Cassian Schmidt's full interview for Verde es Vida

1. You have travelled a lot over the years, including a recent trip to the Pyrenees. What were you after in el Valle de Ordesa y Monte Perdido, and what other areas would you like to visit in Spain?

I am pretty familiar with Spain, and I am always interested in these higher mountainous areas of Spain. Usually, it is just for holidays, but as a Landscape Architect, I always try to read the landscape and read what could be behind, such as the cultural influence of grazing. But the Pyrenees are beautiful for hiking, and the weather is better than in the Alps. We started years ago in the Eastern area, around Canigó, and now we are going west. Last three years we were more in the centre, on the Spanish side. It reminds me of the steppes in Kyrgyzstan, on the highlands. And the vegetation is not far away from what we have in Germany.

I have also been on the Sierra de Grazalema, which has interesting spiny cushion formations and an attractive plant community where this Abies pinsapo grows. And I have also been to Picos de Europa, where many of the perennials we use come from. Like the Eryngiums or Digitalis parviflora, this last been an excellent plant for landscape design, and it is not used enough. And of course, I have also visited some of the most famous gardens in Spain, like the ones you find in Andalusia, Sevilla-Granada-Cordoba, or the foothills of Sierra Nevada, Alpujarra. However, I have never been to the higher elevations.

But I aim to return to the higher elevations of the central areas of the country. Including the surroundings of Madrid, as I believe they are pretty interesting.

I have collected some seeds from things like Retamas on this trip, proving hardy in Germany. I find Spain is a good source of plants and ideas, from the perennials on the higher lands. With such a rich flora, only very few are used in nurseries, and most likely not in Spain. The inland parts of Spain would benefit from using these higher elevation perennials.

2. Are there still many areas that you would like to learn and incorporate into your research habitats? For example, where does your interest lie now and in future trips?

Now with Covid, I am very centred in Europe, and Europe is highly diverse. There are so many areas that I have not been to. For example, in the mountains in Italy and Sicily, James Hitchmough was in Sicily in May and a friend in the Sibillini Mountains. Both areas have mind-blowing dry meadows with beautiful structures and great models for planting designs. However, these regions are not completely dry over there, so plants might work well in Germany. I want to visit these Italian mountains, which makes me realise I don't have to go too far to explore new areas.

Central Asia is a fascinating area for me, and I hope to come back soon, Kyrgyzstan to be more specific, and it is almost unexplored. There are so many exciting plant communities over there. You can learn a lot from the semi-steppes and the steppes as they are beautiful and are very connected to the drier areas in central Europe. Many of the plants over here migrated after the Ice Age about 5-6 thousand years ago from Central Asia. Now they are nature reserves, and they are managed by men, very similar ecotypes.

I have also visited Chile and South Africa, but I found out that those plants don't grow well in central Europe, but I think they will probably do well in Spain.

3. What is the advantage of the habitats and planting groups you have researched regarding climate change and why we should incorporate them?

We are already facing climate change effects, especially in our cities with the heat island effects. It is like having the climate of two latitudes further south. So in cities in Germany, we have climates more like northern Italy or Hungary and other areas further east. So then, it makes sense to concentrate on plant communities from these areas or ecotypes from these areas. And we try to incorporate these plants and ecotypes back in Germany.

We look for plants with a wider ecological range, not necessarily new species, but species that we already might be using and that we realise will support the effects of climate change better. Especially regarding trees, although this is not my expertise. For instance, Acer monspessulanum or Acer opalus are still not very commonly used yet but are highly suitable for the future. So you don't need to go very far to find new sources. Same with Oaks, like Quercus pyrenaica, Q. faginea, which will be better options for Quercus used in the landscape in the future. For me, these adaptions are especially important in city areas, not so much on natural landscapes. Many natives are not coping well already in our cities, but introducing non-natives in natural landscapes could be an issue. There is a lot of debate at the moment with this native and non-native topic. The more we rely on natives in our cities, the more we will rely on fewer species as time passes, and cities' biodiversity is also essential. I find that most landscape architects nowadays are not knowledgeable enough about plants, and they tend to use a very reduced palette that tends to be always the same, and this is not the way to fight climate change.

