Verbena (vervain): sowing, growing in a window box and in a bed

Garden verbena for window boxes and tall purpletop vervain for the border: sowing step by step, care, powdery mildew and overwintering.

In short: Verbena, or vervain, is a warmth-loving plant for sun. Trailing garden verbena is sown in February to March on a windowsill at 20–22 °C and goes outside after mid-May. Tall purpletop vervain (Verbena bonariensis) is a short-lived perennial that self-seeds. Both flower from June until the first frosts.

Latin name	Verbena, vervain family (Verbenaceae)
Sowing	February–March on a windowsill, 20–22 °C, germinates in 2–4 weeks
Planting out	after the last frosts, usually from mid-May
Spacing	garden verbena 25–30 cm, purpletop 40–50 cm
Height	garden 20–40 cm, purpletop 100–150 cm
Flowering	June–October

Everyone imagines something different by verbena. Some picture low cushions in a window box spilling over the edge in pink, purple or red, others tall wiry stems with purple heads above which butterflies spin in August. Both are verbena, but they are different species with different needs.

In this article you will find which species suits where, how to sow them (one of them is a little tricky) and what to do so that verbena flowers until autumn and is not buried in powdery mildew.

Which species of verbena are grown here

The genus Verbena has around 150 species, mostly from the Americas. In gardens you will meet mainly four. Lemon verbena from herb beds does not belong to this genus; it is the shrub Aloysia citrodora with different needs.

Species	Height	Type	Where it suits
garden verbena (Verbena × hybrida)	20–40 cm	annual	window boxes, hanging containers, bed edging
purpletop vervain, Brazilian vervain (Verbena bonariensis)	100–150 cm, exceptionally more	short-lived perennial, often grown as an annual	middle and back of a bed, prairie-style plantings
slender vervain (Verbena rigida)	30–60 cm	perennial, in colder regions as an annual	dry sunny beds, edges
common vervain (Verbena officinalis)	30–70 cm	native wild perennial	naturalistic and herb gardens

For balconies and window boxes garden verbena is the one. It was created by crossing South American species, has flat clusters of tiny flowers, often with a white eye, and trailing or semi-upright stems. Purpletop vervain is its exact opposite: almost leafless, sparse, but tall and airy. You can "thread" it between other perennials, because it shades nothing.

Sowing verbena step by step

Verbenas grow slowly, so they are raised under cover. Roughly 12 to 14 weeks pass from sowing to the first flowers. If you want a flowering window box at the end of May, sow by the first half of March at the latest.

Timing. Sow garden verbena from February to mid-March, purpletop in March to April.
Compost. Use fine seed compost and moisten it only slightly. Verbena does not tolerate wet during germination; seeds in an overwatered compost go mouldy and rot.
Sowing. Cover garden verbena seeds with about 2–3 mm of compost, as they germinate better in the dark. Purpletop seeds only need pressing in and dusting lightly.
Temperature. Keep at 20–22 °C. Germination is uneven and takes 2–4 weeks, so do not throw the tray out after the first week.
Cold phase for purpletop. If purpletop seeds do not come up, put the sown tray in a bag in the fridge for 3–4 weeks and then back into the warmth. This cold shock markedly evens out germination.
Pricking out. When the seedlings have 2–3 true leaves, transplant them one at a time into cell trays or pots 6–8 cm in diameter.
Pinching out. With garden verbena pinch out the tip as soon as the plant has 4–5 pairs of leaves. It branches and forms a denser cushion.
Hardening off and planting out. From the beginning of May take the plants outside during the day, and after mid-May plant them out permanently.

You will find ready seed of garden verbena in a colour mix with us as Verbena – mix (Verbena × hybrida). Other dates for starting flowers on a windowsill are summarised in the article what to sow in February.

Position, watering and feeding

All verbenas want full sun, ideally at least six hours a day. In partial shade they flower less and powdery mildew attacks them more easily. The soil should be well-drained; in containers it helps to add a handful of perlite or fine gravel to the compost.

