Dahlias add so much beauty to the Summer garden with their diversity of colour, style and size. They are a perfect choice for both the garden and the cutting patch. Dahlias are an award winning garden plant and the RHS has given out 125 Dahlia cultivars the RHS Award of Garden Merit. We would not be without them here at Puriri Lane.
Originating from Central and South America between Mexico and Columbia, the dahlia is named after a Swedish botanist Andreas Dahl who lived from 1751 - 1789 and all of the fabulous varieties that we see today were developed from three namely dahlia coccinea, dahlia rosea and dahlia pinnata. The records at the Royal Horticultural Society show nearly 6,000 records (including species and cultivars) with new cultivars being bred all of the time.
WHEN & WHERE TO PLANT
Planting of Dahlia tubers depends on your location but you should be planting when the risk of frost has passed and soil temperatures are on the rise. We start our tubers in pots sometimes and then plant out as the weather improves and the ground warms up. Dahlias are a perfect choice for the home garden and actually their preferred conditions are morning sun and afternoon shade and can also be grown under shade cloth if you are wanting to grow them for a small scale cutting garden for flower sales. The whites particularly appreciate the shade. Plants will grow in most soils but we like to add a good amount of animal manure to amend our soil in winter prior to planting our tubers out. Sheep and Cow manure is the best. Other animal manures such as poultry should be used very sparingly as they are very strong and can cause damage to developing root systems. EVen growing a green crop prior that is dug into the ground prior to planting is an excellent way of increasing organic matter into the soil. You can also use general purpose fertilises as they too will give good results. Use this two weeks prior to planting and then apply a side dressing to plants as the first buds start to appear.
Dahlias need a balance of Nitrogen, Potassium and Phosphorous. Be sure not to add too much nitrogen to your soil as this will result it too much growth and not enough flowers. This will also impact the keeping quality of your tubers for the following season when you lift them at the end of Autumn. An NPK of 8-4-8 or close to will grow great Dahlias - if you grow great Tomatoes then you can grow great Dahlias! We use a seaweed based product which assists with strong root development.
The serious growers will also apply small amounts of Sulphate of Potash and Sulphate of Iron which promotes strong growth, better stems, and lots of vibrant coloured flowers as well as more of them.
GENERAL TIPS & TRICKS
Dahlias actually grow very well from cuttings and many think that you actually get a better and healthier plant.
Some people worry if they receive a small tuber rather than a large one but it is actually better to be smaller as smaller tubers will develop their root system a lot more quickly than larger ones
PLANTING YOUR TUBER
Some plants will need staking so put your stakes in first. Tubers should be place horizontally in the ground with the eyes of the tuber approximately 50mm from the stake.
Do not put fertiliser in the hole - remember to amend your soil before planting as mentioned previously. If you get a lot of rain where you live it is best to plant into a raised or mounded bed to avoid your tubers rotting. We use weedmat to help with this.
People often ask can we plant dahlias with other garden plants and the answer is absolutely you can, but be aware if you are planting them with roses but you will need to add extra fertiliser or you will end up with poor roses and poor dahlias as they will be competing with one another for food. It is also not ideal to plant them too close to big shrubs and trees about a metre from them should be fine as again it is all about making sure your dahlia does not have too much competition from other big plants. Also make sure that they will get enough sun but also a bit of respite from the hot afternoon sun.
When watering Dahlias actually are a lot more drought tolerant than what was previously thought but watering regularly does help. We water our Dahlias in the late afternoon as this gives the plants all night to recover. Watering earlier in the day can mean that the sun can burn the droplets of water on the leaves and the buds. Mulching is also excellent for keeping both weeds at bay and also helping to hold that moisture in the soil.
PRUNING OF DAHLIAS
Dahlias definitely need pruning to produce a productive plant and once your dahlia has produced its first 4 to 5 sets of leaves use some snips to take out the central tip which stimulates the plant to send up lateral stems from the sides which will give you a more compact plant and this also helps to produce more flowers
PICKING YOUR DAHLIAS
The best time to harvest your flowers is in the early morning when the flowers are fresh and as you pick be sure to have a bucket of water at hand and put them straight into water to keep them hydrated. Cut your stems at an angle and not straight across so that when they sit in a vase it means that the can take up water otherwise the stems sit flat on the bottom and the water cannot flow easily up the stem which will reduce their vase life. Add a couple of drops of bleach to the water in your case - the stems do not need to be crushed or scalded with hot water!
TO LIFT OR NOT TO LIFT
It is actually preferable to dig and lift your dahlia tubers at the end of the growing season and the reason for this is firstly if you live where you get a lot of winter rainfall there is a high likelihood that the tubers will rot in the ground. The other problem that occurs is that you may get a smaller plant with poorer quality flowers due to a clustering of shoots appearing. You can leave them in for a minimum of one year but they really should be lifted and divided.
DIVIDING YOUR TUBERS
Again you can opt to not divide, but dividing your tubers means you are reducing the chances of rot setting in which means that you will lose your tuber. Wash the dirt off your tubers so that you can easily see what you are doing.
When dividing your clump these tips will help you be successful
Be sure to retain part of the old stalk which is where the eyes of the tuber are and be careful not to damage the neck. They also recommend that you leave some of the tail on but you can reduce its length. Write the name of your tuber on with a pen or tag them in some way so that you remember what the colour is as I have mixed them up so many times!
STORAGE OF YOUR TUBERS
They can be stored in a ten kilo polystyrene fruit box lined with newspaper with about 50mm of potting soil mixed with coarse sawdust. Place the tubers in the box with the eye end lined up along the edge of the box because when they shoot you lessen the chance of damage when removing the tubers for planting Then cover tubers including the eye end with another 50mm of the same medium. This reduces the chance of dehydration. Tubers should not dry out and are best to be kept JUST damp.
When selecting new cultivars or types to grow, be aware that some Dahlias grow better in some areas and not in other areas. Some Dahlias bloom early in the season and others bloom late in the season. Grow the ones that you love
Please note that the information provided here is of a general nature based on our own growing experience and we are still learning every year so it is intended as a general guide - we hope you find it helpful