4. Of those examples and situations that you have tried to mimic in Hermannshof, what has been the approach to maximising plant exuberance?

There is always a scientific base, the right plant for the right conditions and place, observation and evaluation of the site. You want plants to be ecologically friendly to the area that they are going to be planted. The second most crucial issue is to get the right proportion of plants, which goes hand in hand with plant sociability; not every plant works well in larger groups or as individual plants, so this knowledge is fundamental. Also, what we aim to create is a community of plants, but a dynamic one, not like an old fashion border. This means it is not easy for the maintenance teams, maintenance teams need to understand the importance of these plant communities not being static, and they will look different every year.

Gardeners need to observe what is happening, know the history of that planting, and have a guideline for the future. The more naturalistic, the more intellectual planting becomes. And the maintenance team needs to have this intellect, be capable to decide what to do. Like understanding which plants are gap fillers and you need to keep seeds and seedlings for filling the gaps, or which plants are taking over and you need to control. Maintenance teams should know about the plants and the dynamics, and then you can get this exuberance.

We have predesigned plant mixes, like modules, which are trials for five years and during this time, we get to understand the plants in the combination and how they perform. The best plant community is nothing if it is not maintained correctly and can quickly go to rubbish in a couple of years, especially from an aesthetical point of view. It is a misunderstanding that naturalistic planting can renew itself without any input or guidelines from human beings.

5. What is required to make that planting thrive? And once established, what is the maintenance like?

Soil preparation is vital; the soil needs to be weed-free. So, we introduce a layer of 10-15cm of engineered or manufactured soil mixes in professional public green, which should always be weed-free. They are mostly 100% mineral, and then we mix them with 10-15% organic matter. But, still, it is critical to keep it very low. So, to get weed free starting conditions, this is very important both for planting and sowing.

And then you need an excellent balanced plant community that has the potential to perform during 10-15 years, which is quite a lot for perennial planting, and of course, it depends on the management. So we used the ecological plant strategies from John Philip Grime and adapted them to maintenance models, so we have three directions:

One is for stress-tolerant planting types (like most Mediterranean plantings that thrive in full sun) and plants that grow under trees in the shade, as it is another type of stress environment (lack of nutrients, light and water) too much of everything, like wetlands. We enhance and keep the stress; otherwise, the planting tends to shift to other more competitive types of planting; if you don't follow this, then the maintenance for this kind of planting goes up. This kind of planting is the one that produces higher biodiversity, even if it sounds counterintuitive. In ecology, stress means more niches and hence higher diversity. Although we take all the organic matter away (in Germany), it is probably not the best approach in a Mediterranean climate.

The second one is for competitive planting types: typical central European forb communities, taller meadows, prairie plantings, high grasslands (tall steppes), woodland edges, tall forb communities, which have higher biomass. They have all the nutrients and needs they need, and they are very competitive, so by the end, you tend to lose diversity, which is normal. Here you have fewer plants, and they grow in bigger groups. And it is key for Landscape designers to design them in larger groups. Here we use recycling systems, we leave all organic matter on the site, and we shred it down and use it as a self-composting method. We don't put anything in or out. With this method, we have observed that plants get richer over time somehow.

The third is the ruderal model, with pioneer plant communities colonising gaps; these tend to be new plantings that do not last for long. But it can also be used in Landscape planting design for annual seedings and annual meadows. These are ephemerals, temporary plants. And we mulch at the end of the season before we start again, so there is no disturbance in the soil (mineral under stress areas, organic on competitive regions).

Using these models, you can predict the evolution of these plant communities and manage them. So it is less about plant communities than maintenance. Then you can start asking questions like what happens if I introduce disturbance like mowing, which usually enhances diversity, especially in the competitive plant communities. Or, in Germany, taking away organic matter to improve stress (the environment it's often not stressful enough).

This plant community model for maintenance is now mainly accepted by the universities, even though Grime never intended it for maintenance. But it is a suitable method that I believe works in every climate as these three plant strategies are the same worldwide. Of course, there are some mixed strategies, but we have simplified them into these 3 to understand them. This method has been sustained over 20 years of research in Hermannshof, with every plant species recorded in a database. But also how much maintenance they require and of what kind it needs. And this can be used for projects, Piet Oudoulf uses these calculations to maintain his planting of the Highline and Millennium park, and these calculations change based on the type of climate.

