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Developing sustainable growing media alternatives for soft-fruit propagation

Change was certainly in the air when growers visited EU Plants on the Hampshire/Berkshire border on a blustery day in September. In addition to the change of season, those who attended AHDB Horticulture’s ‘Growing Media Developments in Soft Fruit Propagation’ event were given a glimpse of a more sustainable future in which the UK’s soft fruit sector need not heavily rely on one type of growing media. Rachel Anderson reports.

Initially gathering in The Golden Potin the pretty village of Eversley, Hampshire, attendees first heard from ADAS horticulture consultant Chloe Whiteside. She updated them on the latest results of the soft-fruit trials that are being carried out as part of AHDB Horticulture’s project CP 138: ‘Transition to Responsibly Sourced Growing Media (RSGM) in the UK’.

As growers may be aware, professional horticulturalists have until 2030 to achieve a voluntary target of phasing out peat in commercial production. The five-year CP:138 project, which is funded by Defra, AHDB, growing media manufacturers including Bulrush, Sinclair, ICL, and Bord na Móna, and growers, is largely focusing on trialling, and evaluating the performance of peat-free growing media blends.

Its aim is to construct a model that will produce desired growing media mixes at least cost, and to help growing media manufacturers bring new peat-free or peat-reduced blends to market quickly. Different combinations of coir, bark, wood-fibre and green compost are being trialled. With its widespread use of coir, the UK soft-fruit industry obviously relies less on peat than some other horticulture sectors, so both coir-reduced and coir-free blends are being tested in the soft-fruit trials. These experiments, revealed Chloe, began in 2016 at New Farm Produce in Staffordshire. Then, nine commercially-available growing media treatments (with coir as the control) were trialled on bare-root and tray-planted Malling Centenary strawberries. After analysing the yields from this experiment, the results showed that “with optimised irrigation and nutrition there is potential for coir-free to work just as well as coir.” A similar trial in 2017 also had positive results, as some of the trial blends produced yields that were greater than the control. 

To cover all the sector, the next phase saw the research team “go backwards a little” by focusing on the initial stages of commercial fruit production – namely propagation. This saw both a raspberry and a strawberry trial set up in 2017 at EU Plants’ various farms. Glen Ample and Maravilla raspberries were raised from cuttings in 100% coir (control), three peat-free prototype blends, and one coir-free blend. Similarly, young Elsanta strawberry plants were raised in 100% coir (control), three peat-free prototype blends, and one coir-free blend. There were some interesting results: for example, in the strawberry trial, the plant quality was marginally reduced in the control coir-grown plants.

EU Plants, Church Farm West

The latest part of this experiment has seen a second-generation of prototype growing media blends, developed using a comprehensive data model that has characterised and compared the physical properties of all the raw materials, used in more raspberry and strawberry trials at EU Plants. It was these trials that attendees visited, including the raspberry propagation trial at EU Plants’ Church Farm West in Eversley. There, the group could see Maravilla raspberry plants in two-litre pots being grown in 100% coir, four peat-free prototype blends, and one coir-free blend. A Glen Ample trial has been set up simultaneously at EU Plants’ site at Millets Farm, Oxfordshire. Chloe said: “In these early stages of the trial we haven’t really seen any difference in terms of how the plants are growing.”

After the visitors had looked around the raspberry trial, the firm’s owner Slavey Slavchev took the opportunity to talk about his business. Like most success stories, it has taken years of hard graft and very few holidays to build the firm up to the enterprise it is now. The hard work has evidently paid off as EU Plants supplies soft-fruit plants to some of the UK and Europe’s top berry producers. Slavey revealed that he started his journey several decades ago: “It all started 20 years ago with bare root Glen Ample which, for a lot of growers, is still the best product.” Some 13 years ago he rented land at Millets Farm and then, seven years ago, Slavey bought his own farm – nearby Manor Farm in Finchampstead, Berkshire and he added, “Three years ago we then added this farm, Church Farm West.”

Slavey revealed that both his farms were just pastureland without any infrastructure in place when he purchased them. This fact was difficult to process, given the thousands of plants already growing in his custom-made wire support systems. He pointed out that, in addition to his cleverly-designed supports, for which he claims many benefits, including causing less damage to the plants than string, all the canes are grown in coir in pots. “We’ve been using 100% coir for four years. We have learned now how to work with it, for even the finest of jobs.”

He added: “We are trying to grow floricanes from the primocanes, which is extremely difficult. The plants want to flower this autumn and we want to prevent them from flowering.” The group learnt how Slavey’s entire production is made from cuttings that are rooted for six weeks before being transplanted into pots. “The same goes for strawberries,” he said. He revealed that, for Church Farm West, he and his team will wait for all the raspberry canes to become dormant and for their leaves to become “well senesced” before they are packed, still in their pots, into big boxes and then chilled. “By the end of January, the field will be completely empty until June of next year.” The raspberry plants are chilled at a temperature of -1C to -1.5C and, said Slavey, they need to be chilled quickly to avoid incidences of brown root rot.

