Hydrangeas (Hydrangea macrophylla)

How well established is this crop?

This crop is a relatively new industry. It has been grown commercially for approximately 5 years. Commercial returns, current growers and some level of regional based research may be available to help those new to this industry.

Background

Hydrangeas have been growing in the gardens of southern New Zealand for many years and have recently become an export crop. When mature the bushes can be up to 2m wide and tall. They grow best in a woodland setting underneath other trees in a garden. They will not grow and flower successfully in direct sunlight, so modern commercial plantings are under large shade structures with a minimum of 50% shade.

The flowers come in a range of colours from deep blues through to reds and whites. An export market has also been established for the so called ‘antiques’. These are flowers that have been left on the bush after the traditional picking time. They mottle and take on brown and green tones. This is seen as particularly attractive by buyers and they achieve high prices in the market.

Winter Chilling and Frosts

Frosts can affect a hydrangea crop in a number of ways. Firstly, winter frosts can kill flower buds developing in stems leading to a complete loss of crop. Secondly, a late spring frost can also affect the developing flowers and stems. Late pruning is the only realistic way of combating this.

Rainfall and Irrigation

Hydrangeas are not affected directly by rainfall at any stage of growth. However, rainfall can lead to problems with fungal and bacterial diseases especially on the flowers.

If natural rainfall is not enough supplementary irrigation may be needed. However care must be taken with overhead watering systems as wet flowers and foliage can lead to an increased chance of fungal diseases. T-tape and drip systems are recommended in conjunction with a thorough fungal spray programme.

Wind

Like most high value flower crops, shelter from the wind is essential. This can take the form of natural tree shelter or artificial shelter using wind cloth. A good rule of thumb when designing shelter is to multiply the final height of the shelter by 5. Use that measurement as the distance you position your shelters apart. For example, when using 2m high windbreak cloth, you will need shelters every 10m.

If using natural tree shelter, make sure the shelters running east-west are deciduous. This will allow sunlight into the blocks in the winter. Position all shelters at right angles to the prevailing winds. Talk to your local nursery when deciding on the right tree type for your property. They may also be able to help with design.

Soil

The key physical soil requirement for hydrangeas is a relatively free draining root zone. On the other hand the soil must not dry out at all. It must have a high water-holding capacity, so soil is not too wet and not too dry.

Fertility

Hydrangeas are an unusual plant as the colour of the flower is influenced by the nutrient status of the soil. Soil with a neutral to high pH of 6.0-7.0, produce whites and reds. Soils that are more acid with a pH of 4.5-5.5 produce blue colours. This occurs because the availability of aluminium in the soils changes with the pH and it is aluminium that causes the flowers to change colour.

To grow hydrangeas successfully we need to be able to manage the soil nutrients very carefully. Aluminium sulphate is good for the blues and superphosphate and lime is needed for the reds and whites. A soil with a high cation exchange capacity will make management much easier. This can be measured in a simple soil test.

Weed Control

Weed control in hydrangea blocks tends to be relatively straightforward. The plants are aggressive growers in a darker than normal environment. Many weeds tend to be unable to grow in these conditions. Many blocks of Hydrangeas are also grown in weedmat meaning weeds cannot get established. General herbicides, hoeing or hand pulling is the easiest way to control weeds if needed.

Varieties

There is a huge number of hydrangea varieties and many more are being imported into the country all the time. Instead of varieties it is easier to talk about Hydrangea types.

Old fashioned varieties: These are the old garden type hydrangeas that we have grown up with. Those with crinkly petals tend to be the best for export.

Modern single colour varieties: These tend to be specially bred varieties grown for there flowers. They come in a range of colours.

Modern bi-coloured varieties: These have two colours on their petals.

Antiques: These are any of the above types left on the bushes after the usual picking time to mature some more.

Pests and Diseases

When grown in a home garden most hydrangaes do not need anything done to them. However when grown in a commercial situation for export agrichemical sprays are needed. The plants can suffer from several fungal diseases, most notably botrytis and powdery mildew. In some cases this can lead to complete crop loss as marked flowers cannot be sold. Only a few insects are a problem on the crop including aphids and mites and spiders. There is a zero tolerance to these insects when exporting flowers.

Layout

Hydrangeas plants grow to fill in a space approximately 1.5 x 1.5m. They can be planted in single or double rows depending on block layout. There does not seem to be a preference and in many cases several planting systems are used on the one property. The key is to make sure you have access to each plant for spraying and harvest.

General Management

Hydrangeas are a relatively high maintenance flower crop when grown commercially. After the plants come through winter they start to grow and will need pruning to set the bushes up for the coming flowering season.

Unfortunately all bushes behave differently. Some can be cut right back at ground level. They then grow a stems with a flower bud on it that same season. Other types grow flowers on buds from the previous season's growth. You need to recognise which type of bush you have, and adjust your pruning accordingly.

As the season progresses spraying and weed control will be needed. Watering and shade will also be required to ensure good flower development and stem length.

Harvest

If picking fresh the stems are taken when approximately 50% of the flowers on the head are open. Look carefully at the head for this. The true hydrangea flowers are the small buds inside each set of brightly coloured ‘petals’ They are actually not petals at all, rather modified leaves. If picking for the antique market they can be left on the bush for a further period. The first frost tends to see the end of the season. The stems should be a minimum of 40cm long but 30cm stems are sometime accepted by exporters.

Equipment

Hydrangea growing can be as high or low tech as you want it to be. The size of the block is the best determinant of this. Small blocks can be managed with a pack-pack sray unit and general gardening equipment. Larger blocks are easier managed with mechanised spray units, however all picking and pruning still needs to be done by hand.

Returns

Because most of the Hydrangea crop is exported returns vary widely depending on the season, exchange rate, world events etc. Production costs per stem to grow, pick, pack and ship, vary from 80c - $1.00. Returns vary from $1.00 right up to $2.50 (2003-04 season prices).

This past season has seen Columbia and Ecuador in some of the same New Zealand export markets, significantly affecting the price we receive. This will need to be watched carefully in the coming years.

Contacts

If you are thinking of growing Hydrangeas it is best to contact a current grower through your local Flower Growers Group.