The classic English border with constant replanting, hence disturbance, is the one that requires the highest maintenance of all. If we take plants in dry shade, maintenance is below 1 minute per sqm for sunny, dry areas, and stepper planting is between 3.5 and 5.5 minutes per sqm per year. In comparison, the classic border takes about 12 to 20 minutes per sqm. And if you spend higher, you are doing something wrong.

In the public sphere, we want more quality, more diversity, more dynamism with less input. But it all depends on the training of the maintenance team. And most designers do not understand this; we need more connections between landscape architects, the maintenance team, and maintenance to know more about landscape architecture and design. It is not just about weeding but enhancing the visual effects and exuberance. And it is the most challenging part. Also, gardeners like to have a routine, but this is the wrong reasoning because plantings develop and change; you always have to make decisions not to follow guidelines.

6. Your ecological approach combined with this kind of maintenance is ideal for the future of gardening. But your understanding of ecological gardening also involves non-natives. Could you explain your ideas and what is this ecological approach about, and how can native and non-native be incorporated?

There are two levels here; one is for aesthetical reasons, in cities it has to look good. And if you just let nature do in city environments what you get is just rubbish. Only in large open landscapes outside the city, this can work. In the city, you cannot escape human design and influence, an adapted or enhance nature. Also, the plantings are more garden environments, even if you manage some spontaneous planting. On some famous examples, like the famous Duisburg Nord by Latz and partners, they didn't understand that they needed the planting to be managed. Over the years, all the design areas meant to represent different ecotypes tended to look the same and not good either; they all end into woodland in Germany. Everything is overgrown, and there is no visual diversity or light anymore. It always needs management in a city. In Berlin, they have management plans and introduce disturbance every five to 10 years, so they get back to the starting point. And also, in gardening, you need this understanding. So on this ecological approach, it is a combination of ecological goals: diversity and dynamics, but it also has to be aesthetical for me, at least a science of design, the science of human care.

Here in Germany during the 70's and 80's we had this idea that nature knew best, so we stopped maintenance, and we left everything to go on its own. And what happened is that everything tended to be overgrown and not aesthetical. And nowadays, we have shifted again to human management and the importance of this visual ecology where you still enhance diversity and dynamics. But most of the public still has this wrong idea of natural gardening that means you don't need to do anything, but it is wrong.

And there is a strong link between the Native and non-Native discussion. There is a natural obsession with the gone native. But most people do not understand what this means, especially from an aesthetical point of view. They often need to experience these non aesthetically plantings to realise that this is not the way. It cannot be colourful and long-time blooming, as native plants have very adapted specific periods where everything happens, and there is not much interest outside that range. So we need these mixed native and non-native plantings in our cities to have diversity and be aesthetical. This obsession with natives and aesthetical plantings in Germany sometimes pushes for alpine plants in the cities, which might be native but cannot thrive in a city environment.

Several pieces of research have been published that prove that this mix of native and non-natives creates the richest biodiversity, and there are more insects and rarer on these than on only native plantings. And, of course, the aesthetical performance as well (Great Dixter study). And if you don't mix, you would have minimal times of the year where interest happens. So I believe 60% native and 40% non-native are a good balance.

Of course, you can't introduce everything, as they could cause problems, and that is why it is good to carry research before as we do over here. Even the old Nature Garden movement now facing climate change has opened up, and they have recognised they need plants for further afield, not just the current plants native from Germany. Also, it is interesting the contrast between city plantings and what is left of wild nature around them.

7. Your work involves a lot of research and travelling, but what you do is also very focused on planting that can be used in Germany. What types of habitats you have researched do you think share patterns with the different climatic conditions of Spain?

The ideal would be Steppe communities and grasslands, south-eastern European (Balkans) and central Asia plantings. Especially the highland semi-desert plant communities like in Kyrgyzstan, also are adapted to salty soils, which are great for traffic areas in snowy places, as road salt would not disturb them. The mid-west in North America, with dry summers and cold winters and very unpredictable weather patterns, is very similar to the continental climates in Europe.

