You are currently seeing a placeholder content of YouTube. To access the actual content, click on the button below. Please note that data will be passed on to third-party providers.
More information
Anke Plehn
How much does your balcony support? Tips for balcony greening from an architect’s and building biologist’s perspective
Dipl.-Ing. architect Anke Plehn was born on the outskirts of Dresden. After studying architecture, two encounters gave her life a new quality and broadened her thinking: her encounter with the Austrian agronomist and permaculture practitioner Sepp Holzer from the Krameterhof permaculture farm and with building biology at the Institute for Building Biology + Sustainability (IBN). In addition to her experience as a structural and urban planner, office and project manager, building biologist and mediator, communication trainer and coach, the focus of her current work is project development, holistic consulting on building biology and ecological construction in the countryside, especially on the renovation of old farms and houses, lecturer, book author and Online congress organizer„Healthy living — building — being“ 2022 and „Self-effective healing of people and nature — mastering the transition“ 2023. More about Anke here.
Content of the presentation:
How much does your balcony support? Tips on balcony greening from Anke’s experience and perspective as an architect and building biologist.
Anke provides us with her presentation — Thank you Anke
Books
The books can be ordered directly from Anke (architektin@ankeplehn.de), with free dedication if desired.
Social Media
Website
Your two online congresses
- „Healthy living — building — being“ 2022
- „Self-effective healing of people and nature — mastering the transition“ 2023
If you would like to order your congress package (both congresses) or individually (https://ankeplehn.de/online-kongress/) orders and buys directly from Anke at architektin@ankeplehn.de gets 10% discount.
English 
Deutsch 
31 Responses
Dear Anke Plehn, dear Birgit Schattling
Thank you very much for the super exciting structural analysis lecture, Ms. Lehn.
We live in Hamburg in a new building from 2011 and have a north-facing balcony and a south-facing terrace, which is also above our neighbor’s apartment.
So both are not free-standing.
We have 3 birch trees (which used to grow wild on the roof) and a cherry in a lilac. We think that’s totally ok statically, but maybe we should consult a structural engineer.
But I have one question in particular about the water drain.
The area has gravel on the edge and paving slabs on the rest. There is always „wild growth“ in the cracks, but we left it at the edge because it is too beautiful, with evening primroses, goldenrod, bluebells, magerites and especially chives underneath.
Do you think they can stay or will it create a drainage problem at some point?
Best regards, Bine Beeken
The water drains well.
Dear Bine Beeken,
Thank you for your feedback on the congress and my presentation. Your questions are difficult to answer from a distance. It remains unclear to me which layer structure is present in each case and how and from which material the water-bearing and water-draining layer was installed under the covering and gravel strips. In the case of walk-on roofs/balconies/terraces, it cannot necessarily be assumed that a root-resistant membrane has been installed (even this cannot be overused forever). Depending on the plant, the roots seek out moisture and darkness to a greater or lesser extent, so they go through the smallest cracks, faulty overlaps … and their root growth can cause damage for a long time without being noticed, even if the water is currently draining away. To prevent trouble later on, I recommend keeping the drains and drainage areas (gravel bed) clear and transferring emerging seeds or small plants into pots and placing them on the balcony or patio (also above the gravel bed) so that no roots can penetrate. Roots are quite explosive due to their thick growth. The obligation to keep these sensitive building drainage areas clear and clean is often included in the rental contract or — if you are buying — in the building specifications.
I am planning a BLOG article with a presentation on greening facades and balconies on my website wwww.ankeplehn.de . If you are interested, please sign up for the newsletter (https://ankeplehn.de/newsletter-anmeldung/)
Good luck with your greening!
Dear Ms. Plehn,
Thank you very much for your rough remote assessment.
With a heavy heart, I will probably use the next few weeks to train the beautiful wild growth and put it in containers!
Maybe chives don’t root so badly and can stay?
Just yesterday I had a visit from my friend, who is also an architect, who also advised me to minimize „crack growth.
Safe drainage is of course important in the long term.
Kind regards, Bine
Hello bee,
I would definitely remove the goldenrod, because we don’t want to encourage invasive plants.
Source Narura DB
fantastic lecture, thank you very much for the quick introduction to static problems. It helped me a lot. Now I just need the giant scale for my buckets 😉
Thank you, thank you for this extremely informative and entertaining lecture!
I enjoyed it from the first to the last minute and learned a lot and — I am much more reassured about the load-bearing capacity of my balcony.
And new ideas are already bubbling up…
Many thanks also to Birgit for this fantastic congress!!!
