Last updated: · rebuilt in my own voice from the original post, with the deep-pot method I use now and the mistakes that taught me to stop using shallow trays.
Borage taught me that a big seed does not mean an easy transplant. My first packet went into a shallow tray because that was what I had on the windowsill. The seedlings came up fast, looked wonderful for a fortnight, and then stopped. When I tipped one out, the taproot had curled around the bottom of the cell like a watch spring. I planted it anyway. It sat in the bed for three weeks, doing nothing, then produced a single flower stem in late August while the direct-sown plants beside it were already covered in blue.
The next year I used deep pots and moved the seedlings out younger. The difference was not subtle. Same seed, same garden, same weather — sturdier plants, earlier flowers, less sulking. That is the whole method in one sentence, and the rest of this guide is the detail that makes it work.
Quick answerStart borage indoors 3–4 weeks before your last frost, one seed per deep cell, 1 cm (½ in) deep, at 18–21°C (65–70°F). Germination takes 7–14 days. Give the seedlings 12–16 hours of light, thin to one plant per cell, harden off for 7–10 days, and transplant while they are 10–15 cm (4–6 in) tall — before the taproot starts circling.
| At a glance | Details |
|---|---|
| When to sow | 3–4 weeks before the last frost |
| Pot depth | At least 10–12 cm (4–5 in); deep cells or tall pots |
| Seed depth | 1 cm (½ in) |
| Temperature | 18–21°C (65–70°F) |
| Germination | 7–14 days |
| Light | 12–16 hours a day under a grow light; turn daily on a sill |
| Thinning | At the first true leaves; snip, do not pull |
| Hardening off | 7–10 days, starting with 1–2 hours in shade |
| Plant out | After the last frost, at 10–15 cm (4–6 in) tall |
| Spacing | 30–45 cm (12–18 in) |
| Time to flower | About 8–10 weeks from sowing |
Why Start Borage Indoors at All?
Borage is one of the easiest plants to grow from seed outdoors. It germinates readily, grows fast, and often self-seeds so freely that you spend the following spring pulling it out of the path. If that is true, why bother with indoor sowing?
Because indoor sowing solves specific problems, not a general one. It is a tool for a short season, a cold wet spring, heavy slug pressure, or a garden where you want a small number of plants in exact places. It is not the default, and it is not automatically better.
The four reasons that justify it
Your season is short. Borage needs about eight to ten weeks from sowing to first flower. In a cold climate, three or four weeks of head start can mean flowers in June instead of August. The RHS describes borage as an annual reaching 50–70 cm, and an annual that starts late has less time to set seed before the frost.
Your spring is cold and wet. Seed sown into cold, waterlogged ground can rot before it sprouts. Indoors, you control the temperature and the moisture. That matters most in clay soil or a garden that sits wet until May.
Slugs and birds are winning. A young borage seedling is soft, tender and popular. Raising it indoors gets it past the stage where a single slug can erase a row.
You want it in a precise spot. Between tomatoes, at the edge of a pot, or in a bed where you want the flowers to spill over a path. Starting indoors lets you place a plant exactly where you want it instead of thinning a random patch.
When direct sowing wins
If your spring is mild, your soil drains, and you are happy with borage in a general flower patch, direct sowing is less work and usually gives stronger plants. Borage has a taproot, and every transplant is a small disturbance. The plants that stay put never have to recover from being moved.
I direct sow most of my borage now. I start a small batch indoors for the containers by the kitchen door and for the tomato bed, where I want the plants to flower early. The rest goes straight into the ground in May. If you want the full season sequence, my guide to growing borage from seed to harvest covers both routes.
A quick word on eating it
Borage leaves and flowers are traditional garnishes, but the plant contains pyrrolizidine alkaloids (PAs). NC State Extension rates borage as low-severity poisonous and notes that the toxins can damage the liver and lungs and are potentially carcinogenic. Use it as an occasional garnish, not a daily green. Avoid it during pregnancy or breastfeeding, and if you have liver disease. My complete guide to borage leaves covers the safety detail, and my list of medicinal plants explains why traditional use is not the same as proven medicine.
