How I grow Dahlias....
There are several ways in which you can grow Dahlias and every grower has their own particular way which suits them.
You can plant tubers in the open ground or you can propagate new plants from cuttings.
The way I grow my Dahlias is by propagation in the Spring.
Some growers would say that the new growing season begins the moment you dig up your tubers in the Autumn once the first frosts have blackened the lush green growth.
However, I would, for the purposes of starting the new growing season, begin from the moment I wake up the “sleeping” tubers from their winters rest!
I start my season in early to mid February. I start by taking my tubers and give them a thorough check over for signs of damage and decay. Once I am happy with them I place them in a tray with a layer of multi-purpose compost and apply a liberal amount around the fleshy tubers taking care to leave the crowns exposed. Once all the trays have been finished they are placed on my hot bed. The hot bed I use is a heat mat which is easy to install and maintain and gives a more accurate heat distribution than a soil warming cable. I then water them in well. This will encourage the fleshy tubers to really plump up and encourage the new growth to appear over the next few weeks. I set the temperature to around 55 degrees Fahrenheit.
(My Wife, Dawn, pays the Electric bill!!)
I keep a check on the tubers on a regular basis to see if there are any rotting tubers and to keep an eye out for signs of the new shoots just beginning to break through near the crown. This is where my new plants for the season are going to come from.
After two to three weeks you should see the tubers begin to spring into life. The tubers will begin to develop tiny hair like roots which can be seen by gently lifting the tuber to inspect the base. This is soon followed by the first signs of leafy growth around the crown. After around five to six weeks the first cuttings (leaf and stem) are usually ready. However, quite often the first cuttings are very thick and have a hollow stem. These cuttings are best to be disguarded as they are very difficult to root and do not produce such a good plant. It is best to wait for the next batch or even the third batch to take your cuttings as these will not have a hollow stem and will produce a more superior plant.
The new cuttings are ready to take when they reach approximately 3 to 4 inches high with two full sets of open leaves. I cut mine using a clean sharp knife just below the second open set of leaves. I then remove the lower set of leaves, dip the base of the cutting into rooting hormone powder and then plant in a cell tray of multi-purpose compost with added perlite which has been pre watered prior to planting. Once I have finished taking a batch of cuttings I place them on the hot bed.
I cover my cuttings with a layer of fleece suspended over the hot bed. This helps keep the warmth in and shades them from the sun, which can be very strong at this time of the year and can easily burn the young leaves. I then keep a close check on the cuttings daily and give them a gently spray with water as and when needed.
After two to three weeks the young cuttings begin to root and it is quite clear to see when this happens as the leaves stand proud and look full of life. A gently tug on the young leaves will confirm that a good root system has taken as the young cutting will stay firm in its cell.
At this stage it is time to move the cutting from its cell tray into a pot. I use a three and a half inch pot with the same growing medium and water well in. These are then put in a frost free greenhouse to continue to grow for two or three weeks. After this they are put in the cold frame to harden off prior to planting at the end of May beginning of June.
At the end of May to the beginning of June I plant my Dahlias. However, I have to prepare the ground in advance. Because my plot is very sandy I tend not to apply a generous quantity of well rotted farmyard manure until just a few weeks before planting. However, if my soil was on the heavy side I would apply it in the Autumn
I plant my plants out in double rows approximately eighteen inches apart with two feet between the rows. I then leave around four feet before the next double row.
Dahlia plants require support throughout the growing season as they can easily be damaged by strong winds. There are no right or wrong ways to support your plants. I used to use four foot canes with string tied around them, however, I now use plastic netting which is stretched over each double row supported by chestnut stakes at each end. This can be lifted up the posts according to how high the plant grows.
I give the plants a good watering in especially if it is dry at the time of planting and then give them up to two weeks before I start giving them some food.
I give them a high nitrogen feed on a weekly basis from the middle of June through to the end of July then switch to a balanced feed for the remainder of the season. Some growers switch to a high potash feed from the end of August but as yet I have not tried this.
Towards the end of June I start to pinch out the growing tips of my plants as it is takes around eight weeks from stopping to flowering for most of the varieties that I grow. I usually stagger this procedure over a week or two so that I don’t get all my flowers at the same time. Depending on what the variety is will depend how much of the growing tip I remove. If it is a large or giant variety I will usually leave just two or three pairs of leaves from the base of the plant. This will limit the amount of time it will take later on de branching the plant. If it is a medium variety I will leave maybe four to five pairs of leaves as this will allow eight to ten stems to branch out. Generally, the smaller the flowers the more breaks you allow to grow on.
It does seem a shame at the time to remove so much growth but after just a week or two you will see the difference with all the side shoots springing into life.
Once the plants start to put on an abundance of new growth the time to begin de branching begins. The idea behind this is to focus all the plants energy into producing a limited number of blooms which will improve the size and all round quality of the bloom. To achieve a show winning giant variety most growers will only grow two or three blooms per plant, three to five on a large, six to ten on a medium and eight to twelve on small flowered varieties. This depends on the variety and how it grows for you.
Towards the end of July and the beginning of August you will begin to see the first buds forming at the end of each stem. This is when the hard work really begins with the onset of disbudding. This involves removing the two side buds either side of the central main bud and usually at least the next set of side shoots below. This will improve the main flower and strengthen the stem. Again, depending on the variety, you may have to remove the side shoots further down the stem.
Throughout the season you may wish to spray your dahlias against insect attack and fungal infection. 2012 was a very wet season and for the first time ever my plants suffered from a fungal infection called Dahlia Smut. Having never suffered from any such infection before, I had not even considered spraying with fungicide as a preventative measure, but will do so in future. The disease appears to only affect the lower leaves causing white spots on the leaves that eventually turn black. Spraying with a fungicide appears to stop it from spreading but repeated spraying is required to prevent it from returning. The disease doesn’t appear to affect the tubers or the following years cuttings so there is no need to destroy affected plants. The disease doesn’t appear to affect the flowers either but does effect the quality of the foliage.
Then comes the yearly battle with the Dahlias worst enemy, the Earwig!
There are a number of ways to try and prevent damage to your prize winning blooms. These range from spraying with insecticide to filling flower pots with straw and turning upside down on a garden cane. My method of choice is to apply a generous amount of petroleum jelly to each stem near to the bud which I rub up the stem for about four inches or ten centimetres in new money! The little critters seem to dislike the sticky barrier although one word of advice would be to stick with the more expensive brand of petroleum jelly and not a cheap alternative as I found out to my cost this year that the cheaper one doesn’t work quite so well. I would name the preferred brand but they haven’t agreed to sponsor me yet!!!
By the middle of August you should start to see the first signs of colour from your plants and from now on you will be enjoying some wonderful colourful blooms up until the first frosts blacken the plants and the whole process starts again ready for next year.