Sunday, September 30, 2018

Lithops cultivation on a windowsill (16 pics)

Recently I realized that after almost 10 years of writing about growing lithops and other succulents under less than ideal windowsill conditions I do not have a single post here that would summarize the whole endeavor. Let me try writing it all down now and if I miss something comments are always appreciated :)

Full disclosure. My approach is not scientific, I do not know the pH of the substrate nor do I note the average air temperature throughout the year. The experience I've gathered is based on close observation of the plants and learning from my mistakes.
Update January 2019: Winter temperature is 13°C at night and 16°C during the day. Summer temperature in the sun goes up to 48°C.

1. The windowsill

There are some things you need to know about my windowsill: 

- It is quite spacious, measuring 0.6 x 2.5 meters. Currently I have 4 trays of plants there with several pots standing free. There is room for the 5th tray but I like to have some free space as I do my sowing and repotting (and my cat does her sleeping) there as well. The trays are 40x60cm and contain 77 containers each. I also use the spaces in between trays for shallower pots with younger seedlings and such.
- It has window panes on 3 sides, not just one, thus allows just a little bit more sunlight in during the day. The longest period of full sun exposure is between 6 am and 2 pm in Summer, which is not nearly enough. It's much much less than that in Winter (if the sun comes out at all). There are spots on the windowsill, behind the non-glass parts of the windows, that have more shade. I use those as well, in rotation, for example for sleeping conophytums or rooting adromischus leaves. No free spot stays unused.
- It is directed somewhat South-East, I believe. Meaning, when the sun rises it first appears straight and slightly to the left. Bear with me, I'm really not a scientist.
- I do not use any artificial light. The light the plants get solely depends on the weather.
- I do not use any fans, nor open the windows. The windowsill is in my living room, separated from it by Florentine tulle. Whatever air circulation happens naturally (probably caused by me running around) it seems to be enough.
- I do not manipulate the temperature in any way. In Winter it has about the temperature of my living room (I do not heat during the day when I'm at work). In Summer the temperature rises up to 48°C when the black pots get too hot to be touched. There was never any sunburn related damage on the plants that I can recall, probably because the sun moves on from the windowsill by 2 pm.

As you can see, the above describes the general conditions, constant value, on which I have no influence.

So what are the points that we actually can manipulate? What is it we can do to compensate for all the unforeseen weather-related hardships of our lithops and help them be their best selves?

Here comes the No 1 Rule for growing lithops on a windowsill: Keep your plants as small and flat to the ground as possible. Your goal is - by all means necessary - to prevent them from growing upwards, also known as stretching. The slower they grow and the smaller they stay the healthier and prettier they will be and the longer they will live. All the care you give them should have this as a goal. You can achieve it by controlling what substrate and pots the plants grow in and by restrained watering. 

2. Substrate and containers

The substrate I use is pure pumice or pumice sand. There is absolutely no compost in there nor perlite or aquarium gravel. The size is often referred to as 0-2 mm but what it is is small pumice stones with pumice sand. Both Kakteen-Haage and Cono's Paradise sell it, if you're in Germany/EU, but it is also available on eBay or in stores specialized on bonsai. I tried Akadama, by the way, and it was a bad idea (the stuff they sell here is full of chemicals and slime). Do not use lava stones with holes in them for decoration either or you will never get rid of mealy bugs that hide in there. And if you use decorative quartz as top layer you will not be able to know whether your plant already has been watered recently or not and will keep watering it unnecessarily (believe me I know). In short, it's all pumice, all the way. Below is how slightly moist pumice looks like straight from the bag. I do not wash or microwave it. I only microwave the pumice I use for sowing (650 watts/1 kg/3 min).

You know how lithops like to rot? In pumice it rarely happens. The way it works so well is that the plants don't get "wet feet". Pumice does not retain moisture in a way compost does, making a swamp. Wet pumice, while sucking in water, does not let the roots actually be "in the water". The roots are semi-dry (no swamp) while the plant can still pull the moisture out of the stones when needed. This not only prevents rot but also is a safeguard against overwatering because it dries quicker. One wrong watering (that's often all it takes for your plants to start stretching) in pumice is less likely to be as dramatic as in other substrate. I refresh the substrate every 3 years or so.
It is also important that when you buy a plant that's already in a pot, you immediately pull it out, wash it, let it dry and transplant it into dry pumice where it will stay unwatered for at least a week. Even if you buy a plant from a specialized nursery and think that they use appropriate substrate and want to keep it - don't. What works in a greenhouse will not work on a windowsill. Any trace of plant food or compost will lead to stretching when there's not enough light to support the boost of growth (see No 1 Rule). 

For adult lithops plants I use square plastic containers (with drain holes of course) that measure 5x5x8.5 cm. Anytime I tried something bigger I lost the plants to overwatering. You have no control in bigger pots. 5x5x5 cm pots would work very well, too. Lithops roots go deep though and the depth of 8.5 cm seems to be good for them. Kakteen Haage and Kakteen Schwarz (wholesale) in Germany offer them. The main thing is that the pots are small and you squeeze as many plants (of the same species and age/size) in one pot as possible without them touching each other. One-plant-per-pot approach is for greenhouses.