The Taproot Problem
Borage sends down a strong central root almost as soon as it germinates. The root is designed to find water deep in the soil, and it does not wait for permission. In a deep bed, that is an advantage. In a shallow seed tray, it is a problem.
What the root does underground
The first root grows straight down. If it meets the bottom of a cell, it turns and runs along it, then coils. By the time the seedling has two or three true leaves, the root may already have circled the cell two or three times. The plant looks fine above ground. Below ground, it is already root-bound.
That is why borage started in shallow trays often sulks after planting. The root cannot straighten out, the plant loses water faster than it can take it up, and the leaves go limp or yellow. Some plants recover. Some sit still for weeks. A few never settle at all.
Why shallow trays fail
A standard 6-cell tray is usually 5–6 cm deep. A borage taproot can fill that in ten days. A yogurt pot is better, but only if it is tall and has drainage holes. The old cell packs that garden centres use for bedding plants are the worst choice: wide, shallow and designed for fibrous roots, not taproots.
The fix is simple. Use a pot at least 10–12 cm (4–5 in) deep, sow one seed per pot, and transplant while the plant is still young. Do not wait for the roots to fill the pot. The ideal moment is when the seedling has three or four true leaves and the root has reached the bottom, but has not started to circle.
When to Start Borage Seeds Indoors
Three to four weeks before your average last frost is the window I use. Not six to eight weeks, which some seed packets suggest. Borage grows quickly, and a plant that has been sitting indoors for two months is usually leggy, root-bound and hard to settle.
The three-to-four-week window
Count back from your last frost date. If your last frost is around 15 May, sow indoors in the third or fourth week of April. If it is around 1 May, sow in early April. The exact date matters less than the principle: the seedling should be ready to go out just as the soil warms, not weeks before.
In a cold spring, wait for the soil to reach about 15°C (60°F) before planting out. Borage germinates best between 15 and 25°C (60–77°F), and cold soil stalls the plant even if the air is warm. The RHS growing guide calls borage easy in most garden soils and best on a sunny site, which is a useful reminder that it does not need cosseting.
Using your last frost date
Your local extension service or a frost-date lookup will give you an average last frost date. Treat it as a guide, not a guarantee. I have had frost ten days after the average date, and I have had a mild March that made everything bolt early. Watch the forecast, and keep fleece or a cloche handy for the first week after planting out.
If you garden in containers, you can start a little earlier and move the pots in and out. The plant will still need hardening off, but a pot is easier to protect than a bed. My guide to growing borage in containers covers the pot size and aftercare in detail.
What You Actually Need
You do not need a greenhouse, a heat mat, or a shelf full of equipment. You need a deep pot, a light seed mix, a warm room and a bright window or a simple grow light. Everything else is optional.
The short list
- Deep pots or deep cells. At least 10–12 cm (4–5 in) deep, with drainage holes. Tall yogurt pots, root trainers, or 9 cm square pots work well. One pot per seed.
- Seed-starting mix. A light, sterile mix that drains. Garden soil is too heavy and compacts in a small pot.
- Borage seed. Fresh seed from a reputable supplier. One packet is plenty.
- Light. A south-facing windowsill can work, but a simple LED grow light gives sturdier seedlings. Borage stretches badly in poor light.
- Labels and a pencil. Borage seedlings look like several weeds at the two-leaf stage. Label the pot.
- A mister or small watering can. Something gentle enough not to wash the seed out.
- Small scissors. For thinning. Snips are easier than fingers.
What you can skip
A heat mat is not necessary. Borage germinates at ordinary room temperature, and a warm windowsill is usually enough. A heated propagator can speed things up, but it also dries the mix faster and encourages leggy growth if the light is poor.
You can also skip the plastic dome once the seeds are up. A cover helps keep moisture in before germination, but leaving it on after the seedlings appear traps damp air and invites damping off. Remove it as soon as you see green.
Choosing and Reading Borage Seed
Borage seed is large, dark and easy to handle. It is also cheap, which means it is easy to buy badly. A packet from a bargain bin may be two or three years old, and old seed germinates slowly and unevenly.
