Episode 137: Water-wise Gardening with Janet Manning

Welcome to this week’s episode, where I’m talking water-wise gardening with Janet Manning. Janet undertook a three year project with the RHS and Cranfield University where she looked at strategies and techniques currently available to gardeners to help them both conserve and manage water in a way that reduces waste and protects the environment. We talk about why there’s a need to be water-wise in wet countries like the UK, what we can do to help and why gardens are an important part of the bigger environmental picture.

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What we cover

Janet’s work with Cranfield University and the RHS

How we gardeners can conserve water in our gardens

How we can contribute towards rainwater management

Drought tolerant plants

The fabled moist, well-drained soil!

Using swales and hugelkultur beds

Long term meteorological predictions

About Janet Manning

Janet has just completed a three year water management knowledge transfer partnership between Cranfield University and the RHS. As a graduate of Cranfield with an MSc in process engineering, and after a 17 year career as a scientist in the water industry, she followed her passion for the natural environment into horticulture where she worked on a production nursery producing hardy ornamentals. Having worked ‘both ends of the hose’ she was well placed to take up the role at the RHS as the first garden water scientist. She has contributed to the water neutral targets set within the RHS’s new sustainability strategy and has written the first water road map for Wisley as a plan implement the strategy. A gardener since she was big enough to pick up a trowel, the combination of practical gardening experience and scientific knowledge, she has recently left the Environmental Horticulture Team at Wisley but with a legacy that will continue through the sustainability strategy.



RHS advice for water management

RHS Neutral Water Targets

Meeting our future water needs: a national framework for water resources


Janet Manning 0:00

Yes, absolutely. So I’ve just finished the KTP project with Cranfield and the RHS. KTP stands for knowledge transfer partnership. So it was all about transferring the academic knowledge from Cranfield to help the RHS, develop their water management planning. And I think we’ve fairly successfully done that. But we’ve also done an awful lot to actually transfer that knowledge out to the gardening public as well. And the most recent, you know, the combination of the project, if you like, was two main things was the website called Mains To Rains, which helps gardeners understand how they can switch to using much more rainwater in their gardens. It’s free, and it falls out of the sky regularly, as we all know, in England, so, you know, it’s it’s there for us to use. And it’s much more sensible to use that than the mains water, lots of ideas on that website. And also to display all of those features to the visitors to the Chelsea Flower Show, we took that display to Chelsea in September this year. So yeah, that was sort of the combination of what gardeners in general would have seen, but there was an awful lot more going on in the background at the RHS themselves.


Sarah Wilson 1:16

What’s your background? How did you get involved with the project?


Janet Manning 1:20

Well, that’s an interesting one. So I’ve always gardened since I was big enough to pick up a, you know, a small spade or shovel, but my first career was in water industry. So I spent 17 years working in Wessex water, as a scientist, helping to keep all the pollutants that we often hear about out of the water. I had three children. So that sort of put a stop to that career really. And I decided that once the children were growing up, I was going to just enjoy doing some gardening and I went to work at my local garden centre, which fitted perfectly around the kids. That was a small independently run garden centre. And it was lovely. It was great five years I spent there actually watering plants and actually selling them to the public. But then they decided to retire and sell the nursery. And so I started looking around for other work and up pops this advert for a scientist, working with Cranfield University, working in the RHS, to help gardeners use water better in the gardens. And so I thought I tick enough boxes for that for an interview, maybe I get a free day out. I never thought for one minute that I would actually get the job. But there we go.


Sarah Wilson 2:44

Wow. Well, what a result. You know, we talk about conserving watering gardens, it is an ongoing conversation for gardeners, what are the main things that gardeners can do to conserve water within their their own back gardens?


Janet Manning 3:05

Well, this is where I’ve tried to sort of change the language slightly, we talk a lot about saving water. And I’m sure we can, but it’s not quite as simple as just saving water, it’s about managing water. If we think about the way the climate is changing, we’re going to see more extremes. So we’re going to see longer, hotter, dry spells, we’re also going to see really longer, heavier rainfall, that’s going to cause flooding, more surface water. And that in itself can cause equally as many problems. And so it’s trying to manage that situation. So you know, it, it doesn’t take much when you think about things in a circle, you can just hang on to some of that excess water when it’s about and then use it during those dry spells. Everybody benefits. So it’s not necessarily about just saving water, although I’m sure we all can it’s about managing the water that’s there, when it is there, so that you can use it when it’s not there. But yes, there’s loads of things that you can do in your own garden. The most instant and obvious thing that everybody thinks sold is water butts. Great, you know, if you’re not using one, or if you’ve got one and you’re not using one, which is even worse, then please do use your water butts. They help to collect all the rain that comes off of your roof which is more than enough to help with an awful lot of gardening needs. And there’s lots of ways you can add water butts to garden. You don’t necessarily have to put them in the spot where the downpipe comes down off the roof. There’s other ways that you can move water around the garden using syphons. So yeah, there’s loads of different ways.


