Nutrient management recommendations for containerised HNS crops

Most HNS growers use a base fertiliser with controlled release fertiliser (CRF) either added by the growing media manufacturer, or ‘dibbled’ into the growing media at potting to provide enough nutrition for production. 

Trials carried out at ADAS Boxworth during 2020 and 2021 looked at applying lower CRF rates along with liquid feeding.  The aim was to provide enough nutrition during key growth phases while avoiding excess fertiliser at other times and reducing the potential for nutrient loss in run-off water.

The combination of CRF and liquid feed can provide growers with greater control and still meet plant nutrient requirements. Crop safety can be improved by using a lower CRF rate for autumn potting under glass and topping up with liquid feed in the spring as appropriate.

With more control over plant growth growers can optimise productivity and improve quality while reducing crop waste.

Over application may result in nutrients being lost if the run-off from watering/feeding is not collected and could cause pollution.

Use of CRF and liquid feed combinations ensures that any initial immobilisation of ’N’ is offset. It also allows for the steady build up and release from the CRF granules.

Growers could benefit from associated nutrient cost savings.

Recommendations have been developed to lower CRF rates and supplement with liquid feed

Nutrition trials at ADAS Boxworth including Prunus lusitanica ‘Myrtifolia’ and Spiraea arguta

The following CRF / liquid feed combinations below have proven successful over two growing seasons with some plant species producing marketable plants when grown under more than one of the recommended regimes:

 Recommendation 1 – Low CRF, low weekly liquid feed

 CRF: 12-14 month, 1.5 g/L mixed or dibbled at potting

Liquid feed applied once per week at 0.5%:

• 10:52:10 (N:P:K) for four weeks from transplant
• 3:1:3 (N:P:K) from 5 weeks after transplant

Prunus lusitanica ‘Myrtifolia’, Spiraea arguta and Geranium x cantabrigiense ‘Westray’ were successfully produced under this regime. 

This option provides less nutrients than Recommendations 2 and 3, and requires less labour input than Recommendation 3. 

Recommendation 2 – Low CRF, higher weekly liquid feed

CRF: 12-14 month, 1.5 g/L mixed or dibbled at potting

Liquid feed applied once per week at 1.0%:

• 10:52:10 (N:P:K) for four weeks from transplant
• 3:1:3 (N:P:K) from 5 weeks after transplant

This option uses less liquid feed than Recommendation 3, and the lower nutrient content may help to restrict the growth of vigorous species such as Tradescantia.  There is also less risk of excess nutrients being applied. 

Suitable for Spiraea arguta, Geranium x cantabrigiense ‘Westray’ and Tradescantia pallida ‘Purple Sabre’.

Recommendation 3 – Low CRF, low liquid feed at every irrigation

CRF: 12-14 month, 1.5 g/L mixed or dibbled at potting

Liquid feed: applied at each irrigation at 0.5%

• 10:52:10 (N:P:K) for four weeks from transplant
• 3:1:3 (N:P:K) from 5 weeks after transplant

The liquid feed rate for this regime should be adjusted to meet the needs of the crop to prevent excessive application and nutrient loss in run-off water.  Lower feed rates could be used to manage growth of vigorous species such as Tradescantia pallida ‘Purple Sabre’.  However, this option requires more labour input than Recommendations 1 and 2 to produce plants of similar quality.

Suitable for Tradescantia pallida ‘Purple Sabre’.

To select the most effective recommendation for your crop you will need to consider your plant nutrient needs and monitor nutrient supply

CRF and liquid feed rate selection will depend on crop vigour group and longevity. As an example of different vigour groups, the plants used in the nutrition trials were grouped as below:

The longevity of the CRF should be selected to match the crop, for example a 12+ month product for overwintered crops, or an 8+ month product for a single season crop (various longevities are available). If combining CRF with liquid feed, the CRF rate should be reduced to avoid excessive nutrients being applied. Beyond this, some crops are more sensitive than others to EC, and CRF rates should be adjusted to account for this – see below for vigour groups.

Vigour groups for CRF rates:

Crop nutrition monitoring informs nutrient supply management and helps with early identification and correction of deficiency or toxicity symptoms.

Irrigation water nutrients and bicarbonate.  Laboratory analysis (including bicarbonate) should be carried out twice per year. Liquid feed applications should be adjusted to account for any nutrients in the irrigation water.  AHDB Factsheet 15/06 provides information on irrigation water quality, including suggested maximum EC and nutrient levels for crop groups.

Growing medium. Laboratory analysis for available nutrients for key / high value crops should be carried out through the growing season (e.g. initial unused, mid-summer, early autumn and late winter).  Where CRFs are used, the late winter analysis should be on both ground and unground samples – the latter will provide information on the nutrition remaining in the CRF.  AHDB Factsheets 10/16 and 05/19 provide information on how to sample growing media and interpretation of analysis results.

Store a sample of unused growing media in a cool, dark storeroom or cupboard for later analysis should problems arise within the crop. 

Leaf tissue analysis. Tissue analysis should be used to diagnose nutrient disorders, sampling from plants with suspected nutritional problems and unaffected plants.  There are limited published standard values for specific crops and cultivars, but AHDB Factsheet 10/16 provides a summary of nutrient values from a range of woody plant species as a general guide. 

The content of this webpage was authored for AHDB by:

Jill England and David Talbot, ADAS Horticulture, Susie Holmes, Susie Holmes Consulting Ltd, Neil Bragg, Substrate Associates Ltd. and John Adlam, Dove Associates Ltd.