Blue, white, or something else
Almost every packet is the common blue borage, Borago officinalis. The white form is sold as 'Alba' or 'Bianca'. Illinois Extension describes 'Bianca' as a compact, sturdier form with white flowers, good for pot culture. It is a better choice for a small patio pot; the blue is more vigorous and more generous with flowers.
Check the botanical name on the packet. Borago pygmaea is a different plant: a low, creeping perennial from Corsica and Sardinia, not the culinary annual. It is sold alongside borage in some catalogues, and it will not give you the big cucumber leaves.
The packet check
Look for a packing date or a "sow by" year. Fresh seed is the single biggest factor in even germination. Borage seed stays usable for two to three years in a cool, dry cupboard, but it declines after that. If the packet has no date, treat it as a gamble and sow a little thicker.
For a full breakdown of varieties, storage and saving your own seed, see my guide to choosing, sowing and saving borage seeds. Gardeners' World's plant profile also notes that the species self-seeds readily, which is worth knowing before you let a plant set seed beside a gravel path.
How to Sow Borage Seeds Indoors, Step by Step
This is the method I use now. It takes about twenty minutes for a dozen pots, and most of that is filling and labelling.
Step 1: Fill and dampen the pots
Fill each pot to about 1 cm below the rim with seed-starting mix. Tap the pot gently to settle the mix; do not press it down hard. Water it before sowing, either with a mister or by standing the pots in a tray of water for ten minutes. The mix should feel like a wrung-out sponge, not a puddle.
Step 2: Sow one seed per pot
Push one seed about 1 cm (½ in) deep and cover it with mix. One seed per pot is deliberate. Borage germinates well, and two plants in one deep pot will compete and tangle. If you are worried about a dud, sow two pots rather than two seeds in one.
Step 3: Warmth and moisture
Keep the pots at 18–21°C (65–70°F). A windowsill above a radiator is often close enough. Cover the pots loosely with a clear lid or plastic wrap to hold moisture, and check daily. Do not let the mix dry out, and do not leave it standing in water.
Step 4: First light
Remove the cover as soon as the first seedling appears. Move the pots into bright light immediately. A borage seedling that spends its first two days in dim light will already be stretching, and that stretch never fully corrects itself.
Label the pots before you sow, not after. It is astonishing how similar borage seedlings look to a dozen other things at the two-leaf stage.
Starting Borage Indoors
Light, Water and Air: Caring for Seedlings
Once the seedlings are up, borage asks for three things: strong light, even moisture and moving air. Get those right and the plants grow sturdy and stocky. Get them wrong and you get tall, pale, floppy seedlings that never make a good garden plant.
Light
Give borage 12–16 hours of light a day. Under a grow light, keep the tube or panel a few centimetres above the tops of the plants and raise it as they grow. On a windowsill, turn the pots a quarter turn every day so the stems do not lean into the glass. A south-facing window is the best sill; an east-facing one is second best; a north-facing one is not enough on its own.
If the seedlings are already tall and thin, move the light closer. The new growth will be sturdier, but the stretched stem will not shrink. You can bury the stem slightly when you transplant, which helps a little.
Water
Water from below when you can. Stand the pots in a shallow tray for a few minutes, then take them out and let them drain. This keeps the surface drier and reduces damping off. If you water from above, use a mister or a small can with a fine rose, and aim at the soil, not the leaves.
The mix should be moist, not soggy. A pot that stays wet for days is a pot that will grow mould and fungus gnats. A pot that dries out completely will stall the seedling. Check daily with a finger, and water when the top centimetre feels dry.
Air and food
A small fan on the lowest setting, or a window cracked open on a mild day, strengthens the stems and discourages mould. Do not blow cold air directly on the seedlings. Just keep the air moving.
Borage is not a hungry plant. A good seed-starting mix has enough nutrients for the first few weeks. If the leaves look pale after the true leaves appear, give a very dilute organic liquid feed. Too much nitrogen produces soft, leafy growth and fewer flowers.
