Last updated 26/06/2019
This article is the first in a series of growing Lavender in tropical Singapore. The second part on root pruning is available here.
Lavender is a familiar herb that almost every gardener wants to grow and needs little introduction. The genus Lavandula is native to Africa, parts of Europe, the Mediterranean and southwest Asia, and they are usually grown in temperate and subtropical climates across the world.
Most commonly used for culinary and medicinal purposes are English Lavender (Lavandula angustifolia), French Lavender (L. dentata), and Spanish Lavender (L. stoechas), while Lavandin (L. x intermedia) is mostly used for perfumery and essential oil production.
As these plants come from a Mediterranean climate of hot dry summers and mild wet winters, they present a unique challenge to many gardeners in lowland tropical regions.
The bulk of lavender plants for sale locally are imported from Cameron Highlands in Malaysia, and these are usually Lavendula x ginginsii 'Goodwin Creek Gray', one of the more vigorous and heat tolerant hybrids. Other cultivars like the Bandiera series, as well as other species such as L. stoechas, mainly come from Japanese and European growers.
For us here in the humid tropics, imported plants often decline rapidly due to a combination of two main factors, improper care and the failure of the plants to acclimatise to a much warmer climate. Onset of root rot and fungal diseases, suspected to be caused by plant pathogens such as Erwinia or Phytophthora often begin rapidly with symptoms usually appearing from the base of the plant, with leaves dying and progressing towards the top. Plants often die within days or weeks.
▲ Plants in various stages of decline. Photo credits: Gina Koh (left) and Thersa Wong (inset)
Since 2017, I've been conducting ongoing trials of various lavender species and cultivars, and here are the best practices based on our own research.
Many of the plants are already in various stages of decline if they have spent any time in the local garden centers, exposed to frequent rain and overwatering, so it is crucial to purchase fresh arrivals.
It's highly recommended to take cuttings from them to increase chances of survival, and to grow those cuttings hydroponically, as that takes the guesswork out of watering and allows easy observation and early detection of any root issues where most of the problems start. Treatment such as trimming is also much easier if there is no media in the way. Furthermore, growing them indoors with growlights means a generally cooler environment and protection from the rain, reducing risk of fungal infection.
Here's our step-by-step guide what to do.
1. Rooting cuttings
The easiest method for propagation is to take tip cuttings from any newly bought plants and root them in a small amount of water (about a depth of 1 cm maximum). Expose cuttings to bright light, and they will sprout roots in about 7-10 days.
▲ Note the amount of water used for rooting.
2. Transferring to the nutrient solution
Once the roots have grown longer than 2-3 cm, place them in a mesh pot with leca or any other inert media, and place the mesh pot into a larger container where it will fit over the opening. The nutrient solution is filled to 1 cm above the base of the mesh pot. As the plant grows, the nutrient solution can be lowered until the level shown in the first photo above.
This method of growing has been trialed on other herbs such as Rosemary, Sage, Thyme and Mint and results have been very successful.
3. Plant care
These herbs, with the exception of mint, grow best with a low nutrient solution, with an EC of 1.0-1.5. We use the HYDRO POWER C solution at 1 ml of fertilizer to 1000 ml of water. The nutrient solution is changed every 1-2 weeks, and meanwhile the bottle is kept replenished with just water up to the level shown in the first photo above.
For these herbs, grow lights with a PPFD of about 250-350 µmol/m2/s2 for 12-14 hours per day is sufficient, or they can be grown on a sunny windowsill that has at least 6 hours of direct sunlight per day. Remember to cover the transparent containers to prevent algae from proliferating in the nutrient solution. Plants grow very fast under these optimal conditions, and from cuttings to a shrub takes around 6-9 months or so.
As a result of our trials, we have now have several plants with more varieties coming soon that are available for purchase from the store (only available in Singapore). We're also available for workshops and consultation for projects, please get in touch with us for more info.