Transplant outside
4–6 weeks before last frost
Permanent bed strongly preferred; deep taproot makes containers impractical and removal nearly impossible once established. Space plants 36 inches (90 cm) apart.
Crop guide · The borage family
How to grow Comfrey
A deep-rooted perennial herb grown primarily as a dynamic accumulator and high-nitrogen compost activator, with edible young leaves used cautiously in some traditions.
Symphytum officinale · also called common comfrey, knitbone
Partial sun
Beginner
Frost-hardy
Sun
Partial sun
Tolerates full sun where summers are mild
Frost
Hardy
Dies back to the crown in hard frost and re-emerges reliably in spring
Spacing
36 in
90 cm between plants
Sow depth
3 in
76 mm
To harvest
60–90 days
counted from transplant
Soil pH
6.0–7.5
slightly acidic to neutral
Timing
When to plant Comfrey
Windows are counted from the average date of your last spring frost.
Last frost
Transplant outside
4–6 weeks before
As soon as soil can be worked, 4–6 weeks before last frost.
First harvest
2–9 weeks after
60–90 days counted from transplant, so first pickings start around 2 weeks after the last frost.
−8
−6
−4
−2
0
+2
+4
+6
+8
+10
+12
Weeks relative to last spring frost
Fall planting:6–8 weeks before first hard frost to allow root establishment.
Background
Why grow Comfrey
Comfrey's roots reach 6 feet or more, drawing up minerals that shallower crops cannot access; the leaves break down rapidly into a potassium-rich liquid feed or compost activator. The cultivar 'Bocking 14' is sterile and will not self-seed invasively.
A little history. Native to Europe and western Asia; a tap-rooted perennial in the borage family. Even small root fragments regenerate, making eradication difficult — site selection is therefore permanent.
The season, step by step
From planting to harvest
Water and feed
All season
Water deeply once a week during dry spells; established plants are drought-tolerant. Water when the top 2 inches of soil feel dry and outer leaves begin to droop slightly. Aim for about 1 inch per week including rain.
Top-dress with compost once each spring; no further feeding needed in most soils. What to use: mature compost or well-rotted manure worked lightly into the surface.
Prune and maintain
As it grows
Cut all leaves to 2 inches above the crown up to 4 times per season; remove flower stalks promptly if using a seeding variety to prevent unwanted spread.
Harvest and store
60–90 days from transplant
It's ready when harvest when leaves are 12–18 inches long and fully expanded but before flower buds open; first-year plants should be cut only once to allow establishment. Wear gloves — leaf hairs irritate skin. Cut stems 2 inches above the crown with shears. Take outer leaves first; do not strip the plant bare in a single cut.
Use fresh immediately as a compost activator or liquid feed; leaves wilt within hours. For tea fertilizer, pack into a sealed bucket with water for 3–4 weeks.
Overwintering
No action needed in most climates. In the first winter after planting, apply a light mulch of straw over the crown to protect against repeated freeze-thaw cycles.
Companions
Good neighbours, bad neighbours
Plant it with
Apple
A ring of comfrey planted out at the drip line (the outer edge of the branches) makes a dense low cover that crowds out grass and holds soil moisture, and each cut of leaves can be laid straight down as mulch. Keep crowns 18 inches clear of the trunk.
Pear
Under a pear, comfrey often reduces the grass competition that slows young trees, shading the soil surface and keeping it damp between waterings. Cut it three or four times a season and leave the leaves where they fall rather than letting it flower and flop.
Potato
Gardeners have long lined potato trenches with wilted comfrey leaves at planting, on the belief that the potassium-rich foliage feeds the developing tubers as it breaks down. Keep the living clump well away from the row, since digging potatoes chops comfrey roots that then regrow.
Tomato
Comfrey's taproot works 6 feet down, well below the tomato's feeding zone, so a clump at the bed's edge takes little water or food from the crop. Cut leaves can then be used as mulch or steeped feed for heavy-fruiting plants.
Asparagus
Both are permanent plantings, so a comfrey clump at the end of an asparagus bed can stay put for years, shading soil and crowding out the grass that otherwise creeps into the crowns. Plant it outside the crown row, never among the spears.
Keep it away from
Tarragon
Comfrey's broad leaves and heavy clump can shade out and out-drink a slim tarragon plant, and its damp, rich preferences pull the bed toward the moisture that rots tarragon crowns. Site it at least 3 ft away.
Lingonberry
Comfrey's broad leaves and deep taproot out-muscle a 6-inch evergreen mat for both light and water within a season. Use its cut leaves as mulch by all means, but keep the plant itself out of the berry bed.
Crop rotation
After this crop
Rotation
A perennial — it holds its spot for years, so it sits outside the annual rotation.
Comfrey is a permanent perennial, so no rotation applies and there is no family gap to keep. It is a moderate feeder that mostly feeds itself from deep soil. Plan the site as a fixed feature of the garden, and use its cut leaves to build compost for the annual beds.
Trouble to watch for
Pests and diseases
Pests
Comfrey moth caterpillar
Sign
Irregular holes in leaves; small caterpillars visible on leaf undersides in early summer.
Fix
Hand-pick caterpillars; damage is rarely severe enough to warrant further action on a vigorous plant.
Slugs
Sign
Ragged holes in young leaves, silvery slime trails on and around the plant.
Fix
Set out beer traps or iron-phosphate bait around the crown; remove debris where slugs shelter.
Diseases
Comfrey rust
Sign
Orange-brown powdery pustules on leaf undersides; yellowing of affected tissue above.
Prevent
Remove and bin affected leaves promptly; improve air circulation by not overcrowding plants; do not compost infected material.
Crown rot
Sign
Soft, dark, foul-smelling tissue at the base of the plant; wilting despite adequate moisture.
Prevent
Plant in well-drained soil; avoid piling mulch directly against the crown; do not overwater.
Good to know:All parts contain pyrrolizidine alkaloids, which accumulate in the liver with repeated consumption. Internal use is not recommended; external or garden-utility use is the primary application. Consult current health guidance before any culinary use.
FAQ
Common questions about Comfrey
When should I plant Comfrey?
Spring: as soon as soil can be worked, 4–6 weeks before last frost. Fall: 6–8 weeks before first hard frost to allow root establishment.
How long until Comfrey is ready to harvest?
60–90 days, counted from transplant. It's ready when harvest when leaves are 12–18 inches long and fully expanded but before flower buds open; first-year plants should be cut only once to allow establishment.
Can I grow Comfrey in a container?
Permanent bed strongly preferred; deep taproot makes containers impractical and removal nearly impossible once established.
How often should I water Comfrey?
Water deeply once a week during dry spells; established plants are drought-tolerant. Water when the top 2 inches of soil feel dry and outer leaves begin to droop slightly.
Is any part of Comfrey unsafe to eat?
All parts contain pyrrolizidine alkaloids, which accumulate in the liver with repeated consumption. Internal use is not recommended; external or garden-utility use is the primary application. Consult current health guidance before any culinary use.
How should I store Comfrey after harvest?
Use fresh immediately as a compost activator or liquid feed; leaves wilt within hours. For tea fertilizer, pack into a sealed bucket with water for 3–4 weeks.
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