How To Grow Dahlias
- Sun: Minimum 6 hours/day
- Water: 1 inch/week
- Staking: if 30 inches tall or more
For late blooming varieties, earlier blooms on others and delayed spring weather.
- in greenhouse, sun room, sunny window or under lights
- flower pots or seedling trays
- slightly damp potting soil
- water lightly, tubers rot easily
- heat (70F pref ) to promote growth
- Prefer rich, sandy, well drained soil. Will tolerate other soils that are not too wet.
- Use raised beds in wet or poorly drained areas
- Remove all weeds and roots
- Add manure, compost, decomposed leaves, etc.
- If using fertilizer, use low nitrogen for vegetables or flowers
- Soil ph, prefer between 6.5 and 7
- Plant when the lilacs bloom and the corn is planted
- 2 feet apart unless a dwarf variety, 2.5 feet for very tall varieties, 1.5 for dwarfs
- In holes 1 spade depth deep
- Put a stake, of suitable height for the grown plant, in the hole
- 1 tsp 6-8-6 in the bottom of the hole, cover with soil
- Tuber on its side. Eye/shoot close to the stake about 6 inches below the surface
- If it has a shoot, leave the top exposed and fill the hole in as it grows
- Very little water after planting, until growing well. Tubers rot easily.
- Protect against cut worms and slugs by placing a toilet paper roll, partially buried in the ground, around the shoot
Growing Your Dahlias
- 1 inch of water a week from rain or by deep root soaking with irrigation or soaker hose.
- Tie to stake every 12 inches or so
- Prefer cool roots, mulch late in June after earwigs have nested
- If using fertilizer, 1 heaping tsp of super triple phosphate 0-46-0 per plant every three weeks from when the plants are 12 inches tall until late August. Water in well. This gives strong roots and stems and lots of flower
- Late July add 1 Tablespoon of Muriate of Potash 0-0-50 every 3 weeks until the end of September. Potash builds big, strong tubers.
- Stops the upward growth of the main stem of the plant
- Creates a shorter, bushier plant
- Allows for more flower development
- Done when the plant has 4 sets/pairs of leaves
- Part leaves and snap off the centre growing stalk just above the 4th pair of leaves. You could use a knife or scissors if you wish
- Creates longer stems on flowers, better for cut flowers
- More energy per bloom so bigger blooms especially in the large and giant varieties
- Dahlias grow buds in groups of two or three
- When the buds are small but can be individually seen, pinch out the smaller side bud(s)
- For long stems you may need to take off one or two sets of leaf side shoots. Depends on the variety.
Pests and Diseases
- Strong, healthy plants can thrive in spite of some insect damage
- Soap and water sprays control most problem insects
- Clean cut broken stems to reduce the chance of bacterial infections
- Cut off rotten stems well below the infection so it doesn=t spread to the tubers
- Stunted, twisted plants, pale curled leaves- probably dahlia virus
- Dig and destroy, preferably burn. Do NOT compost
- Sterilize tools used.
- Spread by nematodes and sucking insects
- Some plants may be carriers
- After killing frost or 1st of October
- Tubers rot in cold, damp soil, even if not frosted on top
- Cut off top, 6 inches above ground
- Leave for a few days up to 1 week to allow eyes to set
- Tie label on stem
- Dig with a long-bladed spade 9 - 12 inches from the stem. Must be a complete circle with overlapping cuts to sever long roots
- Using the spade, lift the tuber clump
- Clean the worst of the earth off
- Wash clump and leave on its side to drain and dry for 24 hours, protect from frost.
- Split clump removing broken, rotten, diseased, old and eyeless tubers
- Leave to dry and scab over cuts for 24 hours
- Place in storage medium (vermiculite, shavings, peat, etc) and containers.
- Store cool (about 5C, 35 - 45F) and dark