GrowSabzHow to grow larkspur in pots
Also called Delphinium, delphinium, rocket larkspur, knight's spur · Consolida ajacis
لارکسپر
- ☀️ Sunlight
- 6–8hours daily
- 💧 Water
- 0.8 Levery 3 days, 10 L pot
- 🌡️ Ideal temp
- 15–24°C
- 🪴 Min pot
- 10 L25 cm deep
- 🧺 Harvest
- 70–90days from sowing
- ⚖️ Yield
- 1 kgper 20 L pot
Larkspur keeps producing once it starts. First picking comes around day 70, and the plant then crops for roughly 45 more days — but only if you keep picking. Blooms left on the plant is a signal to stop making more.
Short answer
Grow larkspur in a 10 litre container at least 25 cm deep, watering about 700 ml per 10 litres of soil every 3 days, and keep temperatures between 15 and 24 °C. First harvest comes 70–90 days after sowing.
Where to plant it
What size pot does larkspur need?
10 litres and 25 cm deep is the realistic minimum for a single plant. Pick a container below to see what changes.
| Container | Minimum size | Depth | Notes |
|---|---|---|---|
| Pot | 10 L | 25 cm | Ensure good drainage to prevent root rot. |
| Grow bag | 10 L | 25 cm | Provides excellent aeration for roots. |
| Open ground | — | 30 cm | Prefers well-drained soil and full sun. |
| Raised bed | 20 L | 30 cm | Allows for better soil control and drainage. |
Watering
How often should you water larkspur?
Every 3 days through the growing season, at about 700 ml per 10 litres of soil — every 2 days in hot weather, every 4 days when it turns cool. Water in the early morning. Base of plant works best.
Too little water
- wilting
- stunted growth
- flower drop
Too much water
- yellowing leaves
- stem rot
- stunted growth
Avoid: overhead watering; soggy soil.
Climate
Can you grow larkspur where you live?
No hardiness zone needed — compare your actual temperatures against the plant's own limits.
| Ideal range | 15 – 24 °C |
|---|---|
| Survives | -5 – 30 °C |
| Germinates above | 10 °C — best at 18 °C, about 18 days |
| Flowers drop | above 28 °C, or below 5 °C |
| Sunlight | 6–10 hrs/day, best 8 |
| Frost | Medium sensitivity |
The flower-drop thresholds matter more than the survival ones. A plant can be perfectly alive at 30 °C and still give you nothing.
How cold is too cold for larkspur? Check your temperaturesEnter your night low and day high — see if it survives, and if it will cropTimeline
Larkspur growing stages, day by day
Click any stage to see what's happening. Durations shift with temperature — a warm season runs roughly a quarter faster than a cool one.
Feeding
Fertiliser schedule for larkspur
Feed on the interval below, changing what you give as the plant shifts from making leaves to making fruit.
| Stage | What to use | Per 10 L | Every |
|---|
How to prepare each feed
Common mistakes
Why larkspur fails, and how to avoid it
- A container that is too small
Below 10 litres the root run is too shallow. The plant grows, flowers late, and drops whatever it sets because it cannot support the crop.
- Watering too lightly
A daily splash wets the top few centimetres and nothing else. Larkspur wants about 700 ml per 10 litres of soil — one deep soak beats three shallow ones.
- Ignoring the flower-drop threshold
Above 28 °C, or below 5 °C, flowers fall before setting. The plant can look perfectly healthy and still give you nothing — shade it through the hottest hours.
- Planting it beside Fennel
Fennel is known to release allelopathic chemicals from its roots that can inhibit the growth of many nearby plants, including larkspur.
Companions
What to plant with larkspur
Good neighbours
Larkspur and roses are classic garden companions, sharing similar soil and sun requirements. Larkspur's tall, airy spires complement the bushier form of roses beautifully.
Peonies provide a lush, full base for the upright spires of larkspur, creating a stunning visual contrast. They also share similar growing conditions.