It is not only space-saving but also another overwatering safeguard. What one sleepy lithops cannot drink up, its neighbor will; what one greedy lithops could have consumed all by itself, it now has to share with others - no rotting roots and no stretching. Normally I have 4 one-headed plants in one pot or 2 two-headed. Below are 4 two-headed plants happily living in a 5cm pot. I can squeeze up to 16 seedlings into those 5 square centimeters - it only does them good.
Also, use plastic, not clay. It dries quicker, is lighter and transplanting is much easier - just squeeze and pull. Thank me later.

3. Watering

This is the most tricky part. And the most important. You will have to summon all your power of observation and self-control to figure it out. Here are some pointers.

The first thing to remember is that once a year lithops need to change their leaves. The regeneration is a long process that takes several months to complete and during which old leaves completely dry up while the new leaves feed of them, recycling all the moisture. Unfortunately lithops are opportunistic and don't know what's good for them. If water keeps coming old leaves will never dry up and then stacking begins. At the end the new leaves choke on the old ones and the plant stretches, rots and dies. So much for the background.
Our task is now to support the regeneration. In northern hemisphere it means to stop watering completely mid- or late October. The last splash of water comes with a wilting flower. Once you stop watering the roots will become inactive and the old lithops leaves will get wrinklier and wrinklier. This is exactly what we want to see. Winter is a period of active growth, in fact - underneath, deep inside the plant, the new leaves are growing. The wrinklier the old leaves, the bigger the new ones. Around April the old leaves will be gone and the new fresh leaves will emerge. It can be earlier, it can be a bit later. This indicates that you can start watering again. If the old leaves are digested earlier it's better not to start watering until the weather stabilizes (many consequent sunny days). If the old leaves are not fully digested until June, cut off what's left of them and pretend they are. The roots will quickly re-grow and the plant will react to water after the second watering at the latest.

The second thing to remember is that between April and October you can not water by schedule. There is no schedule like "water all your lithops every two weeks". Now your power of observation comes into play. You look at every each of them, one by one, and decide which one gets watered and which one doesn't. Just looking is not enough, you also have to touch them. If they are wrinkly and soft (sometimes even hiding in the stones) - you may water. Otherwise you may not. When in doubt - don't water, re-evaluate in a week. Sometime during a Summer heatwave you might notice that the plants are wrinkly but hard as a stone. They are resting and no water is needed then. This is supposed to encourage flowering but who knows. Flowers on the windowsill are an exception, not a rule.

How much water do I give them? To illustrate, this is the watering can I use. For watering of one pot, no matter how many plants are in it, I use half of it.

I do not fertilize. Because I always forget. When I do remember, I do it in August or September. The beginning of the year feels too risky (stretching).

4. Sowing and seedlings

You guessed it, I use the same place and the same substrate for sowing. All my plants live together on the windowsill, including newly hatched seedlings. The difference is that I microwave the pumice before sowing and use 4x4x4 cm small pots (mainly because 20 of them neatly fit into my mini hatchery, formerly known as "jewelry box"). Bigger Ferrero Rocher boxes work well for sowing, too.

The method is simple: label the pots, fill them with pumice, make it wet, spread seeds on top, cover with a transparent lid and wait. No artificial light needed. You should sow either in February or in September though, when it's colder. In my experience germination starts one week later. Sometimes I get new seedlings after one month. Don't get discouraged. The "3 days" info you find online is fairly unrealistic. For the first few months the pumice surface should stay moist at all times. It does not mean you need to spray every hour. It stays moist automatically because the lid is on. Keep the seedlings under the lid until you feel they are strong enough to move out or be transplanted. Wait until the first true leaves to be on the safe side (about 4 months).

You will see a significant change in their surface structure after the first leaf change. It will be much firmer and stronger, it might already have some color that will keep them safe from strong sunlight.  It's safe to remove the lid and let the pumice surface dry between waterings now. From there the care is basically: when you see them shrivel a bit, give them water, all through the year, even in winter. They are not on the yearly leaf changing schedule yet and will regenerate whenever they like, several times a year. It's how they grow.

This is how they will look like after 2 years. Yes, if they are at this size (4 mm?) you're doing it right. After two years they should be close to the yearly lithops life cycle and at the age of 4 they should start looking like adult plants. Do not believe the info online that they will flower when they are 3 years old. Can you imagine these tiny kids flowering? In a year they won't be much bigger.

Be patient. This year the seedlings I grew from seed 10 years ago are flowering for the very first time. And oh how rewarding this is!


  1. Excellent post. Thank you for writing it down.

  2. Amazing post!!! thanks for all the info!!!!! <3

  3. Thank you for this--and thanks for this wonderful blog! Sooooooooo much info and data and lovely pictures and beautiful reflections. It is why blogs were invented, I think!