Sarah Wilson 4:51

Yeah, so actually conserving water was the first part of my question. The second bit was how can we garden that contributes towards rainwater management. So obviously, using water butts is one of the things. And I’m sure, like you say there are so many things that can be done, what are the most important ones in your opinion that people can do to manage water more effectively.


Janet Manning 5:15

So I think a lot of people sort of forget about is the if you think about the natural world, the natural world doesn’t have water butts. But it does have deep organic, healthy soils. And that’s where we can store lots and lots of water. So by adding organic matter to your soils by not digging it, but keeping that open structure through, you know, having healthy, healthy soils with lots of organic matter in, then that helps to retain the rain, when it does come. It helps the rain infiltrate down through the soil that recharges the groundwater and the plants growing in it, they also then actually take away the nutrients from it. So the water that does reach the groundwater is actually pure as well without those nutrients added.


Sarah Wilson 6:03

And is this what is known as this fabled thing called moist, well drained soil, which is referenced on probably every page of the RHS website where they mentioned plants and plant requirements. Is that what that is? Is that what you’re talking about there? The soil or the organic matter in it?


Janet Manning 6:20

I’m glad you brought that up. Because that was one of my, yeah, I spent years as a amateur garden thinking, what on earth does moist, but well drained soil really mean? And that really bugged me right from the beginning. That doesn’t tell me anything, you know, moist means it’s wet, well drained, means it’s dry. What does that mean? So let me try and explain that one in a slightly better way. When you want roots to grow in your soil, they need water, but they also need oxygen. So like every other living thing, the roots need oxygen to respire. And so you’ve got to have that balanced mix of water and oxygen in your soil. And to get that you need those open air spaces, you need the pores in the soil. And what happens is that when you’ve got healthy soils with lots of invertebrates, and things like earthworms, and springtails, and wood lice, and all things running through it, they create those little pore structures, the bacteria themselves that actually live in the soil, they also exude what I call bacterial poo. And it’s like a natural swell gel. And it creates the sticky sort of glue that helps to glue the crumbs of the soil together, which then opens the soil up. But when you’ve got those air spaces, but you’ve also got all those lovely big surfaces on the soil particles, then the soil particles themselves can be capturing a layer of water, but then you’ve got those air spaces between them. And then you’ve got a really great environment for the roots to grow, that can get all the water they need, and all the oxygen that they need as well.


Sarah Wilson 8:08

Perfect. Well, that does clear up something that baffles I think probably most people. So thank you for that. And the other thing that is perhaps, you know, potentially was a bit daft I think, about 15 years ago, maybe there was this big push to get everybody to grow drought tolerant plants, because we were all heading towards this Mediterranean climate, due to climate change. And what happened was there was a particularly strong push for maybe a year or two. And then a year after that we had really awful flooding. And I think everybody lost their plants. So have you looked into much into drought tolerant plants in as part of your research? Do you think there’s a place for them still in this country?


Janet Manning 8:51

Yeah, I’ve not done an awful lot, actually directly with plants are very much focused on water and water management. So specific plants? No, haven’t done a lot with it. But yeah, I quite understand what you’re what you’re talking about. And it does frustrate me that as soon as you mentioned, we’re going to do something about water and water management. Somebody says, oh, yeah, we’ll grow some drought tolerant plants. I think that’s not the answer. So I get very frustrated looking at gardens full of gravel and succulents thinking, the first time you get a really wet winter, you’re going to lose the lot. And the first time you get a really hot heatwave dry spell, then that garden is going to be unbearably hot and uncomfortable for even the people on the plants in it. So drought tolerant plants are not the answer. The clue is in the name. We’re having climate change, the climate is changing. We’re not changing to a Mediterranean climate will change into something that’s probably not been seen anywhere on the planet. It’s all different everywhere. We’re going to explore once the Mediterranean in one season and we’re going to experience You know, horrendous floods in the next season. And there’s, you know, there’s no getting away from that. And so what we’ve got to get is resilient planting, not drought tolerant, not water resistant, we’ve got to get resilient planting. And that means lots of layers of design ideas, changing the typography in your garden, so that when you when you have these dry spells, you can create some shade, shade immediately helps to lower the temperature, when you have really, you know, lots of water around, you can change topography so that surface water can be collected and attenuated somewhere. Or you can drain it away to somewhere where it can be safely attenuated. So there’s lots of ways of thinking about it. And I think you’ve got to think about extremes. Both drought and flood, not just not just heat waves. Yeah.


