Dahlia Growing Guide
Before we proceed, I must issue a warning. Growing dahlias is addictive and I mean really addictive. So think very hard before you make the decision to grow them because you will be embarking on an all consuming journey that you can never turn back from. But let's face it, who can say no to those layers of petals? For such a knockout bloom, they really aren’t difficult to grow. Just tick a few boxes and you will be solidly on your way to blooming success.
When To Plant
Planting time depends on your location. If you are in a warm, frost free climate, you can plant from September (even earlier in some locations).
If you are in an area that gets frost, it is best to wait until all risk has passed as Dahlias are frost sensitive. In these kind of locations, a general rule of thumb is a couple of weeks before or after Melbourne Cup Day (1st November).
As always, it is important to know your climate and plant accordingly in order to have success.
Dahlias like a good amount of sun. Their ideal scenario is mostly sun and some afternoon shade. However, I grow mine in a full sun position and provide a little shade when we are experiencing a heatwave and they do fine.
Finding a spot that has protection from wind can be beneficial as most Dahlias do grow quite tall and can be damaged by intense wind.
Drainage is very important, particularly when planting tubers out directly as the tubers rot easily in those early stages, so pick somewhere with free draining soil to eliminate this issue.
Dahlias like a well-draining, nutrient rich soil. I like to add aged sheep manure and compost to my soil prior to planting to give an extra boost (you can use cow manure if you prefer). It is best to prepare the soil a few weeks before planting. Dahlias favour a slightly acidic soil. An optimum pH for Dahlias is between 6.5 -7.
A Dahlia tuber consists of an eye, neck, tuber and tail. For first time Dahlia growers it is important to know the structure of the tuber to assist with planting, in fact none of this will make sense to you unless you know where the eyes are located on the tuber so here is an image to help you!
Did you know?
Bigger isn't better when it comes to Dahlia tubers. If you have the choice between a large tuber and a small tuber - pick the small tuber. A small tuber will be quicker to develop it's root system than a large one. Large tubers have more stored energy to rely on and develop their root system much later. Once we move into Summer weather and scorching days, a plant with a well developed root system will be more resilient.
Most Dahlias will need staking for support (or another method of your choice). Prior to planting, put your stakes in the ground. If you stake your dahlias after planting, it can damage the tubers. Once you have chosen your location, plant tubers horizontal with the eye facing upwards, about 10cm deep. Plant the tuber about 5cm from the stake.
Tubers can be spaced anywhere from 45cm - 60cm away from each other. They may grow when planted closer together however giving them this much space allows the tuber to grow well and be dug up easily without disturbing neighbouring tubers.
Maintenance and Care
After planting your tuber, don't water. Tubers have energy stored inside them that will start off their growth. Once they are growing above the surface, you can start to water them but only water lightly until they reach around 15cm high. If you water consistently before this stage, your tubers may rot in the ground.
When your plants sprout, it can be a good idea to protect them with something as they seem to be favoured by slugs. Simply cut up a milk or juice bottle to create a cuff and put it around your plant so the slugs and other pests can't access them. As your plants grow, they will need support as previously mentioned. If you have chosen to stake them, as the Dahlias grow tall, tie them to the stake using budding tape or something with a little flex like a ripped up t-shirt or stocking.
When your Dahlias begin to flower you may want to feed them (I don't do this but it is common practice). A fertiliser specifically for flowering plants will work however just make sure whatever you use isn't high in nitrogen as this will grow the foliage rather than produce more blooms. It can also affect your tubers, so make sure to check this before applying anything.
How you water your Dahlias will depend greatly on your location/climate and the conditions during the season. Whatever happens, consistent watering is the key to good results. Always water at the base of the plants. I apply a layer of mulch to my plants to protect the soil and help with moisture retention.
Tip: Once your Dahlias are full size and producing blooms, strip the bottom 15cm of leaves. This will increase airflow reducing the chance of disease and encourage the plant to put its energy into blooms and top growth.
So how can you get the most from your plants? There are definitely things you can do!
Pinching your Dahlias is a great way to get more blooms. It feels so wrong at first and like you might be hurting your plant but don't fear, it will pay off! The principle is that you pinch the top of the centre stalk to encourage the plant to put out side shoots, resulting in more blooms overall as well as longer stems. I like to pinch my plants when they have four sets of true leaves. Identify the sprout above the four sets of leaves and simply pinch it off with your fingers. Once you have pinched, a few weeks down the track you will see two stems start to emerge from that spot rather than the one you pinched off. Pinching does normally delay flowering for a week or two however it is absolutely worth it in the long run as you will have stronger plants that produce more blooms for you to enjoy!
When your plants are in full bloom, cut your flowers! This will encourage more blooms. If you want to leave your blooms in the garden to enjoy, just make sure you cut all spent blooms off of the plants quickly. This will stimulate more flower production and honestly, who doesn't love having a giant vase of Dahlias in the house at all times during Summer!