The ideal soil mix for lavender in pots and containers is 30% course sand or gravel to 70% organic compost or potting soil. Add in a tablespoon of garden lime to the mix to raise the pH so that it is slightly alkaline. This soil mix replicates the optimal soil conditions of the lavenders natural Mediterranean range.
Keep reading for more on the specific soil requirements of potted lavenders, details on the ideal soil mix to ensure strong blooms and fragrance and how the size of the pot or container you use affects lavenders.
Soil Requirements For Lavenders in Pots
Lavenders are native to the Mediterranean region of Europe in countries such as France, Spain and Italy where they thrive in low to medium fertility, well draining, alkaline, sandy or gravelly soils.
To grow lavenders in pots successfully you need to mimic the soil conditions of their native environment in order to get the most out of your lavender, in terms of flowering, fragrance, oil and longevity.
The right kind of soil for potted lavenders is as important as how frequently you water the lavender. (For guidance on watering read my article, how often to water lavender).
Whilst lavenders do tend to thrive on neglect, they need very specific soil conditions to grow and bloom to their best. This includes:
- Alkaline soil. Your potted lavender will be most happy in alkaline soil but will grow well in soils ranging from pH 6.5-8 which ranges from mild acidity to alkaline.
- Well draining sandy or gravelly soil. Well draining soil is imperative if the lavender is to survive winter in a pot. Lavenders hate to be sat in cold wet soils as this increases the likelihood of the fungal disease root rot. The soil must drain very quickly and not retain much water as the lavenders roots like to dry out between each watering.
- Low to medium fertility. Lavenders have specifically adapted to sandy soils that are relatively low in nutrients. A common mistake by gardeners is to plant lavender in rich soils and add fertilizer to encourage the plant to grow and flower. Lavenders in high fertility soils will grow leggy with lots of foliage grow and fewer flowers. An excess of nitrogen will turn the lavender foliage yellow.
- Open soil structure. Lavenders prefer a porous soil structure with a relatively high course sand or gravel content as this allows water to drain effectively and supplies oxygen and creates space for the roots so that they can establish. Lavender do not do well in compacted soil.
The Optimal Soil Mix for Lavenders in Pots and Containers
Now we know the soil lavenders prefer in their native range, we need to go about replicating these conditions for potted lavender.
The most important factor is to ensure the soil mix contains a good amount of coarse sand or gravel. Both of these materials work very well for lavender growing and providing the optimal structure for good drainage.
However it is important to emphasize that coarse builders sand is far superior to fine sand which is much smaller in terms particles size and therefore less porous.
Lavenders need oxygen in the soil for root respiration and to lower the chance of root rot. This is why it is imperative to mix the large particles of sand and gravel evenly throughout the soil mixture when planting lavender in pots.
Only the large course sand particles or gravel will provide the right structure so that there is enough oxygen in the soil and the right conditions for water to infiltrate effectively.
One of the most common reasons lavenders die is because the soil retains too much moisture. Additional watering will compound the problem and the plant inevitably suffers from root rot.
This is why the sand or gravel is so important for maintaining the optimal soil structure. Sand and gravel also do not absorb and hold water in the same way rich organic soils do, hence the importance of mixing compost and minerals to find the right balance of soil moisture for lavenders.
When preparing lavender in pots I always recommend an inch layer of gravel in the bottom of the pot to help ensure that the drainage holes in the base of the pot remain clear and well draining.
Sand or gravel should make up around 30% of the volume of the soil mix with 70% well rotted compost or store bought organic potting soil.
You can approximate this by eye, but too much sand or gravel is always better for the lavender then not enough so be on the generous with your amendment.
The organic soil when mixed with the sand or gravel will provide the right balance of nutrients, drainage, and texture for lavenders to grow well and produce the most flowers and fragrance.
Make sure that each component is mixed throughout the soil so that soil structure remains even and the deeper roots also have good access to oxygen.
Sand and gravel do not contribute significant nutrients to the soil which will balance out the fertility of the compost so you can recreate the low to medium fertility conditions of the lavenders native Mediterranean environment.
Avoid potting soil that has been enriched with nutrients as the higher fertility soil will promote leggy growth with fewer flowers.
Store bought potting mixes tend to be pH 7 (neutral) but I would recommend that you add either some agricultural lime (about a table spoon) or wood ash to the soil to ensure your potted soil for your lavender is in the optimal alkaline range.
Avoid using any compost that contains manure as this will be too high in nitrogen and soluble salts for growing lavenders.
Ensure that when you are planting the potted lavender in the soil mix that you do not firm the soil around the lavender as this will push the air out and make it more difficult for the roots to establish.
The Size of the Pot is Important
To grow lavender successfully, the pot should ideally be 16 inches across and proportionally deep. This will guarantee that the pot holds enough soil so that the roots have enough access to moisture and nutrients as well as space to establish.
A pot or container of this size also contains enough soil to insulate the roots from cooler weather and prevent the soil from drying out so quickly in the hot weather of summer.
Choosing the right pot is important for healthy lavender which is why I have a article on which pots and container are best for lavender growing.
If you are moving the lavender from one container to another then read my guide on how to transplant lavender successfully to learn how to mitigate transplant shock.
- The ideal soil mix for lavender in containers in pots has 30% sand or gravel with 70% organic potting soil. Add a tablespoon of lime to ensure the soil is alkaline which is the preferred soil pH of lavenders.
- The sand or gravel will ensure that the soil has the optimal structure for growing lavenders so water can infiltrate and the roots have access to oxygen. The sand or gravel also helps to recreate the low to medium soil fertility that lavenders need to flower their best.
- Make sure that the organic compost and sand is mixed evenly throughout the pot.
- Add a layer of gravel at the base of the pot to keep the drainage holes clear so excess water can escape.
- A 16 inch diameter pot will ensure that the pot or container has enough soil to keep the roots insulated in winter, and the roots have enough space to establish and access the nutrients and water for a healthy lavender plant.