Verbena in a window box

3–4 plants are enough for a window box 60 cm long. It combines well with petunias, marigolds or ornamental grasses.
Water when the top layer of compost is dry. In July that is daily, on cooler days once every two to three days. Standing water in the saucer harms the roots.
From June add a liquid fertiliser for flowering balcony plants to the water once a week to once every 14 days. An overfed verbena grows into leaves and flowers less.
Water at the roots, not on the leaves. Wet leaves in the evening are the most common route to powdery mildew.

A self-watering window box with a reservoir saves a lot of work in summer, but even in that the compost must not be permanently soaked. For tips on other annuals that keep flowering all summer, see the article balcony plants that will flower until autumn.

Verbena in a bed

Purpletop and slender vervain are undemanding. They hardly need feeding and, once rooted, tolerate even longer drought. Purpletop stands on its own and needs no support, but in windy places you can plant it in groups of 5–7 plants, which prop each other up.

How to extend flowering until the frosts

With garden verbena the key is removing faded flower clusters. If the plant sets seed, flowering weakens. It is enough to go through the window box once a week and pinch off or snip off the dry heads with shears.

If the plants stretch and thin out in midsummer, shorten them by a third and feed them. Within two to three weeks they regrow and flower again. With purpletop vervain leave the faded heads if you want self-seeding for next year and food for birds. If you do not want seedlings, cut off the heads before they turn brown.

Powdery mildew and other problems

What you see	Cause	What to do
white floury coating on the leaves	powdery mildew, mainly in partial shade, with dryness at the roots and damp air	remove affected leaves, water at the roots, increase spacing; choose more resistant varieties next time
stretched stems, few flowers	too little light or too much nitrogen	move into the sun, shorten by a third, feed less
yellowing and wilting from the bottom	overwatering, root rot	let it dry out, check drainage from the container
fine pale speckling of the leaves, tiny webs	spider mites in heat and dryness	shower the plant, shade the container at midday in the heat
silvery spots, deformed flowers	thrips	remove affected flowers, use blue sticky traps

Seedlings that suddenly fall over at ground level after germinating have mostly been attacked by a fungal disease from overwatered compost. Repeat the sowing in clean compost and water only with a sprayer.

Overwintering verbena

Garden verbena does not survive the first light frosts. You can preserve a favourite colour with cuttings: in August cut 6–8 cm long non-flowering tips, remove the lower leaves and insert them in moist compost. Overwinter the rooted plants in a bright room at 5–10 °C and water only sparingly.

Purpletop vervain survives a mild winter outdoors, especially in well-drained soil. Do not cut it in autumn; the dry stems protect the base and the seeds. For winter put a layer of leaves or evergreen branches at its foot and cut the stems only in April, when new shoots appear. Even if the parent plant dies after a frosty winter, seedlings usually appear and just need thinning in spring. The general principles of preparing the garden for winter are summarised in the article important tips for preparing the garden for winter.

Frequently asked questions

Is verbena an annual or a perennial?

It depends on the species. Garden verbena (Verbena × hybrida) is grown here as an annual. Purpletop vervain and slender vervain are short-lived perennials that overwinter in a mild winter and well-drained soil and, in addition, self-seed.

When should I sow verbena?

Garden verbena from February to mid-March on a windowsill at 20–22 °C, purpletop in March to April. Direct sowing outdoors in May is possible only with purpletop vervain, which then starts to flower only at the end of summer.

Why is my verbena not germinating?

Most often because of overwatered compost or cold. Verbena germinates slowly and unevenly, over 2–4 weeks. With purpletop vervain, 3–4 weeks in damp conditions in the fridge and then a return to the warmth helps.

How long does verbena flower?

From June until the first frosts, as long as it has full sun and you regularly remove faded flower clusters. Purpletop vervain flowers from July to October.

Is verbena poisonous to dogs and cats?

Verbena is not on the list of poisonous plants of the American organisation ASPCA. Even so, do not let pets nibble the plants, and if an animal eats a larger amount and vomits, consult a vet.

Sources

Updated: 27 September 2026

Author: Jana Vránová, the editorial name of the Pěstík.cz team. She writes about the garden, herbs and essential oils. We take safety and dosage data from specialist literature and official sources, which we cite in every article.