Dahlia Growing Guide
The dahlia tuber anatomy.
The 3 very important components necessary for a dahlia tuber to be viable to grow those beautiful addictive flowers;
- Neck
- Tuber/Body
- Crown with Eye
Without one of these three, a dahlia tuber will not grow.
No eye = the tuber will grow roots, though it will not sprout/grow. This is otherwise known as a “blind” tuber.
Broken neck = will not grow
Tuber rotten all the through to the neck = will not grow. Please note it is possible for the tuber to be viable if the rotten part is completely cut away- leaving as much healthy tuber as possible.
Dahlia tuber varieties come in all different shapes and sizes.
- Little & big
- Short and round
- Long and skinny
There is no such thing as “too small” of a dahlia tuber.
If it has all three competents- it’s going to grow the same plant as a larger tuber, if not even better. I have found in my patch- “Bigger is NOT better” The largest tubers I have planted did not not multiply like those of smaller planted tubers, to the extent of the large tuber not making any new tubers, not a clump, just the “mother” tuber.
STORAGE
Dahlias should be stored in a dark, cool & ventilated area, away from risk from weather elements, especially frost & pests that may eat them. Monitor dahlia tubers frequently for rot, mould & dryness.
PREPARING THE SOIL
The ideal pH for dahlias is around 6.8 or between 6.5 and 7 (neutral). A higher or lower pH will lock up nutrients making it harder for the plant to thrive. It is easy to test your soil with pH testing kits.
To raise the pH (making the soil more alkaline) add dolomite lime. Gypsum also helps to break up some types of clay.
Lowering the pH of alkaline soils is more difficult. Alkaline soils have a higher buffering capacity that counteract changes in the pH. Often changes are not long-lasting so you need to keep an eye on this. The addition of sulphur will help and so will leaf litter, animal manure and most composts because they tend to be slightly acidic - but not mushroom compost which is alkaline.
Dahlias are very heavy feeders or otherwise known as “gross feeders” preparing the soil with lots of Composts and animal manures are excellent for getting organic matter into the soil to improve its structure and to feed microorganisms that help break down soil.
Cow, sheep and horse manures are all good but chicken manure is the richest source of nutrients. If you use raw manure, incorporate it well into the soil and allow 6-8 weeks for microorganisms to break it down so it can be readily used by the new dahlias.
A green crop can be grown specifically to add nutrients and humus to the soil. Nitrogen-fixing legumes such as peas, fava beans and lupins can be mixed with mustard seeds which help fumigate the soil preventing things like nematodes and fungal pathogens. Plant the crop in July.
Dig it in before the crop flowers, 4-6 weeks before planting. Best cut the green crop just below the topsoil surface with a hoe. Apply a light dressing of nitrogen fertiliser, compost or both and allow seven to ten days for the soil to rest before digging it in. If you favour the no/low dig approach, this can be done lightly without turning over the soil.
PLANTING
We plant in full sun here on our farm, but full sun with afternoon shade is ideal too. Too much shade & you won’t get flowers.
Plant once all chance of frost has passed. Plant the tuber flat/sideways, 10cm below the soil with eye facing up. Cover with soil. DO NOT WATER until the shoot breaks through the soil and is approximately 15cm, otherwise the tuber can rot. Stake at planting if required.
Dahlia tubers are spaced at 40cm
FEEDING
In our dahlia patch, we use Earthlife Garden Mate & feed our rows with Rocky Point blood & bone organic fertiliser pellets, homemade comfrey liquid fertiliser & poultry manure pellets. Once buds first to form, it is recommended to stop feeding high nitrogen fertilisers and increase potash for more blooms and strong stems. We liquid feed fortnightly alternating applications of a foliar spray to the dahlia plants of Plant of Health products- Bio-Trace, Neem, Silica & Potash & Triple boost. At the end of the season it is best to give dosages of Potash to help the tubers strengthen for storage/ dormancy.
PINCHING or STOPPING
Apart from feeding and watering to keep the plants healthy there are ways of grooming the plant to control the quality and quantity of the flowers it produces.
From February most dahlias will be producing prolifically. Harvest blooms and deadhead constantly to ensure that blooms maintain size and colour.
GROWING
Staking is recommended to help keep the plants upright especially when windy.
The exact watering regime used will depend on soil type, rainfall, temperature and the size of the plant.
Regular harvesting and deadheading will keep your dahlia producing flowers.
New shoots are very vulnerable to slugs and snails. There are also other signs to keep an eye out for that can cause problems, from pests eating them to viruses to earwigs, mites and mildew.
VIRUSES
It is almost certain that a patch of any size contains some plants infected with one of the six or more viruses identified so far that affect dahlias. The most common sign of virus infection is yellowing of the leaf veins, sometimes accompanied by distortion and stunting of the leaves and stems.
Viruses in Dahlia are: dahlia mosaic virus, dahlia common mosaic virus, cucumber mosaic virus, tomato spotted wilt virus, impatiens necrotic spot virus and tobacco streak virus.
When you work on your plants or divide tuber clumps you risk moving a virus from infected plants to clean plants unless you disinfect your tools between each plant. The cheapest and simplest method is to dip the tools in a 10% solution of household bleach in water.
An aggressive “if in doubt, throw it out” approach will significantly reduce the incidence of virus over time.
Controlling populations of insects, especially thrips, that are known transmitters of diseases between plants will help contain the virus problem.
HARVEST/ ENJOY!
Resources-
Joining your state dahlia society is a great way to connect to other dahlia lovers.
“The Winkie Way” is a fantastic in depth book to read.