    1. Thank you very much for stepping by and reading. I'm glad you enjoyed it :)

  4. Hello Rika. That is a lot of material to digest, so I will comment on each section in a separate comment entry. Thus, I will begin with the 1. Windowsill section. The fact that your lithops look good and you have been growing for a number of years indicates your light is satisfactory for lithops. This is important because it is generally assumed light is the most limiting factor in growing succulents in general on a windowsill. However, there are two aspects of lithops growing that also should discussed. One, are you satisfied with the flowering performance of your plants? Two, are you satisfied with the growth rate of your plants? Whether either, or both, of these factors are important will of course depend on the desires of the grower. A commercial grower. for example, would be very concerned with the growth rate because they would want to grow saleable plants as quickly as possible. Many hobbyist, not necessarily all, would want their plants to flower. Therefore I believe both flowering and growth rate should be considered in terms of evaluating any growing environment, including windowsills.

    While light intensity is probably the most important environmental factor in evaluating suitability for growing lithops, I also believe temperature plays a potential role. While for your windowsill environment there doesn't seem to be problems with extreme high or low temperatures, it is possible in other windowsill environments this could be a problem In my windowsill environment I have noticed as much as a 12 degree C drop in temperature at a point within 15 cm of the window compared with the room temperature. This does not seem to be the case with your windowsill but it can occur in other environments and thus questions how low a temperature is detrimental for lithops.

    Finally, for most plant growth, it is often desirable for there to be a noticeable differential between daily high and daily low temperatures. In nature this usually involves a higher daytime temperature than night temperature. For many plants this day night differential seems to stimulate growth. There is currently no research information on lithops concerning ideal daily temperature ranges. This is understandable because lithops are not considered a commercially important crop and do not warrant such research. In fact, your observations and records are quite unique in understanding lithops growth under hobbyist conditions.

    I'll try to write again soon and take a look at your comments on substrate and containers. It is great to see someone interested in sharing what they have learned in growing these great plants with others. Bob

    1. Thank you so much for your feedback Bob. Let me come back to you on this this weekend :)

      (Sorry I've been kinda absent lately...)

    2. Hi Bob :)

      Sorry for replying to you so late. Life got in the way somehow.

      >>>One, are you satisfied with the flowering performance of your plants? Two, are you satisfied with the growth rate of your plants?

      You're right, I should have commented on this.
      While the light on the windowsill is enough to grow plants from seed and to keep them alive and in good shape for many years, it is definitely not enough for reliable flowering performance and for growth rate needed for commercial sale. This is just the reality of windowsill growing. Those for whom flowering and fast growth is important should definitely use another environment (greenhouse, artificial light etc.). For windowsill cultivation those factors are not really relevant (I'm not producing seeds and plants for sale) and I did't feel it worth mentioning at the time :D Especially since, while flowers are welcome, they are very far from a priority for me personally. And the fast growth just means I run out of space too quickly. Running out of space is already a big issue for me. Those fast growing Anacampseros are killing me :)

      >> I also believe temperature plays a potential role.

      >> In nature this usually involves a higher daytime temperature than night temperature.

      I need to pay attention to that more. Recently my parents visited and my mom said "Hey, if I stretch my hand to touch your plants, the air is so much colder there!!" I myself never noticed that. Let me measure the winter temperature and report on that.

      Thank you very much for reading and for your comments. I'd be very interested to read your thoughts on the other aspects as well if you find time to write :)

  5. Thank you! Very useful information.

  6. Hello Rika, wonderful reading and lot of helpful tips. I have a question and cannot get any answer from seed supplier. My seedlings are now almost 5 weeks old, still in the bags with high humidity. When should I take them out of there? I am trying to ventilate them daily, by opening the bags. have searched at the internet for weeks now, but cannot find any information about how to handle the seedlings after germination. Many thank in advance! Kind regards, Airi

    1. Hey Airi! Thanks for reading :)

      You can check the section "4. Sowing and seedlings" above. I'm writing about it in detail there. When I say "lid" that's the bag cover you use. Just continue the ventilation as you do. If there's no mold or algae in the bags no need to change the setup.

  7. Do you have any problems with gnats or fungus? I've just found your blog and already you've help me. I'll be watching and rereading all. Many thanks for your time.

  8. Hi Peggi. Thank you for visiting! I'm happy to help :)
    I haven't had any gnats infestations and didn't see any fungus on my plants. There are sometimes algae in the seedlings pots though.
    If you have any other questions please feel free to comment. I receive notifications of new comments and will get back to you asap.

  9. Hi Peggi. Thank you for visiting! I'm happy to help :)
    I haven't had any gnats infestations and didn't see any fungus on my plants. There are sometimes algae in the seedlings pots though.
    If you have any other questions please feel free to comment. I receive notifications of new comments and will get back to you asap.

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  11. Only pumice
    Do you use fertilizer for lithops?

    1. I practically do not fertilize. Maybe once a year. Maybe not at all. Don't remember when I did it last....