January 2025: How I Grow My Dahlias

19th January 2025

Many people passing my allotment last year admired my dahlias. The most common comment was “How do you grow them like that?” Read on…..

In all kinds of weather, dahlias can be relied upon to produce an eye-catching feature in any garden. The dahlia is not fastidious as to the soil in which it grows, and blooms of high quality can be grown by any novice. 

A wide range of types of dahlia is available these days, ranging from bedding types which can be grown from seed and costing pence, and tubers in plastic bags or rooted cuttings available in stores and garden centres, to exhibition types from specialist dahlia nurseries or from dahlia societies plant sales.

Obtaining Stock

When first starting, and even subsequently, you can beg, borrow, or steal good stock from an experienced dahlia grower or order from a reputable dahlia nursery. 
I order my new stock from two excellent nurseries:
Halls of Heddon – https://hallsofheddon.com/
Farmer Gracey –   https://www.farmergracy.co.uk/

I can assure you the tubers/plants you purchase from either of the above nurseries will far exceed the quality of those sold in garden centres and shops.

I order ‘pot Tubers’ (small tubers grown the previous season in pots) which I set up to provide shoots which I take as cuttings (see above). You can also order rooted cuttings which can be potted on, then later planted out…

I also ‘set up’ my own tubers, dug up the previous autumn and stored, in March/April and take their shoots as cuttings.

‘Setting up’ is simply settling the tuber into a tray of damp compost and placing it somewhere warmish. It will send shoots up from the top of the tubers close to the bottom of the stem.

Preparing for planting

“I will say this only once”
Dahlias are greedy and thirsty plants but satisfying their needs provides a rich display of colour.
Although dahlias will grow well in any soil, they thrive best in rich soil with good drainage, and one way to achieve this is to raise the level of the soil by incorporating as much humus as possible. Even though dahlias benefit from copious amounts of water, they dislike standing water, and good drainage should be ensured. 

I grow my dahlias in raised beds. 
Dahlia roots will grow down to considerable depths in search of water, and it is helpful if the ground is well dug. I apply a good layer of well rotted manure or garden compost in trenches in the dahlia beds in autumn/winter followed by a dressing of a basal fertiliser incorporated into the soil at least two or three weeks before planting. 

An organic fertiliser is best, such as bone meal, or fish blood and bone, at the rate of three or four ounces to the square yard (two good handfuls) is adequate. 

Planting out should not be attempted until all risk of frost is over.  This will be early June in our area.  Plants should be well hardened off before planting out.

I start my tubers off indoors or in my greenhouse and when the new growth is visible, the tubers are divided into pieces, each with a growing shoot, OR I take cuttings by slicing the shoots off about ¼” away from the tuber, 4 new shoots will later appear at the point of cutting and then planted out in late May/early June.. 

Large and giant types will require to be three feet apart while small and miniature types will be happily accommodated two feet apart. Dwarf bedding types can be grown as close as one foot when they will require little staking. 

The Planting Operation   

Mark the planting positions with a 4’ cane.
Before planting, young plants should be watered well and then laid out alongside their appropriate canes.  A hole is taken out by the cane slightly larger than the root ball and the plant set in so that when filled in, the surface of the soil will form a depression around the stem. This is to ensure that any water which is applied can soak down to the roots and not run away. The plant should be tied to its cane and labelled.

Newly planted young plants are a great attraction to slugs and snails which can decimate a dahlia bed overnight.  It is essential to protect against slug damage at this point and it is advisable to give a precautionary spray with a systemic insecticide. 

Early Season Care   

Once the young plants have become established, they make rapid growth, and it is important that the new growth is securely tied. A common method of supporting rapidly growing dahlia plants is to insert two further canes at an angle to each plant and then tie twine around the three canes at intervals to form an inverted funnel which will hold the plants firmly despite the strongest winds.  An alternative method is to use wire or plastic netting with a six inch mesh tied horizontally to the canes about two feet above ground. The plants grow through the netting and are secure against the strongest winds. 

After planting water the beds and apply a mulch of garden compost, straw, grass clippings, etc.. 

IMPORTANT Plants should be sprayed every fortnight. 
My regime is weekly spraying alternately an insecticide and a fungicide. This routine works very well for me.

Earwigs are often said to be a problem with dahlias but I have yet to see one.

Dahlia Pest & Diseases 

When July comes, most dahlias will begin to flower. At this stage, the main growing point should be pinched out in order to encourage the growth of side shoots. This means that the first flowers will be removed, so that if early flowers are needed, the growing point should be removed earlier still. ‘Stopping’ the plant can be done in mid June if an early display is sought, but for a spread of flowering for exhibition, stopping can be spread over a matter of weeks. Most small and miniature types can be allowed to carry all the side shoots which the plant will produce, but larger cultivars will require the side shoots to be thinned out, and in the case of giants, no more than four side shoots should be kept. 

