Lavender Grosso (Lavandula x intermedia) is one of the most versatile lavender hybrids that has combined the cold hardy qualities of English lavender and the longer flowering season and fragrance of French lavender.
Lavender grosso key guide:
- Requires full sun
- Preferably Alkaline soils (can grow in soil pH 6.5 to 8)
- Water only once every two weeks in the growing season
- Requires low to medium medium fertility soil
- Soil mix needs to be amended with sand or gravel for good drainage
- Flowers for around four weeks from middle of July until late August.
- Cold hardy to USDA zone 5 and can tolerate frost and snow.
- Requires pruning once per year in either early spring or late fall
- Grows to 46 inches wide and 36 inches in height at full maturity.
- Grows very well in pots, containers, raised beds and well draining garden soil.
- Grosso is valued for its fragrance and oils and is grown commercially.
Keep reading for all the information you need to grow and care for lavender Grosso and ensure the plant produces the most amount of flowers and sweet aromas for as long as possible…
Where can you Grow Lavender Grosso?
Lavender Grosso is a perennial sub shrub that is a hybrid of French and English lavenders.
Lavender Grosso is a variety that has been cultivated to retain the cold hardy characteristics and longevity of English lavender (so it can be left outside over winter, whereas French lavender requires winter protection) and the longer flowering season and fine fragrance of the French lavender species, so you get the best of both worlds.
This variety can grow in cool temperate climates, tolerate frosts, snow and ice in winter and regarded has cold hardy to USDA zone 5.
Grosso requires full sun, with well drained soil and appreciates an occasional breeze to prevent fungal diseases. It will not grow very well in humid climates (as with all lavender varieties).
When Does it Flower?
The exact time of flowering will depend on the climate but lavender Grosso usually flowers in mid to later summer from July through to August and will bloom for several weeks. Regular deadheading will promote more flowers.
Pruning in the late summer after flowering will promote stronger blooms the next year, maintain a nice tidy shape and extend the life of the lavender.
What is The Best Time for Planting?
Spring is the best time for planting as the lavender has the entire growing season of warm weather for it roots to grow and establish in the soil, although this hardy variety can be planted in summer and early fall without a problem.
Lavenders usually put on their best display of blooms the season after they are planted, however I wrote an article on the steps that you can take to help mitigate transplant shock, so that your plant flowers as much as possible in its first year.
Winter planting is to be avoided as the roots will be planted into cold soil during the lavenders dormancy and they will struggle to establish.
Care Guide: Lavender Grosso
Watering lavender Grosso is very low maintenance once you know how to water the plant at each stage of growth.
Lavender is a drought resistant plant has adapted to growing in climates with little rainfall and relatively dry soils and therefore it does not require frequent watering.
Problems with lavender care are usually because the gardener is watering the plant too often which leads to root rot. The signs of stress from over watering are brown foliage and a drooping appearance. (If this has happened to your lavender, read my article for the solution).
If you plant lavender Grosso in well draining soil and water the established plant once every two weeks in the growing season then you will avoid problems associated with over watering and the plant will produce flowers and aromas every year.
Always water with a generous soak to encourage roots to grow deep into the soil so the lavender can access the nutrients and water it needs. A light watering will result in more shallow root growth which makes the plant less resistant to drought.
- Newly planted lavender. If you have just planted your lavender in the ideal spot or recently transferred it from one place to another, then the lavender will require more water as it settles into its new home. Water Grosso lavender straight after planting with a generous soak and then water once every other day for the first week. After the first week scale back the frequency of watering to once every 3-4 days for the first three months. After three months water once every two weeks during the growing season.
- Established lavender. Lavender that is established (longer then three months) will only need water once every two weeks during the spring and summer months thanks to its natural drought resistance. Do not be tempted to water more then this, as a lot more problems result from over watering lavender Grosso then under watering. Over watered lavender will look brown and droopy and will be much more susceptible to root rot. If they has been significant rainfall and you can detect moisture to a fingers depth in the surrounding soil then skip watering for a few days till the soil has dried out before watering again.
