Best Autumn Flowers for a Greenhouse
Autumn is a magical time in the gardening calendar. The air turns crisp, leaves transform into fiery shades of amber and crimson, and many gardeners retreat indoors to prepare their greenhouses for the cooler months. For those lucky enough to own a glass greenhouse, autumn offers an opportunity to fill the space with a colourful tapestry of flowers that can thrive away from the harsh elements of the British autumn and winter.
In this comprehensive guide, we’ll explore the best autumn flowers to grow under glass in the UK, why a greenhouse extends your flowering season
Why Use a Greenhouse in Autumn?
Autumn in the UK can bring early frosts, heavy rain, and strong winds. A greenhouse creates a sheltered environment that:
- Extends the flowering season well into late autumn or even winter.
- Protects delicate blooms from damage by wind and rain.
- Provides more stable temperatures, reducing plant stress.
- Enables you to experiment with more tender species that wouldn’t otherwise survive outdoors.
Top Autumn Flowers for Greenhouse Growing
1. Chrysanthemums
A classic autumn flower. Greenhouse-grown chrysanthemums can bloom until late November or even December. Choose varieties such as ‘Allouise Pink’ or ‘John Hughes’ for large decorative blooms. They love bright light and benefit from regular feeding.
2. Cyclamen
Cyclamen persicum brings an elegant splash of colour in shades of white, pink, red, and purple. They prefer cooler conditions, so an unheated glasshouse is perfect. Keep them moist but avoid watering the crown to prevent rot.
3. Schizanthus (Poor Man’s Orchid)
These produce orchid-like flowers in a range of jewel tones and do wonderfully in the cooler months inside a greenhouse. Ideal for adding vibrancy when other blooms fade.
4. Primula (Primroses and Polyanthus)
Early-flowering varieties of Primula can bloom in the greenhouse from autumn onwards. Their cheerful flowers brighten dull days and their compact size makes them perfect for staging or shelving.
5. Pansies and Violas
Pansies and violas can be grown outdoors too, but under glass they will produce larger, longer-lasting flowers. Consider varieties like ‘Delta Pure Rose’ or ‘Frizzle Sizzle’ for ruffled petals.
6. Salvia
Some tender Salvias continue flowering in autumn under glass, such as Salvia ‘Amistad’ and Salvia leucantha. Their spires of purple or white flowers are striking against the seasonal backdrop.
7. Begonia (Tuberous Begonias)
Tuberous begonias can flower well into autumn when protected. They need good ventilation to prevent mildew and prefer filtered light rather than direct sun.
8. Streptocarpus
Ideal for a frost-free greenhouse, these offer delicate trumpet-shaped flowers in a range of colours, often flowering well into autumn.
9. Nemesia
Autumn-flowering Nemesia brings a sweet fragrance to the greenhouse alongside their pastel shades. They thrive under glass, producing flowers until the first frosts.
10. Pelargoniums (Geraniums)
While pelargoniums are often seen as summer plants, in a greenhouse they can keep blooming until late autumn. Deadhead regularly and keep them slightly drier as temperatures drop.
Tips for Success in an Autumn Greenhouse
- Ventilation: Even in cooler months, greenhouses can heat up during sunny days. Open vents to avoid fungal issues.
- Watering: Reduce frequency but don’t let compost dry out completely.
- Feeding: Switch to a high-potash feed to encourage stronger blooms.
- Cleanliness: Clear fallen leaves and debris to reduce pests and disease.
- Lighting: Shorter days may affect flowering; consider supplemental lighting if you want to extend bloom periods further
Glass Greenhouse vs. Outdoors: Autumn Flower Performance
The graph below illustrates typical differences in flowering period and bloom quality when growing under glass compared to outdoors with no protection:
+--------------------------------------------------------+
| Flowering Period (Weeks) |
| |
| Greenhouse: ██████████████████████████ (12–14 weeks) |
| Outdoors: ████████████ (6–8 weeks) |
| |
| Bloom Size / Quality |
| |
| Greenhouse: ████████████████████ (High) |
| Outdoors: ███████ (Moderate) |
+--------------------------------------------------------+As shown, a glass greenhouse almost doubles the flowering period and significantly improves bloom size and quality thanks to protection from wind, rain, and early frosts.
Why Glass Greenhouses Work Best
While polycarbonate or plastic greenhouses also extend the growing season, glass has advantages:
- Better light transmission, especially important during the shorter days of autumn.
- Longer lifespan and less likelihood of becoming opaque.
- Aesthetically pleasing, turning your greenhouse into a focal point of the garden.
Combining Greenhouse and Garden Displays
A lovely approach is to grow the more tender autumn flowers under glass while using hardier types outdoors. For example:
- Indoors: Chrysanthemums, begonias, cyclamen.
- Outdoors: Hardy violas, asters, Japanese anemones.
This ensures your garden looks colourful right through until winter, while the greenhouse remains a haven of warmth and colour.
Final Thoughts
Autumn doesn’t have to signal the end of floral beauty in the garden. With a glass greenhouse, you can enjoy blooms deep into the season, experiment with more delicate species, and extend the pleasure that flowers bring.
Whether you choose classic chrysanthemums, fragrant nemesia, or elegant cyclamen, a greenhouse becomes your secret garden of colour, offering solace and joy on even the greyest of British days