Flowering

No fertiliser treatment should be necessary through the flowering season. The main requirement of dahlias is an adequate water supply. During hot sunny periods, dahlias will transpire through their leaves enormous quantities of water. An overhead spray may revive flagging plants, but water is most effectively applied during the evening and night.  Unless the soil holds water well, a good soaking of the plants once a week may be necessary to keep the plants growing and flowering. A good soaking of the roots is more effective than an overhead spray and small amounts of water given more often. 

If a dahlia plant is left to its own devices, each flowering stem will terminate in a flowering bud, with generally two smaller buds alongside it. The two side buds, or wing buds should be pinched out as soon as practical. This will encourage the terminal bud to grow larger and develop a longer stem thus lifting the opening flower well above the foliage. The two side shoots below the terminal bud should also be removed to encourage the growth of the terminal flower and of the stem. If bigger and better blooms are required for show, then more side shoots lower down the stem can be removed. In the case of giants, all the side shoots can be removed, perhaps leaving the lowest to survive to produce a replacement flower later on in the season. 

Throughout the flowering period, those flowers past their best should be removed as with most flowering plants, ‘dead heading’ encourages new flowers to develop. The succession of flowers is helped if the plants are fed with a foliar feed and given adequate watering.  

Cutting blooms for the house or for show is best done either early morning or late evening. A sloping cut should be made and the blooms placed immediately in a container of cold water.  A long stem should be aimed for, so that when arranging the blooms there is plenty of stem length to show the blooms to their best advantage. 

Exhibiting

Most dahlia growers love to have dahlias in the garden and perhaps to cut some blooms for the house, but few actually intend putting dahlias in a flower show. Even so, all visitors to a flower show are envious of the exhibits with which they are confronted. Many people wonder whether they could in fact match such exhibits? The truth is that with a little effort, such exhibits are possible by a novice. 

In many small local horticultural shows, the requirements are not as stringent as in major specialist dahlia shows, and nothing will be lost in entering a few dahlias in the appropriate classes. Judges in all shows are looking for exhibits which match the requirements of the class, which are of good quality, and free from damage or blemishes. The rest comes from experience, and this will not be gained without entering and matching one’s exhibits with other competitors, so why not give it a go! 

Lifting and Storing Tubers 

Sooner or later each year a frost comes which blackens the dahlias, and the time has arrived when the dahlias have to be lifted. The major problem is storing these tubers over winter. 

In general, a cool temperature (2-3 degrees C) is ideal and a covering of dry peat or vermiculite will stop them drying out. 

Once the foliage is cut back after frost, the tubers should be lifted, and the surface moisture allowed to dry out.  Some growers then set the tubers up in boxes of peat in a cold greenhouse or cold frame until they start into growth in the spring. All that is needed is protection against frost, and regular inspection against rotting. In the following spring, tubers started into growth can be split into manageable pieces or cuttings taken in order to multiply selected cultivars for next season. 

  • Tip 1 – Do not wait until frost kills the stem before digging – dig once foliage has been killed by frost
  • 
Tip 2 – Store tubers under greenhouse bench directly with contact with soil either encased in soil (as dug) or washed
  • Tip 3 – Cover Dahlia tubers with either: fleece, old blankets or straw to stop frost
 

Did you know?

Dahlia tubers are edible!

Preparation: 

  • You can bake, boil, mash, or roast dahlia tubers.
  • Cook them until they are very soft.
  • You can use a cooler oven and a skewer to check for doneness.

Nutritional value:

  • Dahlia tubers are rich in vitamin B6, riboflavin, and potassium. 
  • They are also a source of inulin, a low calorie carbohydrate that can boost gut bacteria. 

History:

  • The Aztecs cultivated dahlia plants for their sweet, starchy tubers.
  • In some parts of the world, dahlia tubers may have been part of the human diet for thousands of years.

And No I haven’t tried eating them but I will when I take my tubers out of winter storage!

Preserving Stock 

Some cultivars do not make good tubers, others make tubers that are extremely large and take too much space on the propagating bench. It is a good idea to leave one or two plants of each cultivar in their pots, and allow them to grow in the pots (‘Pot Tubers’), which are planted in the ground. The plants will develop tubers inside the pots, and because they are restricted their size is more controlled. When the frost strikes, the pots should be dug and the tops trimmed off as with the other plants. The tubers are called pot tubers, and these are the best for propagating from the following season, and are the tubers normally sent out by nurserymen.

There it is, nothing difficult. I assure you it is easier in practice than it appears in words.
Have a look at the two websites above and get your orders in.

Meanwhile,
Keep Healthy, Keep Smiling, Keep Sowing.
Best Wishes,    
Ramon 07594 456292
Plot 21 Silsden Road site

February’s Factsheet No 5 is “Fertilisers Made Simple”