Kildalton College

Piltown, Co.

Kilkenny

Helping people grow careers in horticulture for over 50 years

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QQI Level 5 Certificate in Horticulture

QQI Level 6 Advanced Certificate in Horticulture

QQI Level 7 Bachelor of Science in Horticulture (in conjunction with South East Technological University)

Part-time Component Awards at Levels 5 & 6

QQI Level 6 Higher Certificate in Sportsturf Management - Apprenticeship

Kildalton College has an extensive horticultural unit for student training, including a commercial nursery, fruit and vegetable production unit, protected crops and sportsturf units, as well as 16 hectares of established gardens and woodlands.

For further information:

Email: Kildalton.college@teagasc.ie

Website:www.teagasc.ie/education/teagasc-colleges/kildalton/horticulture

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Telephone: 051 644407 for her experiment was spent coffee grounds, a well-known viable addition to compost. Coffee contains high amounts of nitrogen and other beneficial compounds that can improve the nutrient profile and texture of compost. Ground coffee is a rich source of nitrogen, which is essential for plant growth. In addition to nitrogen, coffee also contains other beneficial compounds such as potassium, magnesium and calcium.

According to a study by Ana Cervera-Mata called ‘Spent coffee grounds by-products and their influence on soil C-N dynamics’ – published in 2022 in the Journal of Environmental Management – increasing N, P, K content enhances structural stability of soil aggregates, water-holding capacity, soil hydrophobicity and decreasing bulk density.

Given that improving water-holding capacity of novel composts is a key issue with bark and wood fibre composts, the water-holding capacity of coffee grounds is significant.

The use of coffee grounds has other environmental benefits through diverting coffee waste from landfill. The International Coffee Organisation estimated global coffee production in 2018 at 159.66 million bags, and that 1.4 billion cups of coffee are prepared each day.

For the purposes of Zoe’s research, the chosen ground coffee was Coffea arabica medium roast coffee from McCabe's Coffee on UCD campus.

The third locally-sourced ingredient for Zoe’s novel compost mix was common lawn moss (Rhytidiadelphus squarrosus), a readily-available species from most Irish lawns that is easily harvested and very renewable.

As with coffee, moss was added to assist with texture and to help with water retention.

The Experiment And Its Results

The novel compost mixes were combined by hand and placed into one litre, 100 per cent compostable bags within the Joraform Compost Tumbler JK270 ‘Big Pig’. This was turned every seven days during the active composting period.

As we write, the novel mixes continue to compost. However, the experiment is sufficiently advanced to be able to test for pH. Tests were carried out to determine and compare the pH of the novel composts that Zoe created in comparison to current commercial peat composts and peat-free alternatives.

extremely high or low in a compost, the plants growing can suffer either from deficiency or toxicity, so getting the pH balance right of any new compost is key.

Mixing materials such as coffee and moss – which have high pH – with the lower pH material of oak shavings, resulted in lowering the pH. Coffee and oak shavings combined had a pH of 5.6, a move in the right direction. While the figure is nowhere near the lows of solely peat-based composts (4.5-5), it is comparable to current peat alternatives with their pH of 5.7. The coffee, moss and oak mix had a higher pH of 6.

Initial lab results are in. To give an idea of the range of values: Shamrock Multi-Purpose Compost had an average pH of 4.5; current peat alternatives had an average of 5.7; and at the higher end of the scale, both coffee and moss individually had a pH of 5.9. Most of the wood-fibre alternative composts on the market had a pH in the range of 5.7.

PH is very relevant to nutrient-uptake for plants. When it’s

Plant Perspectives

What does all this mean to a growing plant? The mix with coffee and oak was the most successful, with 25 per cent cress seed germination after 5 days, compared to standard peat compost at 70 per cent.

The results of the research show that we still have a long way to travel in developing alternative composts suited to industry. While there is no quick fix on this journey towards sustainability, there are plenty more novel and fun local materials to explore as potential substitutes for peat compost.

Waste food products like tea – which in Ireland we drink by the gallon – and potato peel (which we create a lot of), alongside seaweeds and invasive species, are waiting to be analysed for their potential as compost materials.

So it’s back to the lab for us! ✽

Zoe Valentine has just completed her honours degree with UCD Horticulture. This article is based on Zoe’s research, which was led and supervised by Noeleen Smyth, Assistant Professor in Environmental Horticulture at UCD.