Sarah Wilson 10:55

So in permaculture, the practitioners often talk about using swales, have you studied their effectiveness at all? And are they appropriate in a smaller garden?


Janet Manning 11:04

Yes, absolutely. I mean, I live on a very steep sloping garden, the house was actually built on what was a very small quarry. So we have no sub soil at all, we have really steep sided hill, the garden has been terraced. So it’s actually really difficult for me to keep any water here. But what I’ve done is used swales at the base of each terrace. So any water that does start to run down the hill is immediately caught at the top of the terrace so that it is then encouraged to go downwards through the depths of the terrace wall, just inside the wall. So it just helps to slow that rainfall down, it helps to slow down the surface water and encourage it down into the ground. So that’s what we really want is to encourage the water to get into the ground to infiltrate through the top layer of the top soils and, and get further down into the groundwork. It does less harm for everything that has to live on the surface for one thing, it encourages the water to get down into to the groundwater. And that’s absolutely where the roots need it anyway. So yeah, I would, you know, swales are great. And it doesn’t have to be specifically a swale, it can just be thinking about the levels in your garden and adjusting them so that water is retained better.


Sarah Wilson 12:36

And have you done any research into things like hugulkulture culture beds, so you obviously have the wood in the ground? The wood supposedly absorbs a lot of water and holds it there? Is there any research on the effectiveness of those?


Janet Manning 12:50

To be honest, I’ve actually done very little new research. So I did do some trials in my first year. Unfortunately, with COVID, as it was, that put a stop to an awful lot of the practical work. Because you know, there was a time when we couldn’t even get into Wisley, we were all working from home. So the research has been pretty limited. But there’s an awful lot of research out there that’s already published. And all we’ve done really as gathered it all together in one place. So hugulkulture holds on to water underneath the soil by using the wood. After all, you know, wood is designed to take water up through the xylem. You know, that’s what it is, isn’t it, it’s lots of little tiny water pipes held within the stem of that tree. And so it does, it holds water really well. And that’s a natural way of doing it. But there’s lots of containerized systems that are available that actually just have a reservoir in the bottom of them, which then means that there’s a wicking system, usually and it can be a bit of capillary matting, that can be the actual soil itself, that acts as a wick to then take that water back up into the root zone. And I did look at those in one of my trials and they worked really well. There’s a couple of advantages to them is that because you’re storing the water underground, then it is protected from the surface evaporation so you do tend to lose quite a bit of water from surface evaporation topsoil. So if you’re constantly watering the top of the soil and the surface of the soil is wet, you’re always losing water through that evaporation. But soil itself is also very good at capillary action. And by that you know it’s like when you if you use a piece of dry kitchen towel to mop up the spill on the work surface and you put the kitchen towel on the edge of a bit of water then the water is drawn sideways or longed. The along the kitchen towel. And that’s, that’s capillary action. So you can pull water sideways, and even upwards by capillary action. And that happens really well and a good quality, you know, healthy soil. And so that’s how these systems work, they draw water back into the root zone by capillary action, and that wick can then deliver water as the plants need them. If the plants are not drawing water, away from the soil, the root zone will remain moist, and that capillary action just won’t work. It’s not you know, it’s not like a really strong pump, it just is a very gentle, slow way of delivering water where it’s needed. But keeping that water away from the surface so that it doesn’t evaporate.


Sarah Wilson 15:46

Thinking about the styles of gardening, obviously, we’ve mentioned to permaculture, is there a style of gardening that particularly lends itself to waterwise gardening?


Janet Manning 16:06

Well, I don’t think there is I think, I think whatever you do, you can probably do it more sustainably than you currently are doing. I mean, even I, you know, there’s things I can do that, that would be better. And when I mean sustainably, I mean, not just thinking about water, but thinking about all of the things that you do in your garden. You know, if you think about water management, in general, then one of the very best places that we store water in the UK is in peatlands. And yet we go and pick them up, to put that PEAT in containers to grow things in our garden, and then use mains water to go and water. And that’s not sustainable. And we need to change some of the things that we do in that respect, to be able to make things sustainable with we’ve all got to do that for everybody’s sake. So I think whatever you do, you know, if you’re just trying to think of anything that is particularly water wise, I don’t see that there’s any reason that any of us need to stop growing whatever we want to grow, as long as we do it in the most sustainable way that we possibly can.