- Grosso lavender in pots and containers. Give lavenders in pots a good soak so that water trickles out the base of the pot. Water once every two weeks in the growing season just like an established lavender. Pots can dry out quicker when it is the growing season and the lavender is in blazing sun with high temperatures, but do remember, lavenders are drought resistant plants that like the soil to be somewhat dry between bouts of watering. It is essential that the pot measures at least 16 inches across so that it holds enough soil, so the pot does not dry out too quickly in summer and provides some insulation for the roots during winter. In hot weather water Grosso potted lavender every 10-14 days with a generous soak.
- Watering in Winter. Lavender enters a state of dormancy over winter and therefore requires less, if any water. Lavender Grosso is cold hardy to USDA zone 5 and can tolerate frost and cool temperatures and therefore can be left outdoors in most cool temperate climate. Lavender will attain enough water from the environment over winter if left outdoors and does not require additional water. Lavenders do not like to be in cold wet soils over winter, so ensure the soil is well draining and do not water the plant until the temperatures warm up again in the spring.
Plant lavender Grosso in full sun for best results. The less sun a lavender receives the less flowers it will produce so ensure that you plant it in the sunniest spot in your garden. (For more tips read my article, reasons why your lavender isn’t flowering).
If you are struggling for space in your garden then I recommend planting Grosso in a pot and finding a location with full sun, rather then trying to compromise by planting in partial shade.
Full sun will also reduce the chance of fungal disease and will dry any residual moisture from rainfall that can cause problems and maintain a healthier plant.
Optimal Soil for Lavender Grosso
Lavender Grosso is a hybrid of both English and French lavender species, which has been cultivated for the hardy growing characteristics of English lavender (read my article on hardy English lavenders for more info).
This plant has retained English lavenders greater tolerance of slightly acidic soils and will flower in soils with a pH of 6.5 to 7.5 (slightly acidic to alkaline) therefore it is likely more suitable for growing in your garden soil.
If you have acidic soil and want to grow lavender then read my article for some easy solutions.
Here is a run down of lavender grosso soil requirements:
|Soil Characteristics||Lavender Grosso Soil Requirements|
|Well draining soil||The most important criteria is that the soil must be well draining. Lavenders are native Southern Europe where they grow in sandy or stony soils that allow water to infiltrate quickly and do not retain moisture. Lavender Grosso as with all lavender varieties is susceptible to root rot when planted in watering retaining soil such as clay or rich organic soils.|
|Low to medium fertility||Lavenders are adapted to living in sandy soils that are relatively low in fertility. Lavender Grosso will not blooms or produce fragrance to its full potential if the soil is rich in nutrients. High fertility soils lead to soft, leggy growth with fewer flowers.|
|Soil pH||As lavender Grosso is French and English species hybrid, it is able to grow in soils with a pH of 6.5 (slightly acidic) to pH 8 (alkaline).|
|Soil structure||The preferred soil structure is a soil that is light and non compacted. The soil needs to be porous so that water can drain efficiently and oxygen can reach the roots for respiration. This structure can be achieved by amending the soil with course builders sand or gravel.|
Good drainage, low to medium fertility and porous soil structure are all soil characteristics of the lavenders native mediterreanean home and can be replicated in your garden by amending the soil with builders sand or gravel.
Sand or gravel creates the perfect soil structure for optimal porous soil that allows water to drain away from the lavenders roots which helps prevent root rot.
Sand or gravel will balance the fertility of organic soil as sand does not contribute nutrients to the soil and therefore recreates the low to medium fertility conditions that lavender Grosso loves to grow well and produce the best yield of flowers and oil and to produce the finest fragrance.
Soil that is composed of 30% sand or gravel and 70% organic potting mix or garden soil is optimal. Add some lime to the soil to increase the alkalinity if you have acidic soil. For more guidance read my guide for the optimal soil mix for lavenders.
How Far Apart to Plant Grosso Lavender
Lavender Grosso is a large cultivar of lavender that will spread out its foliage at full maturity up to 46 inches (116 cm) wide and 32 inches (80 cm) tall.
