How to grow violas and best varieties

Huge numbers of pansies and violas for winter containers are sold every year to gardeners who love their colourful blooms. Summer-flowering perennial violas, on the other hand, are much less widely grown. Yet they’re a great choice for the summer and will earn their place in your garden with an incredibly long flowering period, delightful blooms and lovely scent, plus they will grow back year after year.

Which? Gardening magazine grew a range of popular varieties in the north and south of the UK to see which would give us the best display.

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Key facts

PLANT TYPE Herbaceous perennial

POSITION Full sun or part shade

SOIL Moist but well-drained and humus-rich

How to grow violas: month by month

Best viola varieties

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Full testing results for violas

USING THE TABLE OVERALL RATING The more stars the better. Rating ignores price and is based on: flower impact 20%; flower duration 15%; flower display 15%; shape of plants 15%; vigour and survival 15%; scent 10%; health 10%. Figures given are from the second year of the trial. Height and spread taken at peak flowering in north London in the second year of the trial.

How we test violas

1. We chose 21 different varieties, including the most widely sold and well-known varieties. We also included a few newer varieties. 
2. We grew five plants of each variety at the Which? Gardening magazine trial garden in Capel Manor, north London, where the weather is mild with moderate rainfall, and at Alnwick Gardens in Northumberland, which has similar rainfall to north London but is colder in winter and cooler in summer. 
3. We assessed all varieties over two years. In autumn of the first year, we cut the plants back to around 5-7cm to encourage fresh growth. We watered the plants at times during the hot, dry summer. 
4. They were assessed for: flowering duration, scent and how good the overall the display was; how well they grew over two years and whether they became straggly; and how susceptible they were to common viola problems.

Caring for your plants

Planting

Plant in sun or part shade into well-drained soil that doesn’t dry out in summer. Violas also grow well in pots filled with a Best Buy compost for containers mixed with Best Buy controlled-release feed.

Watering

Water them during any long dry spells of weather in summer to prevent the soil drying out. Water daily if growing in pots.

Deadheading

In July, straggly plants can be lightly trimmed with shears to take off the top 2-3cm of growth. In autumn, when flowering has finished, cut plants back to around 5cm high.

Feeding

Plants grown in reasonably fertile soil shouldn’t need feeding. In poor soil, feed with a general fertiliser in spring. Either add controlled-release fertiliser to containers at planting time or liquid feed fortnightly with a high-potash feed such as tomato food. 

Common growing problems

Slugs

Slugs target new growth in spring. Pick off any you find and use organic pellets containing ferric phosphate to keep them at bay.

Read more about slugs.

Aphids

Aphids often attack the early growth in spring. Check the base of the plants, where they tend to hide, and squash any that you see to prevent them getting established.

Read more about aphids.

Leaf spot

Fungal diseases causing black leaf spots and downy mildew are common on perennial violas. Remove affected leaves and stems if you see them. Fungicide sprays can help with leaf spots, but not downy mildew. Don’t replant violas where badly affected plants have been grown before.