To those wondering to what extent the substrate affects the growth of cacti; for those wondering if natural gypsum (also called agricultural gypsum) can be useful in the formation of robust thorns, this article will certainly be useful. Article which is nothing but the update of a small experiment – one of the many I do with my plants – which I started in July 2020 and which gave surprising results, amazing me first. Yes, because although the test sample is limited (six plants in all) and the results are therefore to be considered indicative and far from absolute, I must confess that I did not expect such a response just over two and a half years after the start of this test. It is known that substrates can literally make the difference in the growth of cacti and that natural gypsum (at least with some species of cacti) is an exceptional element, but it is with direct evidence, with the experimental method that we can really appreciate the impact of the soil in the growth of our succulents.

In this article, therefore, we go into the details of the experiment and see, after more than two and a half years, the results I obtained, which in my opinion are remarkable. (…)

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L'articolo Identical cacti in different substrates: extraordinary results of my test and the surprise of natural gypsum proviene da Il fiore tra le spine.

The real unknown factor is represented by the two Mammillaria in the unedited soil, very rich from an organic point of view. We will see over time how their growth will be affected by this substrate. With this consideration, exactly one year ago, I concluded my article on one of the experiments that I do from time to time on cacti and succulents. In the specific case it was a test with three different substrates, in fact three types of “soil”, in which I repotted six Mammillaria hahniana obtained from a single sowing.

After the first year of cultivation, here’s how the experiment is going and here are some initial considerations. (…)

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L'articolo After one year of cultivation, the first test results on six Mammillaria in three different potting soils proviene da Il fiore tra le spine.

Instead, the aim of “wild” cultivation is to obtain specimens as robust as possible, and with the same look to those that grow in the habitat (I write about this cultivation’s philosophy here). In addition to the documentation and possibly travel to observe the plants in nature, it is essential to engage in some experiments and be willing to question continuously, even if it could lose some specimens (not the valuable ones, of course). (…)

One of the fields in which we can experiment the most is that of substrates (or potting soils). If it is true that the growth of a plant – in our case cacti or succulents – is influenced by an infinite number of factors such as exposure, temperature, watering, fertilization, etc., it is also true that the substrate is one of the elements on which we can most “indulge” to test the reactions of plants and, consequently, their growth to note everything and draw useful conclusions. Without going into the details of succulent potting soils (here you will find a series of articles dedicated to this topic), I summarize in this post a simple experiment that I have done in recent days, also related to some other “tests” on substrates that I have done over the years with other species of cacti.

It all stems from a simple visit to the local nursery in June to get some products commonly used for the greenhouse. Among the succulents that had recently arrived in large quantities from the Ligurian Riviera – common plants for a euro each – I noticed a whole plate of Mammillaria hahniana. I generally don’t buy cacti from non-specialized nurseries, and in recent years I’ve cut back on purchases considerably, preferring to sow my own plants. However, the Mammillaria were beautiful and, like all “white” Mammillaria, interesting to me. Those seedlings, about two years old, definitely came from the same sowing: they were, in fact, of identical size (a couple of centimetres in diameter), all similar and grown in the same small pots (2.5 cm). They were cultivated in pure peat-based potting soils, like almost all plants from large production nurseries, but well-formed and proportioned, i.e. not yet over-pumped by nitrogen-based fertilization, to speed the growth. Young, same-seeded plants are perfect for experimenting with different potting media, because the basic genetic makeup is shared and the young age means that the plants have grown in identical conditions up to that point, without developing significant differences due to, say, different watering or fertilizing regimes, exposure, and so on.

I decided to buy six specimens to start a test, even though June is not a time for repotting by my standards. On the other hand, I haven’t planted for a couple of years and having six Mammillaria to learn something new from seemed like a good opportunity, even though I have done some testing with other Mammillaria species in the past.

Once I got the plants into the greenhouse, I unplugged them and freed the root system from the pure peat they had been growing in. The peat was soaked, and I helped myself with a jet of water to thoroughly clean the roots removing any residual soil. Of course, during this operation, the peripheral rootlets went away with it, but this will not create any problem for the plants, which are young and healthy and will quickly rebuild the root system. Once the roots were cleaned and evened out, I placed the bare-root plants on a Styrofoam base and left them in mid-shade, directly in the greenhouse, to dry. The plants stayed in this way for seven days, and even though we are in the period of full vegetation, the stem did not even hint at deflating. After a week, with the roots perfectly dry and healed, I repotted the six Mammillaria. To avoid differences in growth influenced by the containers, I used pots of identical size for all six plants (also because the plants and the roots were of similar size): I chose square ones of 8 cm side, large compared to the stem and the root system but not disproportionate. If the growth respects regular rhythms, the Mammillaria can remain in these pots for at least 3 or 4 years without problems.

As for the potting soils, I made do with what I had available at the time. Unfortunately, this year I ran out of marl that I get directly from an area a couple of hours from home and had to give up a substrate that always works very well with white Mammillaria… To give reliability to the test, I placed two specimens for each type of soil (even more reliable results would obviously be obtained with higher numbers): I repotted two plants in a classic mix of pumice/lapillus/peat in equal parts; other two I planted in a substrate made of clay soil (30%), earthworm humus (10%) and aggregates such as pumice, sand and river gravel. On the last two specimens, I made a test completely “blind” (perhaps it would be better to define it “criminal” …), creating a soil never tried before, made “by feeling” trying to balance some elements.