Best wishes to all participants
Barbara
Hello Anke,
At the beginning of the week, another speaker had very impressively recommended perlite as a way to save weight when increasing the load on balconies.
I still have my doubts as to whether the recommended (hydrophobic) Bau-Perlite should be the material of choice for this, but in principle the idea of replacing a larger part of the substrate with Perlite (with a dry weight of approx. 100 grams/liter truly light as a feather), IF load limits of balconies could be at risk, is not a bad idea. What do you think of the idea?
A little niggle in passing, as the greatest danger for overloading balconies can probably come from sandboxes, because nothing is heavier than sand (average dry weight: 1500 — 1650 grams / liter): Mathematically, this may be true, if sand can contain 40% air voids and these are saturated with water, that it would mathematically become a good 21 % heavier by this displaced air, i.e. it would then weigh around 2 kg / 1 liter when saturated with water. PRACTICALLY, however, sand is known for hardly being able to absorb any water and, in my experience, sand cannot absorb 21 % of water (in the case of sand where I measured this once, it stopped at 13%, and that was already far more than it should „actually“ absorb according to the textbook… *gg*).
I would not recommend perlite. It is made from a volcanic rock glass and is therefore of natural origin. But the manufacturing process is very energy-intensive, the transportation, packaging … which substances are already geogenically integrated or added — there is no full declaration obligation in Germany. Ecologically, I see such „facilitations“ as part of the problem we currently have on earth. Why don’t we want to green balconies sensibly and in moderation, rather than just exhausting this wonderful idea?
And with regard to the plant, I would like to point out that although perlite can store water (and heat) over a certain period of time, it cannot provide the soil life that plants need to thrive. Logically, a different microbiome forms and the fine roots need contact with the microbes to absorb water and nutrients and release sugar. As a building biologist, I have been called into homes that smelled of mold, where children were getting sick … Cause: hydroponics, too much humidity, mold in the water … Microbes ensure a healthy, balanced (pH value) soil. Who regularly checks the water level and condition of the substrate? Sure, this can be monitored by AI — but who monitors it and where do battery and device raw materials come from? Is that ecological?
Let’s take pleasure in what the balcony can carry without suffering damage rather than trimming or testing it for performance.
Volker, sand does not retain water if the water can run off unhindered from the sand layer. In a closed container or a dense sandbox, it can absorb water — in percentage terms depending on the grain size — until it is saturated.
This is how drains and aquifers function in the soil, which collect water as a natural water-bearing layer with a high clay content in the soil under sandy or water-permeable soils.
So deduction for perlite in the eco grade…
Because of the optical quasi-similarity with polystyrene, this feather-light miracle material will probably not spread very far and as a soil digger I don’t like (pure) hydroponics at all anyway… — regardless of whether with perlite or expanded clay.
However, the potentially more indigenous expanded clay option (Eifel) also has the characteristic of using massive amounts of energy. It’s not great, of course, but it may be justifiable for the good green cause if the alternative is not being able to green the balcony… 😉
Contradiction to the non-retention thesis of water in sand: That’s exactly what I meant with the (max.) 13 %, that it already absorbs it — and (of course) dries out completely again quite quickly (at room temperature in 5 days). But not 20 % or more… 😉
And why no natural materials? I’m always amazed that people don’t look there first🤔
It was more logical for me. Compost, mulch, leaves, hay, grass cuttings, green cuttings, branches etc. work really well. Of course you have to try things out and be a bit adventurous.
But I’m also a bit crazy.
Dear Ms. Plehn,
Thank you very much for this great presentation. I live in an area where pumice is mined. Pumice itself is super light, I think it floats on the surface of the water and is natural. Could I use this raw material instead of sand, for example? That would have the advantage of being lighter.
Kind regards Martina
Hello Martina,
exciting question!
Whereby the figures to be found on the weight of pumice do not necessarily support the thesis of being lighter (the „range of opinion“ extends from 800 kg to 1.6 tons / m³!?).
But what it would do in any case: The air AND water (storage) capacity would be considerably increased compared to sand!
Another candidate with presumably very similar properties: lava.
In contrast to expanded clay & perlite, it has already undergone its extrusion process in a volcanic oven and does not need to be heated again to 1200°C in a rotary kiln with gas heating… 😉
Hello Volker,
I think 750 to 1000 kg/m3 is realistic. Pumice is actually the same as lava, only beige to brown. It is often used for green roofs and as an additive for cactus and lemon soil. Pumice also loosens up heavy soils.
Hello Volker,
As Martina has already written, lava and pumice are both volcanic igneous rocks. Natural pumice becomes porous when viscous lava is foamed by water vapor and carbon dioxide as it cools.