Thinning Borage Seedlings
If you sowed one seed per pot and every seed came up, there is nothing to thin. If you sowed two, or if a clump came up from a pinch of seed, thin to one plant per pot. Borage is vigorous, and two seedlings in one pot will compete for water and light.
When to thin
Thin when the seedlings have their first set of true leaves. The seed leaves are smooth and oval; the true leaves are hairy and slightly wavy. At that stage the plants are strong enough to handle a snip, and the weakest one has already shown itself.
How to thin
Choose the sturdiest seedling: the one with the thickest stem and the best colour. Snip the others off at soil level with small scissors. Do not pull them out. Pulling disturbs the roots of the seedling you are keeping, and a disturbed taproot is exactly what borage dislikes.
Keep one plant per pot. If you want more plants, sow more pots, not more seeds per pot. A borage seedling that is crowded at the root will never be as good as one that had the pot to itself.
Hardening Off Borage Seedlings
Seedlings raised indoors have never felt wind, direct sun or a cold night. Moving them straight into the garden is a shock. The leaves can scorch, the stems can collapse, and the plant can sit still for a fortnight. Hardening off is the process of getting them used to outdoor life gradually.
The 7–10 day schedule
- Days 1–2: Put the pots outside in a sheltered, shaded spot for one to two hours, then bring them back in.
- Days 3–4: Leave them out for half the day, with gentle morning sun. Keep them out of strong midday sun.
- Days 5–7: Give them most of the day outside, with more sun each day. Bring them in at night.
- Days 8–10: Leave them out overnight if there is no frost forecast. Check the weather before you commit.
Bring the pots in if there is frost, strong wind or heavy rain. Water them more often than you did indoors; outdoor air and sun dry the mix quickly, especially in small pots.
What can go wrong
The common mistake is doing too much too fast. Two hours of full sun on the first day will scorch the leaves of a windowsill-grown seedling. A cold night can set them back for a week. If the leaves go white or papery, move the plants back into shade and give them a few days to recover before trying again.
Hardening off is also a good time to check for pests. Slugs and aphids find young plants quickly. Look under the leaves and around the rim of the pot before you plant out.
Transplanting Borage Without the Sulks
Transplant borage once the danger of frost has passed and the soil has warmed. The plant should be 10–15 cm (4–6 in) tall, with three or four sets of true leaves. If it is already root-bound, you have left it too long; plant it anyway, but expect a slower start.
When the plant is ready
Water the pot an hour before you plant. A damp root ball holds together better than a dry one. Choose a sunny spot with well-drained soil. Borage tolerates light shade, but it flowers best in full sun. If you are planting several, space them 30–45 cm (12–18 in) apart; they get bigger than the packet suggests.
Planting out
- Dig a hole a little wider than the pot and deep enough for the root to hang straight down.
- Handle the seedling by a leaf, not the stem, and slide it out gently. If the roots are circling, tease the outer ones loose with your fingers.
- Set the plant at the same depth it was growing in the pot. Firm the soil lightly around it, not hard.
- Water well, then add a thin layer of compost or straw mulch. Keep the mulch away from the stem.
- Shade the plant for a day or two if the sun is fierce. A piece of cardboard or a flowerpot on its side works.
Borage makes a good companion for tomatoes and strawberries because it brings pollinators into the bed at the right time. The old claim that it repels tomato pests is mostly anecdotal; the reliable benefit is the insects it feeds. It is also a useful source of leafy material for the compost heap; see my guide to borage as a green manure.
The first week
Keep the soil evenly moist for the first week or two. Do not drown it. A plant that wilts in the afternoon and recovers by evening is usually fine; a plant that stays wilted is not. If the leaves turn yellow and the stem feels soft, the plant is probably too wet. If the leaves are crisp and the soil is dry, water more deeply.
Transplanting Borage Seedlings
How to handle the taproot, set the depth and water in a young borage plant.
Prefer YouTube? Watch it there.
Common Problems and What They Mean
Most indoor borage problems come back to three things: temperature, moisture and light. The symptoms are usually easy to read once you know what to look for.