I used three parts of earthworm humus (cow manure transformed by the action of earthworms) as an organic component, then I added two of pumice of small particle size (pumice is the “wild card” material to make the substrate draining and absorbs water by releasing it gradually). After that, two parts of natural gypsum (or “agricultural” gypsum, used as a soil conditioner to correct soil pH) and finally three parts of ordinary river gravel (a “pure” inert material useful for drainage and loosening the soil). As “part” I mean a scoop filled with material. In this way, I can quantify the ratios between the various materials that make up the final substrate, and understand if the healthy part is enough compared to the coarse, if the organic one is a minority or not compared to the mineral, etc…

Here is an in-depth look at the individual materials we can use to create substrates.

For each pair of plants, I have matched two cards of different colours on which I noted in pencil the composition of the soil used for the test: white card for the mix pumice/lapillus/peat, yellow card for that based on field loam and a red card for the experimental one. I usually only use white or yellow tags, but in this case, by diversifying them by potting soil, I can evaluate the plants’ growth in combination with the substrate without having to read every time what I have noted on the tag. After having repotted, I’ve placed the six plants in their place, then I gave them an abundant misting to let the potting soil settle well on the surface and remove the excess dust. The six plants will obviously be grown identically to avoid that other factors – genetics and chance aside – can influence their growth. In other words, the Mammillaria will stay side by side in the same position in the greenhouse and will receive the same treatment in terms of temperature, light, watering, fertilization. Starting next spring, I will move them outside the greenhouse, in full sun: the white down will protect them and prevent the stem from burning, even if they are young specimens. Moving them now, in June and immediately after repotting, would be detrimental because the plants would not have time to acclimatize gradually and would end up under the rays of the already intense summer sun.

For getting the first results of this test, we have to be patient because time is the last determining factor in the plants’ growth. The first possible differences will be appreciated only after one or two years of cultivation. Based on my experience, I expect a faster growth of the two specimens in pumice/lapillus/peat, which will probably become wider and will tend to grow more in height than those in field soil, which, on the other hand, should remain more flat and compact. The real unknown is represented by the two Mammillaria in the unusual mix, very rich from the organic point of view and at the same time “corrected” by the gypsum. We will see with time how their growth will be affected by this substrate and the general results of this test.

Here you will find an article related to another test of mine, with the comparison between Ferocactus latispinus grown in different conditions.

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L'articolo Six identical cacti in three different soils: a cultivation test with Mammillaria hahniana proviene da Il fiore tra le spine.

Based on the experiences of some growers, plants of the genus Ferocactus seem to appreciate the addition of calcareous material in the substrate. Above all, the thorns would benefit from it, which would be significantly strengthened compared to those of specimens grown in more “traditional” soils, for example the classic pumice, lapillus, peat mix in equal parts. Based on this consideration, I wanted to make an experiment with some of my sowings of Ferocactus acanthodes (seeds obtained from a dried fruit taken from an adult plant during a trip to Arizona) and Ferocactus latispinus. The acanthodes were born in 2013, while the latispinus are from 2010. Except for the seedling soil, which was based on peat, pumice and gravel, these plants grew up in the traditional compost with 30% fine peat and the rest pumice and lapillus in equal parts. I generally use this mix when I want to help seedlings develop more quickly, and then pass them into what I consider my “standard potting soil” made of sandy clay, pumice, gravel and 10% peat.

In the following article we see exactly what my experiment consists of, what type of soil I decided to use and above all we see the results with the photos taken two years after the test. (…)

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L'articolo Strengthening the thorns of cacti: a small experiment with some Ferocactus sowings proviene da Il fiore tra le spine.

I may look like a mordant, but I want to clear the field of misunderstandings and false myths: the right soil for cacti does not exist. There are many types of soil (or composts, substrates, mixtures, the question does not change) and there are genera that prefer certain substances and others that require more. Established this and removed one of the first Faq (Frequently Asked Questions) by cacti enthusiasts to the first arms – “Which is the best soil for my cactus?” – it can be said on the contrary that on the one hand there are the characteristics that a good soil for cactus must necessarily have; on the other hand the needs of the single plants. The question was simple and the related answer was given by italian cacti expert Giuseppe Lodi, who, after observing “the butts of roots of certain imports” and having noticed how these were encrusted with clay loam, suggested a base soil absolutely natural and versatile: “You can start from a mixture of common clay loam (field or garden), coarse sand and leaf soil, in equal parts. Of these three components none of them can be enough, alone” (Giuseppe Lodi, “Le mie piante grasse” – Edagricole).

Except perhaps for the difficult availability of the loam of leaves (be careful to go for the woods and get bags of decomposed foliage: there are fines for collections of this kind), the recipe provided by the Italian pioneer in the cultivation of cacti and succulents was more than sensible, as well as experienced. Considering the difficulty of finding the loam of leaves (Lodi suggested leaves of beech or chestnut), that moreover must be well decomposed (and it may contain fungi and bacteria dangerous for the plants), this element can be replaced by good quality peat, sieved fine, without lumps and filaments. Too bad that over the years we have forgotten Lodi advice to focus everything on what for many is still the standard substrate of peat, lapillus and pumice in equal parts, standard enough to fit any kind and species of succulent.

In the following article now we see which is the best substrate for growing cacti and succulent plants based on my experience over the years with proofs and experiments on various mixtures. (…)

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L'articolo Substrate, loam, soil mix: which is the best soil for cactus and succulent plants? proviene da Il fiore tra le spine.