There’s a new five-year strategy in place to promote plant biosecurity in the UK, but what does this really mean, and why should we gardeners pay attention? Chief plant health officer Nicola Spence tells Gardens Illustrated editor Stephanie Mahon why you really shouldn’t be sneaking plants back from your holidays or sharing rare plants around your garden club, plus why that hedging pack deal online that looks too good to be true probably is, and how designer show gardens might look a bit different in the future.

Why should we be concerned about plant biosecurity at all in the UK?

First of all, it’s important to understand what’s at risk - the value to society of our plants and trees - and in the strategy, we’ve monetized that to the tune of more than £15 billion annually. And that’s not just about selling plants. It’s about how we value them socially, and the kind of environmental contribution they make. They are an incredibly important asset. And of course, there’s all the things that you can’t monetize about how we feel about plants and trees, how they enhance our lives, as well as the environment. It’s why I studied botany when I was 18, because I felt that the world cannot survive without plants.

We need to get people to understand that plants and trees can also get sick from pests and diseases, and we all have a responsibility to protect them. So this strategy is very much about not just what government action will be in terms of regulation legislation, scanning for threats and taking action, but it’s also about how society and individuals can do their bit to protect plants and trees, and enhance their lives and the wider environment.

We need to get people to understand that plants and trees can also get sick… and we all have a responsibility to protect them

It’s been about 10 years since ash dieback was discovered in the UK. What other things should we be concerned about and looking out for?

We do have a UK plant health risk register where we catalogue every threat, and it’s quite a big read - it’s got 1,400 threats on it. One to look out for is the emerald ash borer. We’re seeing the effects of ash dieback with some trees quite badly affected but also some trees that look quite healthy - they’re the tolerant ones. We’re expecting these tolerant trees to survive dieback, but they are at risk now from the emerald ash borer. It is a jewel beetle, a very beautiful iridescent green, but it’s absolutely deadly to ash trees, a major threat, and one that we absolutely must keep out. The primary pathway is firewood, and that’s very strictly regulated, but one question is why are we importing firewood, when there is this risk? There’s plenty of wood available - actually the ash dieback is creating lots of firewood available for people to purchase locally.

The second thing to mention is Xylella fastidiosa, a bacterial plant disease that has devastated olives in Italy and is established in several parts of Europe, including France, Spain, Italy, Portugal and the islands of the Mediterranean. It’s got a very wide host range, so it can infect more than 500 different plants. That makes it very difficult to manage.

We did an investigation and found more than 10 different viruses. Some were completely new to science and had never been described before

The government is very strictly regulating any host plants of Xylella, with certain plants being prohibited from many parts of the world. The kinds of plants typically that are high risk are things like olives, oleander, rosemary and lavender - plants that most UK gardeners would recognise. So the advice is to be very, very cautious about where you buy those plants. Buy them from a reputable supplier. Ask questions about where they’ve come from. When I go to a garden centre or a supermarket, I’m always trawling over the labels. I’m interested to know where the product is from. Does it have a plant passport? Has it got the right label? It would be great if people were more aware of that.

Olive trees cut down because of Xylella fastidiosa
© Getty

Are gardeners going to see any major differences due to this strategy when they buy plants at a nursery or garden centre, or visit open gardens?

They are going to see more visible information about plant health and biosecurity. Hopefully they will see that their local garden centre has Plant Healthy accreditation and they might see some labelling and some sort of communications about that. When they’re buying online, they’ll see that businesses like Crocus are accredited – a bit like the Red Tractor Mark or the Organic Mark.

Everyone thinks, oh, how could it do harm, it’s just me and my little garden

Gardeners might find that some things they want are not available now. I would hope that the nursery or a gardening publication might help explain why that’s the case. A few years ago, the September bush [Polygala myrtifolia] was everywhere in retail and although it’s very pretty, it is one of the highest risk hosts, an absolute nightmare. We were regulating it very, very tightly and the messaging around it was quite negative, and eventually everyone just stopped selling it, so that was a great outcome as far as we were concerned. Some gardeners might have been disappointed but there’s always something else to try. Just don’t go out of your way to fill your garden with the riskiest things.

Would you say there’s a situation now a bit like the illegal sale of pets on Facebook and other social media? People can buy plants online, not just from reputable suppliers, but from anyone and where they’re buying it from may not be legit.

Yes, just because it’s for sale on the internet doesn’t mean to say it’s legal or desirable. We are investing more resource into our internet trading unit to give us more capacity. We do lots of scraping the internet using investigative tools similar to the police to search on keywords and we take sales down if we find that illegal materials are being traded, but it is a constant challenge.

If something really looks too good to be true, often it is. Last year, for example, we intercepted 1,800 bareroot fruit trees in individual boxes that were going to people’s homes.