Lava also undergoes a treatment process (perhaps less than pumice?) before we can buy it as lava sand, chippings, granulate or gravel, filter material or for drainage, which I am not familiar with from an energy and ecological point of view.
Simply inform yourself, check for yourself what is consistent with your own truth and try it out
The joy of experimenting and balcony greening! Kind regards
Anke
Dear Martina,
I can certainly imagine pumice only for slimming, i.e. the function of a humus-rich living soil balanced with the advantage of water storage capacity and low weight. Please make sure that it is natural pumice, not metallurgical pumice or pumice made from coal processing residues. These contain (harmful) substances that do not belong in soil.
Simply test.
Good luck and enjoy it“
Kind regards
Anke
Thanks for the warning.
But: @“Simply test“. Hopefully this is not meant to mean that you can buy the „right“ and the „wrong“ pumice interchangeably, so to speak, if you simply ask for pumice in a building materials store…!
(The subsequent test for harmful substances would probably cost x times the purchase price… *gg*)
I remember the (natural) pumice that I once „played“ with as being rather lighter; nevertheless, the information — from building material dealers who have nothing to lose at this point — that the stuff CAN be practically (almost) as heavy as sand, is not only made easier by freedom of opinion… 😉
In other words: there seems to be pumice in very different weight classes!
Irrespective of this, the idea of being able to produce an optimized self-made tub soil with such additives popped up in the „natural extrusion oven“ (vulgo: volcano) is a very realistic option, perhaps even for the Berlin community (where there is certainly a „hotspot“ of balcony gardening) perhaps a possibility for organizing a practical event to bring people together via a bulk order (1m³ big bag)…
Dear Anke,
Thank you very much for your reply. I live near the pumice quarry and can buy the original pumice there. But thank you for your tip. I didn’t know that there is also contaminated pumice.
Kind regards
Martina
Hello Volker -
Thanks for the tip — of course not “Just test the „right“ and the „wrong” potting soil and, for example, in a sunny and shady location, with regard to watering over a certain period of time,…
And in terms of weight — nature is diverse!
Good idea with the bulk order (1m³ big bag) — just store it temporarily so that it can bear the load … 😉
Anke wishes you much joy and enriching cooperation
The presentation was again very informative. Thank you very much! Then maybe I can think about adding a balcony solar system to the front. They are now also available in a lightweight version. Together with the plants, that would be the ultimate in climate protection in the smallest of spaces. This month, a new guideline for listed buildings was introduced in Lower Saxony, so it may be possible to install a solar system there too.
Thank you for your feedback and good luck with your projects! Sincerely, Anke Plehn
Dear Ms. Plehn,
About the video Organic balcony: Bees and lots of fruit: I had to laugh as you talked about all the fruit that was produced and that people didn’t want. They should be happy that they don’t have to buy the expensive products from the supermarket. Well, our laws also contribute to the fact that many people just don’t want to get into trouble. You keep hearing about the difficulties of others and what a Ponzi scheme it is. No wonder people are withdrawing.
Keywords: I particularly liked what you said about remaining individual and on a human scale.
Or: As you and Birgit Schattling say: just start. That’s what I did and was able to make some wonderful observations — I’ll save the details for now — this comment will be too long.
About your website: After the organic balcony video, I looked at your website — Perma Architecture — and there, too, I read about your tremendous work on yourself. Your unbelievable positivity as I could already hear in the video. Unfortunately, I am only partially successful because I have great difficulties here in my living space caused by mobile phone technology. I could do with some building biology advice. I would probably like to give you a call.
Oh yes, you have videos of Iris Zimmer on your website — I have also been able to attend these congresses.
Thank you: Thank you very much for this, your presentation/lecture. Thank you for taking part — very important! It’s also great that you made your presentation available to us so I can look at it again, read it and let it go through my head. Absolutely valuable!
Best wishes from Bremen, on the Weser.
Dear Mrs. Lazar,
Thank you very much for your detailed feedback. It helps me to carry on a little, even if it is an enormous amount of work — but one that is so meaningful for me!
Regarding your living space and the (perceived? or assumed? or measured?) smog exposure in it: There are ways to protect yourself, including consciously minimizing it, shielding or harmonizing measures … but this is hardly possible for plants and animals in our environment.
