This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Carrot juice production had for a long time been the lowest value sector in the Australian carrot industry. With global interest in functional foods, the availability of high anthocyanin lines, presented the industry with a real opportunity to regain some profitability.

Considerable difficulty in growing satisfactory commercial “black” carrot crops that were both acceptable to processors and sufficiently profitable for growers, had been a major obstacle to growing this fledgling industry both locally and internationally.

This project addressed a broad range of black carrot production issues. This was achieved by evaluating approximately 30 individual field trials and commercial crops, mainly in the south-eastern Australia (SA Mallee, Mildura, Tasmania, and Southern Victoria) as well as prospective northern production areas (Darwin, Katherine, Bowen). Key lines of enquiry and findings included:

• Extreme vernalization sensitivity of the key variety at the time. Any exposure to average day temperatures of about 16°C or less in the first 3-4 weeks after planting resulted in unacceptable levels of “early” bolting.
  • Following from this, the creation of a basic model for growers to determine the likelihood of crops bolting when planted at different times of the year, based on historic or live weather data.
  • Identification of both traditional and prospective new production regions in Australia to allow year round supply.

Essential nutritional requirements for black carrots were found to be similar to conventional high carotene carrots on a rate per ha basis but higher on a rate per ton of harvestable product.

Attempts to divert plant resources away from vigorous canopy production into more useful carrot production, by manipulating nitrogen inputs, irrigation, plant density or using chemical growth regulators were not found to be broadly effective.

The plant spacing that maximised harvestable yield and average carrot weights while minimising undersize (unharvestable) yield was 40-50mm in most situations.

The importance of heat was a key cause of poor germination and plant establishment as well as being the likely cause of seedling decline.

Higher frequencies of forking were associated with extreme heat at or soon after planting.
Black carrots were not found to be any more susceptible to the more common damping off pathogens than conventional high carotene carrots, nor did any of these prove to be the most important contributing factors to poor crop establishment. Fungicides applied as soil drenches did not significantly improve the harvest quality or yield for the processing market (as disease was not found to be the major cause of harvest quality or yield losses).

Black carrot tolerance to the herbicides linuron and prometryn was similar to conventional high carotene carrot lines.

The larger canopies and rapid growth rate of black carrots indicated higher water requirements than for conventional orange carrots, particularly during early growth to maximise yield and quality.

While other high anthocyanin lines were evaluated, the variety Excelfresh LX3632 remained the current industry standard.

An Agronomic Guide to growing black carrots in Australia based on best information at the time was produced.