Just because it’s for sale on the internet doesn’t mean to say it’s legal or desirable

They had obviously purchased them online through an advert. We seized the whole lot and sent them back where they came from, because none of them had any phytosanitary certification, and fruit trees are very high risk. They can harbour hundreds of different pests. And they’re going into people’s gardens and staying there for years and years. So there were lots of disappointed customers. The supplier thought they might get away with it, and they didn’t, but we’re seeing more and more of that kind of thing.

You advise gardeners not to bring back plants and seeds from abroad, but how much of a risk is this really, in the scheme of things? Isn’t it more likely that it is large groups of plants being transported in the trade that pose a greater threat?

It’s good question. Obviously, the volumes are with the trade, but we’ve got evidence which shows that some pests have been introduced through that informal network of people that like to move their personal plants around or take cuttings. For example, the fuchsia gall mite was introduced via people on holiday in France, who brought cuttings back, initially to Jersey, and then those plants were shared and distributed through the south of England, and it’s a pest that’s now established and it’s a real problem.

It’s all of our responsibility not to bring back cuttings or seeds from our holidays. You can imagine, with something like Xylella, a rosemary or lavender cutting from a holiday home in Spain, it actually could be lethal. So ‘Don’t risk it’ is one of our public information campaigns.

Also, people like to share plants and seeds within gardening clubs, and again, if you’re going to do that, you want to be certain what the origin of that material is and you’re not inadvertently spreading diseases. We had somebody a couple of years ago who was sharing a vegetable called oca, which is an Andean tuber, and they were distributing it and selling it to a kind of smallholder network. We found it through our internet trading unit and traced it back to an individual, and visited their premises where they were growing this crop. It was very obvious immediately that there was a problem. It was full of viruses - you could see it on the leaves – and once we did an investigation with a full genome sequence analysis of the plants, we found more than 10 different viruses, some of which are a threat to the potato industry. Some were completely new to science and had never been described before! We took swift action and destroyed the crop and took all the sales down, and then introduced legislation to make sure that that trade is completely prohibited.

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One well-known designer was horrified to discover that they had an illegal plant… Somebody had added it at the last minute without realising it’s not allowed at Chelsea

We know everyone thinks, oh, how could it do harm, it’s just me and my little garden. I talk a lot to gardening groups, and I don’t want to fill them with fear and dread, but I do, because they just don’t think about all those different pathways.

Gardening clubs get cross with us that we’re regulating things and they can no longer get the seeds they used to, or when they go on their gardening holidays, they can’t bring back things they used to without a phytosanitary certificate that they’ve got to pay for - but actually we are protecting the value of our plants and trees.

Xylella might be brought in on lavender, for example, but actually the real risk is to our oak trees, because you can get that movement into the wider environment. So the more we can get people to understand that and care about it, then I think we will have some positive outcomes.

How will the new plant health strategy affect something like the show gardens at the RHS Chelsea Flower Show, where designers often use mature trees imported from Europe to make a real statement? What are the designers going to do now?

We work closely with the RHS, and they have a biosecurity strategy and policy themselves. It has been the case for a couple of years now that if you want to take a mature tree to Chelsea, it’s got to have been in the UK for at least a year, and some species they don’t allow, such as olive. They’re trying to manage not just the biosecurity of the show, but also aligning it with the national strategy.

I know it’s challenging, but I think it just requires a bit of planning, and I know that’s difficult because these gardens are designed and planned and specified, and you have to be confident that you can get what you want if it’s an important part of the design. So I think my message to the designers would be to work closely with the RHS, understand what some of the high risk material is, and don’t specify it, or look for a suitable alternative. Work with many of the nurseries that actually have this material already here.

Gardeners might find that some things they want are not available now

Everyone wants the perfect tree that they’ve seen growing in a field in, say, Italy, the one that they tagged etc… but, I mean, just imagine a Xylella outbreak at Chelsea - it would be devastating.
It’s why I send inspectors to Chelsea for two weeks during the build-up and they look at everything. They remove things if they shouldn’t be there. In fact, one well-known designer was horrified to discover that they had an illegal plant on one of the trolleys. Somebody had added it at the last minute from the nursery without realising it’s not allowed at Chelsea, and it was spotted and removed, and they were sort of reprimanded. But it showed that the system works.

Designers just need to work within this new biosecurity framework and I think that’s best for everyone. Because if Chelsea full of high risk prohibited material, then that’s not good. So let’s work together and have a fantastic Chelsea, but make it more sustainable by being more secure.

Read the news on Great Britain's five year biosecurity plan


Stephanie Mahon, Editor of Gardens Illustrated
Stephanie MahonEditor, Gardens Illustrated

Stephanie Mahon is Editor of Gardens Illustrated. She is a multi-award winning garden editor, writer and author. Her book Wild Gardens, which is the GMG Garden Book of the Year, is out now.