You are welcome to call me, but there are very good building biologists and building biology measurement technicians in the north who can advise you on site. About the IBN https://baubiologie.de/ you can find local advice centers. Or you can listen to the interviews on Esmog in November (14–17.11.) at my congress repetition „Healthy living — healthy building — healthy BEING“ — free of charge and online. Register for NL and you won’t miss the registration information. https://ankeplehn.de/newsletter-anmeldung/
Kind regards Anke
Dear Ms. Plehn,
The presentation was really very good. We had the same topic on our roof terrace last year. Our house is a bit older. The previous owner didn’t leave any documents behind.
We had a great architect who was also involved in the houses in the area and really helped us a lot.
Statics is a difficult subject and the distinction between the terms is not always easy to understand, even for the layman. My head was really spinning at times.
Thank goodness the drains were not an issue for us. The drains are incredibly important and also that they are not blocked. I thought it was really great that they explained this. Many people don’t know that.
You explained everything so well and clearly. The examples and graphics were also really great.
Such a complex topic explained so well is simply great.
A little tip for calculating the weight of large pots and beds: Take a pot that fits on the scales and contains the same or similar soil and has absorbed as much water as possible. And then extrapolate. There are also tables for certain soils and how much water they can absorb. With tips and formulas on how to calculate. There are even calculators. You have to search a bit. But it simplifies the whole thing.
LG and thank you for the great presentation.
Thank you!!! brilliant idea.
With pleasure. I’ve done the math every year. It gives you practice. And look around for solutions. I’m glad that we’ve taken care of that. We’re now so statically secure that I can’t exceed anything I can think of 😉 And it was definitely helpful for you. It’s always important that people learn to assess this point. Many people resort to lighter materials, such as perlite, for fear of adding too much weight. I think similarly to Ms. Plehn on this point. Many people don’t dare to use woody plants for this reason. Which is a real shame. Ms. Plehn makes a wonderful contribution and perhaps also provides security. LG
Thank you, thank you, Ms. Beck, also for the reference to the calculation tables.
Yes, there are calculations, both complicated and simple. For me it was always easier to measure a square meter on the balcony and weigh the flower pot, certainly not every scale is suitable for this, the old GDR personal scales are (preferably without a handle in the middle — still available on ebay)
Sincerely, Anke
Dear Ms. Plehn,
Thank you very much for the enlightening and technically profound report, and also very much for the presentation.
We wish you continued success and pleasure in your work.
Best regards,
Pia
@Birgit: A huge thank you for this speaker
Thank you so much for sooo much in-depth knowledge and so much wisdom. I am downright touched 🥰
Susanne from Hofheim am Taunus
Many thanks to all congress participants and to those who took part in the exchange of ideas here.
Anke wishes you lots of fun with your balcony gardening
Dear Anke,
A big thank you from me too for this detailed and competent presentation. I think I watched it at least five times to make sure I understood everything :).
I had already looked into the subject a bit beforehand, as I’m one of the more anxious people, but I gained a lot of additional knowledge. In the end, I decided against growing (a) larger plant(s) on my 4 m² balcony.
I don’t know about others, but in my emotional exuberance I sometimes tend to be a plant messie. I want to cover everything I can, as many plant species as possible, for as many insects as possible and also some snack fruit … Sometimes it’s better to limit yourself to less and do it well and properly than to get bogged down with too much until you literally „outgrow everything“. But — also to you, dear Birgitt — I will try my hand at a first window sill next year. In the most inconspicuous place to see how the neighbors react (24 balconies in the house and only three planted, one of them with geraniums). If there are no negative reactions, the rest will follow. Thanks again and again to everyone for your great commitment and your good tips!
Kind regards,
Maja
Dear Maja, thank you for your detailed feedback. That was exactly the point of the lecture and is certainly also the point of Birgit’s many congresses and her „Vorbiogrünbalkonern“, that many possibilities are shown and what needs to be considered so that everyone can choose for themselves, inspired by many experts, what suits their situation best, what they feel like doing.
Another tip from my „practice“: put up a notice (with a small flower/insect photo) in the house and inform people about the sense of greening cities and that you also want to make a contribution on your balcony and ask whether there might be someone who is interested and would like to exchange a few thoughts about it with you (over a cup of tea or coffee?). Perhaps someone with concerns will get in touch. Then it’s very helpful to address these fears and work out together what solutions are available, from knowing the facts to protecting them.
In most cases, the solution is that the person with concerns feels heard and knows that they will find a sympathetic ear if they are „disturbed“ by your future balcony growth. Empathetic communication always helps!
And another thought: the balcony was too small for me and I started sowing Stagetes, marigolds, columbines … along the fence outside and enjoy the flowers and insects when I get home.
Have fun and good luck with your greening campaigns“
Sincerely, Anke