Sarah Wilson 17:26

And thinking about gardens in the wider environment gardens due to make up quite a large land surface area in the UK. And obviously, they’re an important part of a wider network. Everything that you do in your garden is going to have implications for the wider network, that are there specific things you can do in your garden that do, you know, do help the area immediately around your garden? And in fact, the the larger area around you?


Janet Manning 17:51

Yes, absolutely. I mean, if you talk about sustainable gardens, and I think the one thing that we should not be doing is watering our lawns with mains water. So if you think about sprinkling a lawn with mains water, it can use as much water in an hour as you would normally use in your household for a whole week. So that’s a whole week’s worth of water supply gone on your lawn, for what purpose, just so that it can look green, there’s way there’s ways that you can maintain a green lawn without having to use mains water to water it. And it’s all about keeping the soil healthy underneath it. It’s about getting that right mix of water and air as I was describing earlier about keeping the oxygen in the root zone and hollow tine aerating and doing it in the autumn, so that that encourages the autumn rains to get down into that root zone. And that helps the roots grow deeper. And once the roots grow deeper than they can get access to more water from deeper layers. And that helps the grass then stay greener for longer during the dry spell. And if you’ve chosen the right variety of grass, then you can you can get deeper rooted grass varieties that will help to keep that that that lawn cleaner. So you know, if you do want a pristine green lawn, there’s ways of doing it without needing to use mains water. And I think that’s what we’ve got to do is look for those ways that don’t impact on everybody else. Let’s not forget that. If we’re using mains water, we’re taking that water from rivers are groundwater that that would otherwise supply rivers. And then there’s a whole host of wildlife and aquatic environments that we are then helping to, you know, not maintain as healthy as it could be if we’d left that water in the rivers. So that’s what we’ve got to be doing is looking for a sustainable way of doing things.


Sarah Wilson 19:52

Yeah, that was one of the questions I had listening in to you then. So obviously as you say we live in a fairly wet country. What is the problem with us using water? Is it just that we’re if we’re taking it during dry spells, we’re taking it from places that would otherwise need it?


Janet Manning 20:06

Yeah, absolutely. So if you if you’ve been listening to the, to the news recently, there’s an awful lot of public discussion going on about the environment, the oil and water industry and all the rest of it. But on the whole, the water industry is really short of water. So it’s not that long ago that there was a complete review of water resources right across England. And the conclusion then was that we are short of water by about three and a half million litres of water per day. In England, if we continue to use water the way we do at the moment, by 2050. And obviously, because of climate change, we’re going to get those dry spells, we do all tend to use more water during dry spells. If you have a really bad flood, then lots of water tends to get used in actually cleaning up those floods. If you have a wildfire, you end up using lots of water to put that fire out. So there’s lots of sort of compounding aspects to this added to the fact that, you know, the UK does grow still quite a lot of its food, you know, think about East Anglia and Lincolnshire there’s an awful lot of potatoes grown over there. And they’re irrigated to be able to do that. And it’s probably still better for the UK to irrigate potatoes and grow them in the UK than it is to try and import them from somewhere else where they’ve got even less water resources. And then you’ve got to transport them into the UK. So we’ve got choices, we’ve got to make those choices, do we want to grow our own food? Do we want to use water to generate hydrogen, which is obviously going to be a much greener fuel as well as we’re using green energy to produce it? We’ve got lots of priorities coming up against us. And so I think everybody would probably agree that actually keeping a pristine green lawn green with mains water compared to growing food, generating power, keeping the soil healthy, by allowing the water to wash your hands, you know, we just got to make those priorities and we’ve got to change attitudes to be able to do it.


Sarah Wilson 22:25

I mean, I like to think that most people aren’t sitting there just going, Oh, well stuff the water stuff, the environment, and I think most people are concerned. The bottom line though, is, if you’ve got a lawn, a lot of people have got lawns, you know, I’ve got an area of it in my garden. I’ve reduced it, by about 75%, but still have a small piece. If you want to irrigate your lawn in the summer, you know, and that’s the way forward you want to go you want a green lawn, it to me, it seems much easier to plug in a sprinkler, let the sprinkler kind of do its thing, move it a few times around the lawn, and then that job done. If I want to irrigate it with rainwater, I think probably it’s a much more difficult and time consuming process. And I think that is maybe an issue for a lot of people, you know, they may they may have had their fingers burnt with previous technologies that promised that you could your grey water, and then they didn’t turn out to work. And I think there’s just this thing that actually uses recycling water conserving water, you know, and using the rainwater that you harvest is actually quite a difficult thing to do. Is that true?