The seeds won't sprout
Old seed, a cold room, dry mix or seed buried too deep. Check the packet date, move the pots somewhere warmer, keep the mix evenly damp, and sow no deeper than 1 cm. Give them two weeks, and up to three in a cool room, before you give up.
Seedlings fall over at the soil line
This is damping off, a fungal problem that rots the stem base. It thrives in wet, cool, still air. Prevent it with clean pots, fresh mix, careful watering and good airflow. Once a seedling has collapsed, it cannot be saved. Remove it and let the surface dry slightly.
White fuzz on the soil surface
Usually a harmless mould that grows on mix that is too wet. Let the surface dry, increase airflow, and scrape off the fuzz if it bothers you. It is a sign to water less, not a reason to throw the seedlings out.
Seedlings are tall, thin and floppy
Too little light. Move the pots closer to the grow light or into a brighter window, and turn them daily. The stretched stem will not shrink, but the new growth will be sturdier. When you transplant, bury the stem a little deeper than it was in the pot.
Roots are circling the pot
The seedling has been indoors too long or the pot is too small. Transplant earlier next time, and use deeper pots. If the roots are only slightly circling, tease them loose before planting. If they are tightly coiled, the plant will take longer to settle.
Leaves look pale or yellow
Check watering first. Too much water is the most common cause, especially in a pot without good drainage. If the soil is fine and the plant is growing slowly, a very dilute organic feed can help. Do not feed a plant that is sitting wet and cold; fix the water first.
Borage Seeds and Seed-Starting Kit I Recommend
You need very little to start borage indoors: a deep pot, a light mix, fresh seed and a bright spot. These are the four things I would compare first. The links are affiliate links, and the full disclosure is at the end of the guide.
A starter kit with trays, biodegradable pots and labels. The cells are shallow, so use it for the first week and pot borage on into something deeper as soon as it germinates.
Keeps seedlings short and sturdy when winter and early-spring daylight is weak. Borage stretches badly without enough light.
Small snips are the kindest way to thin borage. Cut the extras at soil level instead of pulling them and disturbing the taproot.
A 1 lb bag gives you plenty of seed for several sowings through the season, or enough to share with a friend.
Frequently Asked Questions
Can you start borage seeds indoors?
Yes. Use deep pots with drainage, keep the mix warm and evenly moist, and transplant while the seedlings are young. Borage has a long taproot that dislikes disturbance, so deep cells and early planting out make the biggest difference.
How many weeks before the last frost should I start borage?
Three to four weeks before your average last frost date. Starting six to eight weeks ahead usually produces leggy, root-bound plants that sulk after planting out. In a short season, start at the four-week end of the window.
How long do borage seeds take to germinate?
Usually seven to fourteen days at 18–21°C (65–70°F). In a cool room they can take up to three weeks. Fresh seed, even moisture and a warm spot give the quickest, most even germination.
How deep should I plant borage seeds?
Sow 1 cm (½ in) deep and cover with seed-starting mix. Borage seed is large enough to handle individually, but it still needs darkness and moisture to germinate. Water gently so the seed is not washed out of the pot.
Why are my borage seedlings leggy?
Almost always too little light. Move them closer to a grow light or into a brighter window, turn them daily, and keep the room cool rather than warm. The stretched stem will not shrink, but new growth will be sturdier.
When can borage seedlings go outside?
After the last frost, once the soil has warmed and the seedlings have been hardened off for seven to ten days. Plant them out at 10–15 cm (4–6 in) tall, before the taproot starts circling the pot.
Final Thoughts
Starting borage indoors is not difficult, but it is unforgiving of the wrong pot. The plant wants to send a root straight down, and a shallow tray gives it nowhere to go. Use something deep, sow one seed per pot, give the seedling strong light, and move it out while it is still young. That is the method that finally worked for me.
The rest is patience. Borage does not need rich soil, a heat mat or a lot of fuss. It needs warmth to germinate, light to grow sturdy, and a soft landing in the garden. Do that, and you will have blue flowers, happy bees and more seedlings than you know what to do with next spring.
More Borage Guides
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