Plant Doctor Archive

Lavender woes

We live in Hamilton in a suburb built on clay soil. We have planted a drift of about 30 lavenders under 3 olive trees with a lonicera hedge surrounding it. The lavenders grew well for a year and flowered beautifully at the beginning of spring. Now the lavenders are dying off and we have lost about 12 of them. They seem to die from the base up. We have a watering system so they are not too dry, but we have not excessively watered either. It has been suggested that it could be a dog peeing on them, but it would have to be a fairly prolific dog to have done so many over such a large area. Do you have any ideas?

Clay soils are not the best for growing lavender and they are dying off because we have had a very wet summer without enough heat. Improve drainage by raising beds or digging in generous quantities of peat or compost.

Lavender is easy to grow when given the conditions it enjoys — a sunny position and free draining soil.

Most lavenders suitable for home gardens come from either the Spica group or the Stoechas group.

The Spica group includes English lavenders (Lavendula angustifolia syn. L. spica) which have the best fragrance and are at their peak flowering period in the heat of summer. The flowers retain their perfume and so are ideal for pot pourri or scented sachets. They also make stunning low hedges. English lavender is relatively frost hardy once established.

Stoechas type lavenders are characterised by their 'rabbit ear' sterile bracts that sit above the flowers. These include the most commonly grown French lavender (Lavendula dentata), Spanish or Italian lavender (Lavendula stoechas) as well as many cultivars bred from these varieties. They do not have the same intense fragrance as English lavender, but are certainly fragrant.

Stoechas types flower from early spring through to late autumn and sporadically through winter in warmer climates. Stoechas types have a compact growing habit making them ideal for containers and patio pots and tubs.

Most lavenders do not enjoy humid conditions and do not grow well in areas with high rainfall. Stoechas types will stand up to humid conditions better than English lavenders. Protect stoechas lavenders from frost. Once established they will withstand mild frost, but in areas experiencing severe frost, plant them in a sheltered position or in pots.

Lavenders planted in the garden generally do not require fertiliser. An application of Osmocote or general garden fertiliser in spring will help plants establish quickly and enhance flowering.

Pruning is essential to keep plants bushy and prevent them from becoming woody and bare. It also helps encourage more flowers. English lavenders are best trimmed after flowering has finished in summer so that new growth has time to harden off before winter. Trim to shape, removing old flower heads. Some varieties do not regrow in a uniform shape and so more severe trimming is required.

Stoechas types flower in early spring and in warmer climates there could be two flushes. Trim back the first flush in summer. In frost prone areas leave trimming the second flush until late winter/early spring so that new growth is not frosted in winter. In warmer regions trim back in autumn.

If growing lavenders in patio pots and tubs, use a quality potting mix that contains a controlled release fertiliser. Keep plants well watered, in summer it could be as frequent as once a day. In winter keep watering to a minimum. Feed container grown plants with a controlled release fertiliser such as Osmocote. Plants will benefit from the occasional liquid feed with a soluble fertiliser such as Phostrogen or Thrive Flower and Fruit.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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