Regarding cold storage, ADAS horticulture consultant Janet Allen reported that the soft-fruit industry has, because of this year’s exceptionally hot weather, experienced some problems with previously cold-stored plants. She said: “They were probably delivered before the root ball had completely defrosted and planted very quickly into black pots or troughs under tunnels, and in temperatures that we’re not normally used to in the UK (30C or more).” Janet speculated that the roots had possibly ‘cooked’. “A lot of the plants that went out bare root and were planted in this ground did not have this problem, which suggests to me that the substrates were really hot. Raspberries are adapted to the cool temperate conditions of woodland glades.”

The visitors discussed the possibility of using light-coloured pots, or that such plants should be initially kept in the shade. AHDB Horticulture’s Knowledge Exchange Manager for fruit, Scott Raffle, recalled that a previous James Hutton Institute research project has shown that post-storage acclimatisation is key.

Slavey revealed that the hot summer has created a good growing year for EU Plants, with “a lot of growing degrees. Hopefully that will be reflected in next year’s fruit, but we’ve prepared an extra borehole for next year in case we get a drought again, as we had to watch water levels at one stage.”

He mentioned that EU Plants grows 3.5 million raspberry plants per year; the majority of these are Maravilla and 1.0 million of them are Diamond Jubilee, but he also grows a small amount of Glen Ample and Tulameen. In addition to the 3.5 million raspberries plants, an impressive 3.3 million strawberry plants and 1.0 million blackberry plants are also grown. Slavey said: “13 years ago we grew 100% speculatively, but now we are 95% sold out. Times have changed, and we are forced to grow to order.”

EU Plants, Manor Farm

Following lunch at The Golden Pot, the group spent the afternoon at Manor Farm where Slavey pointed out another sign of the times – his dwindling Elsanta production. Nowadays, the farm’s strawberry plant propagation largely comprises Malling Centenary.

Slavey impressed some members of the group when he explained that the mother-plant material is grown out for a couple of years, and its fruit is meticulously inspected before it is used for propagation, as genetic mutations and variations are surprisingly common. Slavey said: “Fruit testing is probably one of the most important things for us. Only the fruit can tell you the full story. We’ve been doing this for seven years.”

At Manor Farm the group visited the CP 138 project’s strawberry trial, featuring the second-generation prototype blends. Malling Centenary is being grown in both trays and pots in either 100% coir, four coir-reduced blends and one coir-free blend. These plants are being assessed at five-week intervals for quality, height and root development and, before winter cold storage, crown size. “There’s not much to see in terms of differences, which may seem slightly boring, but for this project it’s looking good. We are not seeing huge differences between coir and coir-free.”

In 2019 both the raspberry and strawberry plants are moving north to a new home at New Farm Produce. Chloe said: “We will be able to collect yields next year, so that will be interesting to see.” The plants will be grown in standard coir and the blends they’ve been created in.

The effect of cold-storage of long cane raspberries on phytophthora root rot

With the number of available plant protection protects dwindling, an AHDB research project (SF 158) is looking to help the industry find alternative ways of preventing young plants from succumbing to phytophthora root rot. In her presentation to the group, ADAS plant pathologist Ruth D’urban Jackson explained that the project is examining two things – cold storage and the potential of biofungicides – “to see if we can hit this disease on the head.”

The trial, which started in autumn 2017, saw half the plants put in cold-storage over winter and the other half left out in the field. In both groups of plants, some were treated in the autumn and the rest were treated in the spring. The treatment contained a combination of the biofungicides Prestop and Serenade and the conventional fungicide Paraat.

In spring 2018, the plants were all moved to ADAS’ Boxworth site, inoculated with the phytophthora pathogen, and then monitored until June. As is often the case with experiments, the results yielded “no big conclusions.” Ruth said: “Even though we saw that there was higher rotting in the roots that were ambient [left in the field], overall, in the cane assessment we didn’t have particularly massive differences between the ambient and the cold. It was more about when the treatments were applied. There are lower incidences of floricane wilting in autumn-treated than spring-treated, and primocane were the same.”

Ruth added: “It’s quite a complex story – cold storage has its place; we just need to figure out the best way to be treating the plants and, when they come out of cold storage, depending on the year and the temperatures, you need to keep quite a close eye on those plants to make sure that you’re working on the entire story rather than just saying: ‘they are in the cold store and they’ll be protected from now on.’”