Growing Zucchini Marrows (Cucurbita pepo L.)

Note Number: AG0259
Published: April 1995
Updated: June 2011

Zucchini is an immature vegetable marrow. It is a member of Cucurbitacea family (also known as the Gourd family) which also consists of pumpkins, cucumbers, squash, and melons. Zucchini is one of the easiest vegetables to cultivate in temperate climates.

Zucchini is 96% water and is low in energy and carbohydrates. It contains useful amounts of Vitamin A (as carotenoids called lutein) and B (as folate), potassium and manganese.

Zucchini and marrows (larger more mature zucchini) are annuals, have a bush habit and are frost-prone at all stages of growth. Rapid germination and vigorous growth occur when soil temperature reaches 20°C. First fruits can often be harvested from 40 to 50 days after sowing.

Varieties

Zucchini are usually dark green, but may also be yellow or light green and they have a similar shape to a cucumber. There are a few cultivars with round or bottle shaped fruits.

Most commercially grown zucchini cultivars are hybrids because they are usually heavier producers than open-pollinating types.

Zucchini bears separate male and female flowers and pollination is assisted mainly by bees. If poorly pollinated, fruits will fall off and if partially pollinated fruit will develop unevenly.

Disease resistant or tolerant cultivars may be the most appropriate types for areas prone to certain problems like Watermelon Mosaic Virus (WMV) or mildews. There is a range of resistant and tolerant varieties available. Tolerant varieties show few symptoms of infection where as resistant varieties have a reduced level of infection.

Many cultivars are available. Some of the more commonly grown varieties are Congo, Calendia, and Hummer other dark green varieties include Blackjack, Stinger and Midnight. Lighter-skinned cultivars known as Lebanese zucchini include Columbia, Greyzini and Nebo. Yellow or golden cultivars include Sunburst, Gold Coast and Goldsmith. These are just a few of the cultivars available and growers should consult seed companies for latest cultivars as new ones are released frequently.

Soils

Light soils that warm quickly are suitable for early sowings; heavier soils are better suited to plantings that will be producing through the heat of late summer and early autumn. Early season plants may be grown in plastic covered beds to hasten soil warming and reduce weed competition.

Whatever the soil type, the crop will do best if the soil is well structured and drained and has plenty of organic matter. Crops are normally grown on raised beds and the top 5 cm of the bed should be loose to allow the seedlings to emerge freely.

Fertilisers

If necessary, apply lime to raise the pH to about 6.0 to 6.5. In this pH range, most nutrients present in the soil are available to the plants without being at toxic levels. One or two weeks before sowing, apply a complete fertiliser mixture at the rate of 750 to 1100 kg per hectare (from 75 to 110 g per m2) depending on soil type and fertility. Fertile soils will require lower rates of basal fertiliser and NPK of 5:8:4 or 6:6:6 are suitable. For low fertile soils NPK of 8:11:10 is suitable with reduced rate of about 550 to 880 kg per hectare.

Side-dressings at flowering or fruit-set need only contain nitrogen and/or potassium. NPK of 20:0:16 at 225 kg per hectare is adequate or if the soil is rich in potassium, apply 45 kg per hectare of sulphate of ammonia.

For low fertile or sandy soils fowl manure or other organic fertilisers can be applied at the rate of 30 to 50 m3 per hectare around two to three weeks before sowing.

Farmers should be aware of the potential dangers of using phosphatic fertilisers with high levels of cadmium.

If cadmium in a fertiliser is in excess of 1 mg/kg, the label or advice note must contain the statement:

"WARNING - use of this product may result in cadmium residues in excess of the Maximum Permissible Concentration (MPC) in plant and animal products and may also result in the accumulation of residues in soils".

DPI is concerned of long-term accumulation of heavy metals in soils and believes that accurate product information assists primary producers to maintain sustainable agricultural practices. Low concentrations of heavy metals generally occur naturally in soils, however, these concentrations occasionally increase due to exposure to industrial sources or containments in fertilizers. Compliance of fertilizer products to regulated standards supports sustainable agricultural systems and helps to reduce the potential for accumulation of heavy metals in soils and plants.

Growers should consult fertiliser suppliers or manufacturers for advice on the cadmium levels of fertilisers they are considering using.

Planting

Frost-prone areas should be avoided earlier and late in the season. Soil temperatures should be above 20°C. Planting can be done either with seeds or seedlings. If seedlings are transplanted the soil should be moist and irrigated as soon as possible afterwards. When direct seeding is used seeds should be planted about 3 cm deep and if soil is cool plant shallow 1.5 to 2.0 cm.