For Inland Spain, it would be good to look into Mediterranean mountains with beautiful plant communities, like the spiny- cushion communities (Fabaceae; Genistas and so on). We should look into Turkey and the eastern Mediterranean on your same latitude, which has quite different species like Acantholimon. In the United States, we could use the sagebrush communities like many artemisias that grow on high altitude deserts and plants from Texas. And, of course, the subshrubs from the Mediterranean garrigues and stepper formations. A lot of plants are cold hardy. I think it is wrong that in Spain, the main focus is to emulate central European or United Kingdom types of planting and gardens. Also, you would not depend so much on irrigation, and you could use only mineral mulch, but also that way you would enhance biodiversity. To emulate English landscapes in southern Europe is not very clever.

8. What sort of approaches do you think could be incorporated into Mediterranean climates that you feel are not so exploited now? For example, could you suggest unusual plants that you think could thrive in Spain, even in those interior areas with cold winters and hot, dry summers without summer rains?

I think the plantings from Fernando Martos and Miguel Urquijo are a thriving mixture of eastern European stepper plants and Mediterranean subshrubs and some short prairie plants from the mid-west of the United States. Or even these shrub plants and semi-desert plants in Kyrgyzstan, like Perovskia. Perovkias perform better in southern Europe with cold winters and dry summer summers than in central Europe. Same with the grasses like the ones from northwest America, or so much unused ones from Spain itself, the tussock grass communities from Alpujarra are beautiful. I use them here, but they are not used in Spain and also many Festuca species.

9. What are the Mediterranean areas that you feel have more interesting plants incorporated into nurseries? What would you like to see more often?

Euphorbias is a significant group of plants that I think you could use more often and are still underused. For example, shrubby Salvias, there are hundreds of species that could be used. A lot come from Europe; many are variations of high-altitude Mediterranean species and a lot from California. Artemisias, Fabaceae family plants, Retama species like Genista aetnensis. But my main recommendation would be to use more umbellifers. Spain has many, the best umbellifer plant communities I have ever seen, but again these are underused or hardly used at all in your country. Ligusticum lucidum from the Pyrenees is an example of a beautiful umbellifer. Teucrium lucidum is a beautiful shrubby plant that you can even use to make hedges. Seseli, for example Seseli gummiferum. Marrubium species, for instance Marrubium incanum. And these lower grasses from North America, Schizachyrium and Stipas. And if you look for them, most are in cultivation; for instance, Olivier Filippi would have most of these plants.

There is a garden in Marseille, France, Le Jardin des migrations, consisting of only garrigue plants. Right on the border of the sea, and I think this is the best model for the future gardens of the Mediterranean, and how public green parks could look like. And it is a garden without irrigation, I believe the plants come from Olivier Filippi's nursery. Also, Olivier's show garden is beautiful, and his books are worth reading to fully understand Mediterranean plant communities and their dynamics. This kind of public spaces would work on coastal areas, while interior regions need more continental cold-hardy plants, and could go with the mix of stepper plants, short prairie or mixed-grass prairie, eastern European and a little bit of high land Mediterranean -which are plants with good structure-. But I also collected some seeds from lower land Mediterranean plants in Corsica at sea level, and some are still incredibly cold-hardy plants. And the reason is that in the past, these plants evolved with colder winters than what they often experience now. So it is a matter of doing plant trials and observe if they can withstand inland winters or not.

A good source of research could come from Madrid Botanical Garden. I often check their seed lists and know what they are growing, and there are often plants that prove to be cold hardy on their trials. Unfortunately, most of these species are still not available in nurseries and not used in landscape architecture. But we use their information as a source for us too.

Another thing that I think should be used more often in countries like Spain is rain gardens, often misinterpreted for rainy climates and wet soils. And I even see many designers here in Germany designing them wrong, using the wrong plants almost 100% of the time. So plantings often fail, as they use plants that should be on waterlogged soils but put on free-draining soils instead. Rain gardens are intended to be for heavy storms that create floods, and they should be very free-draining soils. So, we are talking about drought-tolerant plants that can withstand a few hours or days of heavy rains. But 99% of the time, they would not receive any water, and the soil would be an utterly free-draining bioswale and often next to parking lots, so on arid environments. There is a need for more literature on what plants can be used, and I am currently assessing what plants can be used on bioswales and rain gardens; even shrubs and trees should form part of this system. But there are still a lot of technical issues that need to be thought of. But I am sure this should be a must in the future, and something to think about, especially in the Mediterranean areas with high rainfalls in very short times. So garrigue plants should be perfect for this task.

