Growing Rosemary in the Greenhouse

Rosemary (Rosmarinus officinalis) is a versatile and aromatic herb that has been cherished for centuries for its culinary, medicinal, and ornamental properties. Growing rosemary in a greenhouse provides an ideal environment for this herb to thrive, especially in the ever changing climate of the United Kingdom. In this comprehensive guide, we will take a look at the various aspects of cultivating rosemary in a greenhouse, covering everything from selecting the right variety to providing optimal growing conditions.

Choosing the Right Variety

Rosemary comes in various cultivars, each with its unique characteristics. When selecting a variety for greenhouse cultivation in the UK, consider factors such as growth habit, flavour profile, and adaptability to indoor conditions. Some popular varieties for greenhouse cultivation include ‘Tuscan Blue,’ ‘Arp,’ and ‘Barbecue.’ It is available as upright, trailing and tree type plants.

Preparing the Greenhouse

Before planting rosemary, ensure that your greenhouse is well-prepared to create a conducive environment for its growth. This involves maintaining adequate ventilation, providing proper lighting, and controlling temperature and humidity levels. Rosemary thrives in well drained soil, so make sure to use a well-balanced potting mix with good drainage properties.

Planting Rosemary

When planting rosemary in the greenhouse, it’s crucial to consider spacing and container size. Use containers with good drainage holes to prevent waterlogging, and leave sufficient space between plants to allow for air circulation. Plant rosemary in late spring or early summer to take advantage of the growing season.

Water and Humidity

Rosemary prefers slightly dry conditions, so it is essential not to overwater. Allow the soil to dry out between watering sessions. Greenhouse environments can sometimes become humid, so ensure proper ventilation to prevent fungal issues – Access Mini greenhouses are ideal for this as their sliding door design allows lots of ventilation. Consider using a drip irrigation system to deliver water directly to the soil without wetting the foliage excessively.

Light and Sunshine

Adequate light is essential for the healthy growth of rosemary. Place the plants in a location where they ideally receive at least 6-8 hours of direct sunlight per day. If natural light is insufficient, supplement it with artificial lighting, especially during the darker winter months.

Temperature

Rosemary is native to the Mediterranean region and thrives in warm conditions. Greenhouse growers in the UK should ideally maintain a temperature range of 60-70°F (15-21°C) during the day and slightly cooler at night. Consider using a greenhouse heater during extremely cold months to ensure a stable temperature.

Feeding and Fertilising Rosemary

Rosemary is a relatively low-maintenance herb, but it will benefit from occasional feeding during the growing season. Use a balanced, water-soluble fertiliser and apply it according to the manufacturer’s instructions. Avoid over fertilising, as this can lead to excessive foliage growth at the expense of flavour.

Pruning and Harvesting

Regular pruning helps maintain the shape of the rosemary plant and encourages bushier growth. Prune the tips of the branches regularly, but avoid cutting into old wood, as rosemary may struggle to regenerate from woody stems. Harvest leaves as needed, but ensure not to remove more than one-third of the plant at a time. If you harvest lots of rosemary, it can be frozen which will preserve the oil that gives this herb its distinctive smell and flavour.

Potential Problems

While rosemary is generally resistant to pests and diseases, it’s essential to monitor for any signs of trouble. Aphids and spider mites can occasionally be a concern. Use insecticidal soap or neem oil for organic control. Ensure good air circulation to prevent fungal issues, and promptly remove any affected leaves. Avoid overwatering as this can cause root rot.

Overwintering Rosemary in the Greenhouse

Winters can be challenging, so overwintering rosemary in a greenhouse is a practical approach. Reduce watering by at least half during the winter months and protect the plants from extreme cold. Consider using horticultural fleece or bringing potted rosemary indoors during severe cold spells.

Conclusion

Cultivating rosemary in a greenhouse offers an excellent solution for ensuring a consistent supply of this aromatic herb all year round. By providing the right growing conditions, including proper light, temperature, and well drained soil, greenhouse growers can enjoy the benefits of fresh rosemary for culinary, medicinal, and decorative purposes. With attention to detail and regular care, growing rosemary in a greenhouse can be a rewarding and successful endeavor for gardening enthusiasts. Rosemary not only tastes good, it is a good source of calcium, iron and vitamin B6. It is also considered to support memory retention and other health benefits such as anti-inflammatory, antioxidant and calming properties.