Calendula attracts beneficial insects like ladybugs and hoverflies, which prey on common pests like aphids, helping to protect larkspur.
Dill attracts predatory wasps and other beneficial insects that can help control aphid populations on larkspur.
Nasturtiums can act as a trap crop for aphids, drawing them away from more desirable plants like larkspur. They are also aesthetically pleasing.
Keep apart from
Fennel is known to release allelopathic chemicals from its roots that can inhibit the growth of many nearby plants, including larkspur.
Rue can have an inhibitory effect on the growth of some plants, and it's generally best to keep it separated from delicate flowering plants like larkspur.
Aggressive groundcovers can outcompete larkspur for water and nutrients, especially when larkspur is young, stunting its growth.
Mint is an extremely vigorous spreader and can quickly take over garden beds, suffocating less robust plants like larkspur.
Problems
Larkspur pests and diseases
Each lists the weather that brings it on, so you know when to start checking rather than reacting once it's established.
Aphids humidity any · temp 15-25
Small, soft-bodied insects that cluster on new growth and the undersides of leaves, sucking sap and causing distorted growth. Can transmit viruses.
Powdery Mildew humidity 50-70% · temp 20-27
White, powdery fungal spots appear mainly on the upper surface of leaves. Causes leaves to yellow, distort, and die off prematurely, especially in crowded conditions.
Fusarium Wilt humidity any · temp 20-30
A soil-borne fungal disease causing yellowing, wilting, and eventual death of the plant, often affecting one side first. Stems may show brown discoloration inside.
Slugs Snails humidity >70% · temp 10-20
These mollusks chew irregular holes in leaves, especially on young plants. Look for silvery slime trails.
Crown Rot humidity any · temp any
The base of the stem becomes soft, discolored, and rots, leading to plant collapse. Caused by overwatering or poor drainage, especially in heavy soils.
Leaf Miners humidity any · temp 18-28
Larvae tunnel within leaf tissue, creating winding, pale trails or 'mines'. Can reduce photosynthesis and weaken the plant.
Black Spot humidity >70% · temp 18-24
Dark, circular spots with fringed margins appear on leaves, often surrounded by yellowing tissue. Can lead to defoliation.
Harvest
When to harvest larkspur
First picking falls between day 70 and day 90, and the plant then keeps producing for about 45 days. Pick often — what you leave on the plant signals it to stop making more.
How to tell it's ready
- When 1/3 to 1/2 of the florets on the stem are open, and the lower flowers are fully developed.
How much to expect
Storing it: Place immediately in water in a cool location, out of direct sunlight. Change water daily for longer vase life.
Questions
Larkspur: common questions
How long does larkspur take to grow?
About 100 days from sowing to the first harvest, with picking usually starting between day 70 and day 90. It then keeps producing for roughly 45 more days. Warm weather pulls that forward; cool weather pushes it back.
What size pot does larkspur need?
At least 10 litres and 25 cm deep for one plant. A raised bed wants 20 litres of soil and 30 cm of depth.
How often should I water larkspur?
About 700 ml per 10 litres of soil, every 3 days in normal weather — every 2 days when it is hot and every 4 days when cool. Water in the early morning.
Why is my larkspur flowering but not fruiting?
Almost always pollination. Larkspur carries separate male and female flowers and needs pollen moved between them — without insects, nothing sets. Hand-pollinate in the morning with a male flower brushed against the centre of a female one.
What temperature does larkspur need?
It does best between 15 °C and 24 °C and survives from -5 °C to 30 °C. Seed needs soil above 10 °C to germinate, ideally around 18 °C.
Can I grow larkspur in winter?
It tolerates cold better than most, down to about -5 °C, so a sheltered spot or a cold frame will often carry it through.
How do I know when larkspur is ready to harvest?
When 1/3 to 1/2 of the florets on the stem are open, and the lower flowers are fully developed.. Once picked: place immediately in water in a cool location, out of direct sunlight. change water daily for longer vase life.