Lavender will not grow well if it is planted directly into clay soil. Clay soil retains too much water which will lead to the disease of root rot, however you can grow lavender in clay soils if you significantly amend the soil beforehand with gravel to drastically improve the drainage and soil structure.
Clay soils can also be problematic for lavender growing from the perspective of:
- Clay soils are high in nutrients. Lavenders are specifically adapted to growing in poor quality, low nutrient, sandy soils in the Mediterranean region of Europe. High fertility soils promote foliage growth at the expense of flowers, which gives the lavender a leggy, and untidy appearance.
- Clay soils are very susceptible to compaction and can bake hard in persistent sunshine which makes it impossible for lavender roots to establish.
- Clay soils tend to be acidic whereas lavenders do tolerate mild acidity (pH 6.5) but prefer alkaline soils up to pH 7.5.
There are still some good options for growing lavender if you have clay soils. Here’s what you can do:
- Amend the clay soil, with aggregate (grit or gravel) to improve the texture a maintain the right level of fertility.
- Create raised beds and use amended soil.
- Plant lavenders in pots.
How to Amend Clay Soils for Lavender Growing
Building Sand is frequently recommended for amending soil for lavender growing as it replicates the sandy soil conditions of the lavender’s native Mediterranean home range.
However clay soils are prone to compaction and therefore, sand is less able to retain a porous, well draining soil structure in clay soils as it is too fine. I have personally seen a garden where heavy clay had been amended with sand and over time the soil was thick and formed almost an impermeable cement like texture.
Gravel however is much better at maintaining a structural integrity in clay soils over long periods of time. The large particles interlock in a way that leaves more air pockets in the soil to allow water to effectively infiltrate and roots to establish in the soil, which is ideal for amending clay.
If you garden is made of particularly heavy clay and is therefore notably slow draining then the greater the area you amend around the lavender the better.
Otherwise water can collect at the point the amended soil meets with the clay. Always choose a higher area of your garden to plant your lavender (as it will have naturally better drainage) then a lower lying area which will typically drain slower.
Top tip: Avoid trying to dig or work heavy clay soil when it is wet as it will be very slick and stick to your boots and shovel, rather then digging cleanly. This can be very frustrating!
1. To amend the soil you will need to dig out an area of clay 18 inches wide and 12 inches deep as this will accommodate all lavender species when they reach full maturity.
2. Dispose of the heavy clay soil or redistribute elsewhere in the garden.
3. Replace the clay with a mixture of garden compost (or a soil mix) and gravel with a ratio of around 30% gravel to 70% compost.
4. Make sure that the compost and gravel is mixed evenly throughout the amended area of soil. You can do this with spade but personally I like to use a trowel to ensure each component is distributed equally.
5. Plant the lavender in the hole and back fill with sand and compost. Firm the lavender in the hole with your hands to give the plant some stability but do not tread in with your heel as this will compact the soil and make it difficult for the roots to establish.
6. Give the lavender a good soak with which should help to alleviate transplant shock.
For more information about planting, watering and caring for newly planted lavender, take a look at my article: How to Transplant Lavender.
Should I add Mulch to Lavender in Clay soils?
The best type of mulch for lavender in clay soils are materials such as wood bark, white gravel or limestone. Organic matter like, compost or leaf mould will hold into too much water and potentially lead to root rot whereas gravel or wood bark let water drain through the soil and suppress weed growth.
An added benefit of white gravel or limestone is that the white colour reflects light effectively back onto the foliage for more sunlight and heat around the plant, effectively creating a micro climate. This is a tip I learned from commercial lavender growers in California to increase lavender fragrance and oil production.
Limestone will contribute to the soils alkalinity over time which is a good way of maintaining the right soil pH for lavender (pH 6.5- pH 7.5) if you have naturally acidic soils.
Alternatively if the conditions are not favourable, you can choose raised beds, or pots to grow lavender. Lavender also needs, full sun, low to medium fertility, good drainage and infrequent watering which can be difficult conditions to cater for with clay soil but it is very easy to achieve with pots or raised beds.
Alternatives for Lavender Growing in Clay Gardens
A good way to avoid the problems posed by clay soil is to either create a raised bed for lavender or plant lavenders in pots.
Both of these options are very favourable for growing lavender because:
- Pots and raised beds are a great way to raise lavenders out of damp soils and improve drainage.
- You can accurately add the right proportions of sand/ gravel (approx 30%) and compost (approx 70%) to replicate the lavenders preferred conditions of their Mediterranean environment (in terms of soil fertility and drainage) without having to dig out and remove large amounts of clay.
- Pots can be moved inside before winter to prevent frost damage. (French, Spanish, Italian and any other non English lavender species are not frost tolerant. Only the English varieties are cold and frost hardy).
Take a look at my article How to Grow Lavenders in Pots for everything you need to know about caring for potted lavenders.
Growing lavender in pots requires less skill and significantly less labour then creating a raised bed, however raised beds can still be an inexpensive and effective solution to growing plants in heavy clay soils.
Take a look at this video for the easiest and least expensive raised bed creating tutorial:
- Clay soils retains too much water for lavender growing. Lavenders prefer well draining soil that does not hold onto moisture.
- To grow lavenders in gardens with clay soil, you will have to dig a hole 18 inches wide and 12 inches deep and replace the soil with a 70% compost and 30% gravel mixture before planting the lavender to provide the favourable drainage and low to medium fertility conditions that lavenders require.
- Always use gravel or grit instead of sand for better soil structure when amending clay soils.
- Avoiding digging clay in wet conditions as the clay will be slick and stick to your spade. Always wait for a dryer day instead.
- Planting lavender in pots is a less labour intensive alternative that provides more favourable conditions for lavender growing then preparing and amending clay soils.