How to Grow Onosma Plants

Guide to Growing Golden Drop

Onosma are hardy perennials that range from 15 to 45 cm (6 to 18 inches) in height.

Onosma plants bloom in the summer. They carry tubular flowers of pink, yellow, or white that are surrounded by green calyxes.

Some common names of this popular rock garden plant include Golden Drop and Golden-flowered Onosma.

Onosma alborosea
Onosma alborosea photograph by wlcutler.

Onosma javorkae picture by elisabetta2005.

Onosma Growing and Care Guide

  • Common Names: Golden Drop.
  • Life Cycle: Hardy perennial.
  • Height: 6 to 18 inches (15—45 cm).
  • Native: Mediterranean and western Asia.
  • Growing Region: Zones 5 to 9.

  • Flowers: Summer.
  • Flower Details: Lobed calyx surround clustered purple, pink, white or yellow tubular flowers.
  • Fruit: Small ovoid nutlets.
  • Foliage: Hispid leaves.

  • Sow Outside: Cover seeds. Autumn.
  • Sow Inside: Germination time: one to two months. Temperature: 50°F (10°C). Ten weeks to three months before expected last frost. Transplant outdoors following the last frost. Spacing: 6 to 18 inches (15—45 cm).

  • Requirements and care: Full sunlight. Good drainage. Dry, gritty, poor soil. Regular watering. Regular watering during dry periods. Water during prolonged dry spells. Regular watering during periods of growth. In the spring supply a top dressing of cow manure. Mulch with rock chips to maintain coolness. Provide a winter compost mulch. Propagate: by taking cuttings in the summer.
  • Family: Boraginaceae.
  • Miscellaneous: The Onosma genus contains between 85 to 150 species and belongs to the Boraginaceae family. It is therefore closely related to the borage and forget-me-nots.

How to Grow Onosma

When growing Golden drop outdoors from seeds they should be sown in the autumn. Once sown lightly cover the golden drop seeds.

Onosma genus plants like to grow in sunny conditions and have a preference for a gritty, dry and poor soil.

Indoors it is best to start growing Golden drop and other Onosma about three months before they are due to be planted out after the last frost of spring.

It takes from one to two months for Golden drops to germinate at 10 degrees Centigrade (50°F).

Once ready transplant, Onosma species into the garden with a spacing of 15 cm (6 inches; small) to 45 cm (18 inches; large varieties).

Caring for Golden Drop in the Garden

In the spring it is best to add manure to the soil around Golden drop. Mulching with rock chippings can help to keep the roots cool.

Unfortunately, Onosma are susceptible to rotting in the winter, so it is best to mulch a second time, but with organic matter.

Although perennials, Onosma are short lived. More plants should be propagated to replace them every few years. This can be achieved by taking cuttings of golden drop in the summertime.

I hope that you enjoyed this guide on how to grow Onosma plants. You may also enjoy the following Gardener's HQ growing guides: How to grow Heliotrope, Amelanchier alnifolia, and Lithodora plants.