Therefore it is important that you plant lavender Grosso at least 2-3 feet from each other. This will ensure that each plant has enough air flow, water, nutrients, sunlight and space for roots to establish in the soil.
Lavender Grosso appreciate airflow (as all lavender do) around the foliage as this will help to reduce the chance of fungal disease and keeps the foliage and stems nice and dry, which is why the plant loves to grow in an open sunny space.
Bear in mind that 2-3 feet of space includes other plants, fences, walls and anything else that may limit airflow and cast shade on the lavender.
It should be noted that Grosso will grow larger in warmer climates and stays more compact in colder climates, so expect some regional of size variation depending on your location. Either way it will still display plentiful blooms and produce its fine fragrance regardless of size.
Pruning lavenders of all kinds is essential for maintaining the plants overall shape and appearance, promotes flowering, prevents leggy growth, slows down growth of the woody base and extends the life of you lavender.
If you do you research on pruning lavender you will find some gardening experts like the Royal Horticultural Society will recommend pruning lavender in the late summer after the plant has bloomed.
However many commercial growers insist lavenders should be pruned in the early spring in order to stimulate growth and blooms such as this grower in Oregon.
My advice for pruning lavender Grosso is that if you are in a cold climate, you should prune the soft green stems back by about a third in the spring into a nice round mound shape.
Then you can do a gentle prune to maintain shape and perhaps harvest the flowers or deadhead any faded flowers in the middle of august.
If you are in a colder climate and you give lavender Grosso a hard prune late in late summer then there is less time for the plant to repair its wounds in time for winter frost and therefore it will be more susceptible to damage. (Read my guide on winter care for lavenders).
However if you are in a warmer climate that does not typically experience frosts in winter then you can prune lavender Grosso in the late summer or early fall. Grosso is cold hardy and it will not be troubled by winters in mild climates.
Never cut back into the woody growth of the lavender as it will not rejuvenate. Always leave at least two inches of softer greener growth above the brown woody base of the lavender. Pruning lavender is like pollarding a tree in that the lavender will live longer and the plant will be healthier for it.
In Pots and Containers
This variety grows very well in pots and containers because of their favourable drainage conditions.
However it is important to choose the right pot to grow Grosso. The pot should have drainage holes in the base and measure 16 inches across. Avoid placing the pot on a drip tray or in a larger decorative pot that does not allow for drainage as the soil will quickly become saturated which will lead to root rot.
I have a guide on choosing the best pot for growing lavenders which tells you all you need to know.
Caring for potted lavender Grosso is very similar to caring for lavender planted in gardens, they require the same soil mix, sunlight, pruning and watering. For more information, take a look at my article on caring for lavenders in pots.
It is possible to grow this lavender indoors although because it has a large spread at maturity I would recommend a smaller variety such as Lavandula angustifolia ‘Hidcote superior‘ which is far more modestly sized 16 inches by 18 inches (40 cm by 45 cm) and therefore is far more lightly to fit on a window sill (all lavenders need as much sun as possible).
- Lavender Grosso is a hybrid of French and English lavender. Grosso retains the cold hardy characteristics of English lavenders and the longer flowering season of French lavenders.
- The best time to plant is in the spring when the weather has warmed up, although this hardy variety can be planted can be planted up until early fall. Always plant in full sun for best results.
- Lavender Grosso is cold hardy to USDA zone 5 and can tolerate winter frosts, snow and ice.
- Grosso is a larger variety of lavender that grows 46 inches wide and 36 inches tall. For best results plant this lavender 2-3 feet away from other lavenders or plants, for good airflow and to ensure other plants are not casting shade which will reduce blooms.
- Grosso is drought resistant and only needs watering once every two weeks when it is established.
- Pruning every year is important to maintain appearance, promote blooms, and extend the life of the lavender.
- The soil needs to be well draining, between pH 6.5-8, low to medium fertility, with a porous structure, which can be achieved by amending soil with sand or gravel and lime if your garden soil is particularly acidic.