours of sunshine per day, so be sure to plant seedlings in the sunniest spot in your garden. Before planting dahlia seedlings, take the time to prepare the bed properly so plants receive adequate nutrition. Dig the area over that you wish to plant your seedlings in. Mix plenty of compost and some sheep pellets into the ground. I highly recommend Gardn Gro’s Wonder Nuggets, which are 100% organic and function as an excellent fertiliser. Rake the ground so that it is nice and level. Be sure to water plants every day, preferably early in the morning or in the evening. Liquid feed dahlias weekly to encourage the growth of healthy leaves and the formation of flowers. Snails adore dahlia plants, especially when they are young, and can completely decapitate your seedlings. Protect young seedlings from snails by placing snail pellets around the plants.
Dahlia seedlings will form a tuber underground which means that they will grow again in future seasons. If you save seeds from your plants, note that they may not come true to type. This is not necessarily always a bad thing. Who knows, you might even breed a new and interesting variety!
Growing dahlias from tubers
It’s definitely easier to start your dahlias from tuber. If planted in the spring, tubers should flower prolifically in summer.
Palmers stocks a great range of dahlia tubers every spring. You can also order dahlia tubers direct to your door from NZ Bulbs, who stock some unusual varieties which can be hard to find in garden centres.
As with planting dahlia seedlings, take the time to prepare the ground well. Dig the area over that you wish to plant your tubers in. Mix plenty of compost and some sheep pellets into the ground. Dig a hole deep enough to bury the tuber, leaving any shoots above the surface. It’s a good idea to place a stake at the time of planting for support as your plants grow, to avoid injuring the tuber later on. If you are planting more than one dahlia, make sure you leave enough space between tubers. I recommend spacing dahlia tubers at least 1-1.5 m apart.
As shoots emerge, sprinkle a little sulphate of potash from Gardn Gro around your dahlias, to encourage healthy and plentiful flowers. Liquid feed dahlias weekly in spring to encourage strong, healthy growth and flowering in summer. From Labour Weekend onwards, water plants regularly, preferably early in the morning or in the evening.
Once your dahlias have finished flowering in autumn, the foliage will start to die down. Sprinkle a little bulb fertiliser around the base of your plants to nourish the tuber so it flourishes in future years. Dahlias can be left undisturbed underground for several years. It’s a good idea to divide your tubers every 4-5 years otherwise the clump will become very big, making it harder to break into pieces. When dividing your dahlias, make sure that each piece has an “eye” from which the shoots will emerge, otherwise the tuber will not grow. I advise not making the divisions too small. You can swap excess tubers with other gardeners to obtain different varieties or plant the extra tubers in different places in your garden.
Dahlia tuber varieties
Dahlia tuber varieties fall into several categories: Cactus (spiky flowers), Decorative (large flowers with round petals), Pom Pom (as the name suggests, pom pom shaped flowers) and Collarette (small daisy-like flowers which are incredibly attractive to bees).
There are so many dahlia varieties I wouldn’t know where to begin! One of my favourites is a bright yellow pom pom dahlia which came from a mixed bag of tubers I purchased from a garden centre many years ago.
In addition to the existing varieties in our garden, I am growing some new varieties this summer, including the following:
o Pink Silk
o Catching Fire
o Mom’s Special
o Blue Wish
o Crazy Love
o Hapet Blue Eyes
o Hy Trio
o Leila Savanna Rose
o My Love
I will follow up with a further blog post later in the season, reporting on the progress of these varieties in the garden.