10. As I understand, part of your work has also involved creating ready-made mixes that the public can use. Do you already have blends that could be used in Spain, and if so, which ones do you think would have more chances to thrive and succeed over here?

You could adapt most of our mixes, as we don't have combinations with subshrubs, but most of the mixes for the dry open space could be used in the cool winter areas around Madrid and central Spain, so inland and continental regions. A lot of the plants that Fernando Martos and Miguel Urquijo use are also part of these mixes. Even the dry prairie mixes would grow well in these areas. So, we have about 18 to 20 mixes that would be useful for Spain. And coming back to things I would like to see, it would be great if people in Spain started trialling garrigue-stepper seed mixes and making them commercially available. I am unaware that anyone has done garrigue seed mixes yet, but I believe they are possible.

The best way would be for nurseries to start collaborating closely with scientific organisations and botanical gardens, which is how it works here in Germany.

11. You participate in many scientific and horticulture talks all over the world. Have you ever done any in Spain? And is there any professional from here that you would like to meet?

No, never in Spain. I have done many other areas with Mediterranean climates, Italy, France, Chile, Australia. And for me was a process of adapting my thinking to different climates and environments; at the same time, these proved to be interesting because these places have climates with more restrictions in resources, both from climate and workforce experience than what we have in Germany. So these made me reflect on my approach; for me, Australia was incredibly challenging; I had to think of how to apply our findings and strategies, but it was possible because ecology works in every climate.

Regarding someone I would like to meet, I follow Fernando Martos work, but I don't know him. And I feel Fernando Martos is the person in Spain that does the closest to the kind of work that I do, and I think he has a fascinating approach.

I know many scientists who do plant research in the UK and France, but I can't think of any from Spain, most likely because of the language barrier. But in general, it is more important for me the applied science, and that comes from designers who are willing to go the extra step. How they deal with their climates, how they combine plants and plant communities. For example, Germany looks into designers of Mediterranean climates, Australians take influence from Europe, and combine this knowledge with their plantings and local conditions. So it is not about mimicking but about adapting, which I find is the most exciting approach. How people face limitations should be necessary for everyone to understand, as we face climate change. Our climates are inevitable changing, so our climate in Germany might end up being like the one you have in Madrid now. And looking into what you grow over there might prove critical to understanding what we should grow in the future.

12. How do you see gardening professionals and plant specialists in the future? How do you think these professions would evolve?

The main problem is the maintenance. Professionals should understand that without maintenance, all their designs are nothing; they have to connect and think about the maintenance. Not to design and think it would be taken care of. In Germany, we already have this way of design thinking on habitats and plant communities, involving the dynamics, design in the long term and the evolving plant communities. So it does not make sense anymore to think of designs as static pictures. This also relates to climate change, which will force change in or plantings, so we need to think of resilient communities that will adapt to changing conditions.

The second key point is the connection between plant specialists, usually not designers, and the designers. Designers should go to specialist nurseries and speak with these people to get the knowledge and know-how. All the specially selected plants are nothing if they don't get used, which is also very frustrating for the nursery trade and plant specialists. Another way for nurseries and plant specialists to showcase what can be achieved should be to have permanent show gardens where designers can go and experience the plants themselves and understand their requirements. Sadly, all these professionals are perceived as different groups nowadays, and they don't interact as they should. They don't understand each other. For me, the tension between landscape architects and garden designers is the perfect example; they tend to criticise one another when they should be collaborating; there is a lot of criticism on garden designers coming from Landscape Architects. But garden designers' plant designs tend to be much better because they get more involved in the design process with other disciplines.

Meanwhile, Landscape Architects don't tend to get such close interactions. Also, depending on the countries, the profession changes; for instance, in the United States, most landscape architects don't even mention plants. There is a total disconnection between planting designers and landscape architects over there. While in Germany, this is a fundamental part of the profession.