Janet Manning 23:34

Yeah, water is so convenient, switch on the tap, it turns up every day, you don’t have to order it in. You know, you don’t even have to pay for it straight away. It’s really convenient. And it’s really easy. But let’s not forget it was originally intended that way because of public health. You know, it’s clean water is what keeps us all healthy. Not for watering lawns. I totally agree with you that it’s so much easier to just put the hose on but how many people actually measure how much water goes onto their lawn. And even the simplest thing like next time you put a sprinkler on, stick a few empty jam jars under your sprinkler and just see where that water goes and how much ends up in your jam jar. When you’ve got an inch of water in your jam jar, you’ve got enough water on your lawn and you can switch it off. You know, it’s it’s simple things like that. That would make a difference. If you leave the sprinkler going on overnight, because it’s convenient, you want to give it a good soaking, you’ve probably wasted you know you leave it on for 12 hours you’ve probably wasted 11 hours and 14 minutes worth of water because it really doesn’t need that much. And that’s what I think is the difference is that the excessive use of mains water because it’s so convenient and easy to do that we’ve got to get over. And like you say, it’s about knowledge. It’s about, you know, getting people to understand how much water is really needed. Stick an inch of water on your lawn, not any more, it’s just going to drain away and be wasted anyway.


Sarah Wilson 25:14

Yeah, okay. Well, that’s good advice. And like you mentioned, obviously, we’re heading to a time of extremes of weather and we don’t actually know really what we’re in for. Can you elaborate on that? Are there any indications based on previous data, you know, how things like rainfall patterns or the amount of rainfall is going to affect us in the future?


Janet Manning 25:37

It’s a difficult one, isn’t it? When I look at some of the floods that we’ve had this summer, across Europe it’s quite scary, news, items that have popped up from from the flooding point of view, and you think that’s in the first lockdown, you know, we had a very dry spring, it was lovely and warm, everybody was out in the garden, everybody was using the water. And we used horrendous amounts of mains water during that first lockdown. And there were places where the water use went up by 70%. And unfortunately, because the system was not designed to do that, that meant that there were some people that actually couldn’t get water to their houses, because there was so much water being taken out of the system of distribution system that people who were on the end of the line, the water just wasn’t getting to them. So yeah, it’s difficult to predict. There are lots of water management plans in place within the water industry. So if you’re interested in the detail of that, you know, if you just look at water resources, for example, there’s the national framework for water resources, which was published a few years ago. That’s lots of detail on how they manage the longer term aspects of water resources.


Sarah Wilson 26:54

Are there any other resources that you’d like to share with people?


Janet Manning 26:58

I think the Mains to Rains website is really helpful for gardeners. So what we’ve done there, we’ve tried to incorporate all the really simple retrofit, you know, we don’t want people to dig up the whole garden and change the whole thing, but actually retrofitting simple things, then can really help so things like water butts the obvious choice, keeping your soils healthy, by adding compost, and mulch. Mulch is really, really helpful because it stops the surface evaporation again, just choosing what plants for the right places. So you know, if you’ve got a shady, damp or spot ferns, the sort of plants that enjoy those shady areas are going to be much happier. And if you’ve got sunny areas, then ferns are going to be really upset and unhappy in the sunny places. So getting the right plant in the right place will mean that you need to use less water. Lawns the big one, which we’ve talked about, and even simple things like just placing a saucer under a container, they can make a difference. There’s 30 million gardeners in the UK, if everybody’s got one saucer under one flower pot and that flower pot is normally watered through the summer. You could save enough water to supply 2 million people for a whole day through that summer. So that’s you know, it’s small actions that add up because there are so many gardeners in the UK and that’s what makes a difference. So yeah, do you have a look at Mains to Rains, we are asking people to pledge to make those switches in the garden to help us conserve more rainwater. And as of this morning because I’ve just looked this morning again, we’ve managed to already identify 10 point 5 million litres of water per year that could be switched to rainwater. And that’s for a relatively small number of gardeners. So the more people that do it, the more we can show the potential that’s out there for making use of that rainwater.

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