Sowings can extend from early spring to mid summer depending on the chance of frost, soil temperature and the expected length of the growing season.
The plants are generally grown in rows around 1.2 to 1.8m apart and from 50 to 90cm between plants. This gives a population of 9,000 to 11, 000 plants per hectare.

An alternative system is to sow double rows of plants 75cm apart with a pathway of about 1.4 metres between pairs of rows.

Weed control

It is essential to control weeds during the early growth of the crop. Weeds germinating after the zucchini have three or four leaves are not as serious a threat because shade from the crop canopy makes it harder for the weeds to grow.

Some broad leaf weeds can be controlled using as a pre-emergent post planting application. Otherwise hand-weeding and shallow cultivation are necessary to control weeds. Planting into plastic covered beds will greatly with weed control.

Grass weeds may be controlled with selective herbicides, which can be used post emergent.

Pests and diseases

Common pests include cutworms, thrips, leafhoppers, aphids, two spotted mite and pumpkin beetle. While key diseases include powdery mildew and downy mildew.

For descriptions of these pests and diseases see the "Field Identification Guide – Pests, Beneficials, Diseases and Disorders in Cucurbits;" produced by the NSW Department of Primary Industry.

There are chemicals registered for control of these pests and diseases and they are sold under various trade names. Follow the label for directions before use. Contact your chemical supplier or the Australian Pesticides and Veterinary Medicines Authority website will provide you with a current list of registered chemical that can be used on zucchini (www.apvma.gov.au)

Integrated Pest Management

The modern approach to crop protection is to manage pest and diseases so they do not cause economic losses to the crop. This involves crop monitoring so that you know the correct identification of the pest/disease, the level of pest infestation and numbers of beneficials in the crop. Regular crop inspection means you can make informed decisions about when to spray.

Chemical choices should be governed by resistance strategies and the use of soft chemicals where available. Soft chemicals target the pest insect and may not harm some parasites or predators of the pest (beneficial insects). Spray application for pest control should only be carried out when pest levels are high and control is not being achieved. It is also important to destroying crop residues to avoid pest and disease carry over.

Irrigation

Irrigation is generally required and yields will suffer if the crop does not get enough moisture. Other than wilting the most common symptom of uneven or inadequate watering is blossom end rot. This calcium deficiency shows up as sunken dark patches of dry rot at the end of the fruit. Plants will need consistent and even watering to avoid this problem.

Trickle or drip irrigation is increasingly popular and is very effective in maintaining even soil moisture. Both furrow and overhead irrigation will lead to more fungal and mildew problems compared with drip because the foliage is more likely to be wet for extended periods of time.

It is important to schedule irrigation to ensure that the right amount is being applied. Too little and plants will be stressed and yield will suffer and too much can lead to leaching of nutrients and increased risk of disease problems. Irrigation can be scheduled using a range of methods such as measuring soil moisture levels using tensiometers or environscan® (there is a large range of moisture measuring equipment available) or by measuring evaporation.

Harvesting and Storage

If treated well and the weather is favourable harvesting of zucchini can be started 6 weeks after planting and can continue for up to 12 weeks. Fruit needs to be picked at least every second day to maintain the desirable fruit size when the weather is warm. Because of its rapid growth, the fruit soon becomes too large. Constant picking also prevents formation of seed and stimulates further fruit-set.

One plant can produce up to 40 fruit a season if properly cared for. Yields vary from 12 to 18 tonnes per hectare.

The preferred market length of fruit is from 10 to 20 cm. Zucchini are generally marketed in 10-kg cases or packed into the standard black crate if going directly to the supermarket.

The preferred post-harvest conditions for zucchini are storage at 5-10°C and 95% humidity. They are highly sensitive to ethylene and will show signs of chilling injury when stored below 5°C for more than a day.

Further References

"Field Identification Guide – Pests, Beneficials, Diseases and Disorders in Cucurbits;" (2009), Department of Primary Industries, NSW.

Contact/Services available from DPI

Correct diagnosis is essential for effective pest and disease control. A commercial diagnostic service is available at the DPI Knoxfield.

For further information, phone Crop Health Services on (03) 9210 9222 or fax (03) 9800 3521.

For further information on registered chemicals, phone DPI Customer Services Centre on 136 186.

Acknowledgements

This Agriculture Note was developed by Robert Dimsey, Farm Services Victoria in September 1994.
It was revised by Rob Dimsey and Neville Fernando, Farm Services Victoria in June 2011.