Dahlias originate from the mountains of Central America, where the Aztecs grew them for both food and ceremony. They were brought to Europe in the 1700s and bred into the kaleidoscopic range we know today. In Australia, dahlias have earned their spot as show-stoppers in the summer garden, adored for their variety and drama.
Sowing Calendar
Best Months to Plant – Dahlia
Climate Zone
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Cool/Mountain
✓
✓
✓
Temperate
✓
✓
✓
Arid
✓
✓
✓
Subtropical
✓
✓
✓
Tropical
✓
✓
✓
Cool/Mountain – Dahlia
Method
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Start in trays
✓
✓
✓
Plant out transplants
✓
✓
✓
Direct sow
✓
✓
✓
Temperate – Dahlia
Method
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Start in trays
✓
✓
✓
Plant out transplants
✓
✓
✓
Direct sow
✓
✓
✓
Arid – Dahlia
Method
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Start in trays
✓
✓
✓
Plant out transplants
✓
✓
✓
Direct sow
✓
✓
✓
Subtropical – Dahlia
Method
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Start in trays
✓
✓
✓
Plant out transplants
✓
✓
✓
Direct sow
✓
✓
✓
Tropical – Dahlia
Method
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Start in trays
✓
✓
✓
Plant out transplants
✓
✓
✓
Direct sow
✓
✓
✓
Where to Plant
Shady Spots & Herb Gardens
Shady Spots & Herb Gardens
• Areas receiving dappled or indirect sunlight, often near trees or buildings
• Best for shade-tolerant herbs like mint, parsley, or greens like spinach
• Helps prevent sun stress and conserves moisture
• Often used in cooler corners of the garden
In-Ground Garden Beds
In-Ground Garden Beds
• Traditional garden beds dug directly into the soil
• Suitable for deep-rooted crops and long-term plantings
• Offers natural soil ecology and drainage benefits
• Requires proper soil preparation and weed management
Containers & Pots
Containers & Pots
• Portable planting vessels suited for patios, balconies, and small areas
• Provide complete control over soil composition and drainage
• Great for herbs, greens, compact vegetables, or ornamental plants
• Allow plants to be moved to follow sun, shade, or seasonal conditions
Pre-treatment
None Identified
There are no pre treatments required for germination.
Sowing Method
Start in Trays
• Fill seed trays or punnets with quality seed-raising mix
• Sow seeds at the correct depth—refer to seed packet for guidance
• Place trays in a warm, sheltered location with good light
• Mist or bottom-water to avoid disturbing small seeds
• Transplant seedlings once they develop 2–4 true leaves
Direct Sow
• Sow seeds directly into prepared garden soil or outdoor containers
• Best for plants that dislike transplanting, such as root vegetables and beans
• Loosen soil and remove weeds before sowing
• Sow at the recommended depth and spacing, then water gently
• Keep the area moist until germination and thin seedlings if needed
Watering
Medium
• Benefits from regular watering, especially during active growth or flowering
• Soil should remain moist but not soggy—allow topsoil to dry slightly between waterings
• Ideal for most vegetables, herbs, and flowering annuals
• More frequent watering may be needed during hot or windy weather
• A layer of mulch can reduce water loss and improve consistency
Fertilisation
Frost
Frost Tolerant
These plants can tolerate light to moderate frosts and may survive through cooler seasons.
Maintenance and Harvesting
Dahlias require regular deadheading and removal of yellowing leaves. Support tall varieties with stakes, and water deeply but infrequently. After flowering, cut back and lift tubers for winter storage.
Pests and Diseases
Aphids
Aphids are tiny, soft-bodied insects that cluster on new growth and the undersides of leaves. They suck sap from plants, causing leaves to curl, yellow or become distorted. As they feed, they excrete sticky honeydew that encourages sooty mould, and colonies can build quickly in warm weather.
Start with organic controls: blast colonies off with a firm jet of water, encourage beneficial insects like ladybirds and lacewings, and spray neem oil or insecticidal soap to disrupt feeding. Keep plants well watered and avoid excess nitrogen that promotes soft growth. If pressure remains high, selective chemical sprays can be used sparingly, taking care to protect pollinators and beneficials.
Powdery mildew
Powdery mildew appears as a white, talc‑like coating on leaves and stems. It thrives in warm days, cool nights, and still air, and can weaken plants by reducing photosynthesis, leading to yellowing and early leaf drop.
Prune for airflow, avoid overhead watering, and remove badly affected foliage. Organic sprays such as milk solution, potassium bicarbonate, sulfur, or neem help suppress outbreaks. Chemical fungicides are effective when started early, but use sparingly to preserve beneficial organisms.
Two-spotted spider mites
Two‑spotted spider mites are tiny sap‑suckers that stipple leaves, causing a speckled, yellow look and fine webbing—worst in hot, dry conditions. Unchecked, plants can defoliate.
Increase humidity around plants, hose undersides of leaves, and release or encourage predatory mites. Neem and horticultural oils suppress populations organically. Miticides exist for heavy outbreaks; rotate actives to reduce resistance.
Thrips
Thrips are slender insects that rasp and suck plant tissues, leaving silvery streaks and distorted growth on leaves and flowers. They can also transmit plant viruses.
Use blue or yellow sticky traps to monitor and reduce numbers, weed around beds, and encourage beneficials like minute pirate bugs. Neem oil and insecticidal soap offer organic suppression. If needed, use registered insecticides and rotate modes of action to avoid resistance.
Slugs & snails
Slugs and snails chew irregular holes in foliage and fruit and can wipe out seedlings overnight, especially in damp, sheltered spots.
Remove hiding places, water in the morning, and use beer traps, boards, or shelters to concentrate and hand‑pick. Copper barriers can deter them. For baits, iron‑based pellets are the safest organic option; use metaldehyde baits cautiously due to risks to pets and wildlife.
Growing Tips
• Dahlia produces weak, short stems in shade; plant in full sun for strong blooms.
• Dahlia stems snap in wind; stake early and tie in as plants grow.
• Dahlia tubers rot in waterlogged soils; improve drainage and avoid over-watering.
