When to pricking out cactus seedlings, how to do it correctly, and what potting soil to use

Astrophytum asterias mie semine svasate in fila

Speaking of cactus sowings, a classic question, and one not infrequently asked with a fair amount of (unnecessary) apprehension, is: after how long should seedlings be repotted? In other words, when do the young seedlings need to be repotted and perhaps divided into individual pots? Again, as with many other “cactophilies matters”, the answer depends on various cultivation factors. Based on experience, however, it is possible to give general indications useful to those who experiment with sowing for the first time.

Let’s see in detail, in this article, everything we need to know about this fundamental step for the proper growth of plants from our sowing. (…)

Astrophytum asterias mie semine svasate
Astrophytum asterias seedlings

Granted that for everything related to the sowing of cacti and succulents, whether in natural light and heat or in a propagator, you can consult the various articles contained in the appropriate section “Sowing” of this site (you will also find a photographic tutorial), the subject at hand is correctly called “pricking out”. This term indicates the division and repotting of seedlings in single pots or in usual boxes, thinning the space between one plant and another to favour and accompany the growth of individual exemplars. The moment chosen for pricking out is fundamental because this can depend on the proper continuation of the sowing, with the plant developing robust and well-formed specimens. In fact, if you keep plants too long in the sowing containers, they consume the space and the soil at their disposal. Their roots can’t expand, the stems touch each other until they deform due to the pressure exerted by the growth, and in many cases, plants with a globular shape can take bizarre forms, oblong, squashed. In short, deformed. Above all, if you leave seedlings too long in planting containers, they grow more slowly, reach a size and then stop, merely surviving.

When to prick out
Astrophytum asterias mie semine svasate
Repotting my Astrophytum asterias

Pricking out is a field that does not escape the subjective sphere. In other words: some decide to prick out a few months after the birth of the plants when they have begun to form their first spines, and those who wait at least a year, if not two. I have read that early repotting, only six months after birth, would make the seedlings grow faster. However, it must be said that so young specimens can easily suffer because of a repotting not done with all the rules. Personally, even if many plants have germinated in the same pot, I wait at least one year before pricking out. Considering that I only sow in natural light and heat at the end of March or beginning of April, I let the seedlings complete a life cycle. Spring, development in the warm months, slowing down in the summer months, stagnation in winter at low temperatures and watering suspended from October to March.

When I prick out my seedlings in March or April of the following year, I am dealing with generally well-formed specimens with stems of some consistency and partially characterized spines. Above all, I am dealing with plants that have a well-formed and branched root system. This is true for the vast majority of cacti, although there are genera whose plants need at least three or four years before they reach a “manageable” size, such as Aztekium, Strombocactus and Blossfeldia.

In some cases, for example, if a few plants have sprouted in the same container and are therefore well spaced out, I wait a couple of years before pricking out. However, I often fertilize because I use poor soil for sowing and containers that are not particularly large or deep.

How to proceed
Astrophytum asterias mie semine svasate
Astrophytum asterias: roots

The pricking out procedure does not imply any particular difficulty, as long as you have patience: in my opinion, dealing with plants half a centimetre or so is not the most fun. It’s also necessary to be very delicate because the stems of young plants can be easily crushed if wrongly handled, and the roots must be treated with extreme care.

The cases can be basically these two: you can prick out more seedlings in larger containers, thus thinning the plants and giving them more space; or you can prick out seedlings at least one or two years old in single pots (in this second case, we can already talk about repotting proper).

If the seedlings are still little and we choose to place them in a larger container, such as a plastic tub, or a wide and low pot, first we have to gently extract the seedlings from the vase and divide them by cleaning up the roots slightly. At this stage, we can use a stick or the spoon’s handle to lift the seedlings out of the pot and extract them. When the roots are roughly cleaned, we place the plants in a container and leave them for four or five days in the air (but not in the sun). In this way, any cuts on the roots can heal. When we are ready to prick out, we prepare the container by filling it with soil, at least one centimetre below the edge. At that point, using a pencil or a stick, we make holes in the loam and then slide the seedlings in. At the end of the job, it’s enough to top up with a little potting soil, tap the container lightly to let the substrate settle and sprinkle the surface with gravel or quartzite to guarantee stability to the plants until the roots, growing, don’t have “welded” them to the ground.

Astrophytum asterias mie semine svasate
A. asterias: young specimen

If the plants are already sufficiently formed to fit in single pots of 5, 6 or 7 centimetres, we will proceed in the same way, with the only difference that we will place each plant in its pot as we do with adult plants, i.e. holding them by the stem and inserting the soil with the help of a shovel or a spoon. In both cases, pricking out or repotting in individual pots, it’s best to use the same type of potting soil that we would give to that of a plant’s species if it were an adult. In other words, if we usually use a mix of equal parts pumice, lapilli and peat for that plant, that’s our pricking out soil. For slow-growing plants, even more so, it is advisable to use a substrate with at least 20% organic matter (peat or earthworm humus) to aid growth in the early years.

How to prepare the proper substrate for cacti and succulent plants.

Pay particular attention if you have decided to use marl for pricking out your seedlings (e.g. for Ariocarpus, Pelecyphora, Epithelantha, etc.): with young plants, it’s recommended do not to exaggerate, and it’s better to use a maximum of 30% (aggregates and peat for the remaining 70%). Higher amounts of marl, I state from personal experience, can inhibit or slow down the growth of young plants up to stop it altogether.

After pricking out
Astrophytum asterias mie semine svasate: radici
A. asterias ready for the new pot

Once the work is done, the plants can be treated like any adult cacti, i.e. no watering for at least two or three weeks (if you prick out in the winter as I do, the problem doesn’t even arise) and gradual exposure to light, but avoiding direct sun until the plants are at least three or four years old. One or two-year-old plants require slightly more frequent watering than adult plants. Let’s say that in the warm months, you can get to water every 5 or 6 days if the soil dries quickly. In this way – by increasing the frequency of fertilization a bit – we will help the seedlings regularly grow without having “pumped” and phoney plants.

Astrophytum asterias mie semine rinvasate
A. asterias: young specimens after repotting

In the photos completing this article, you can see the procedure described here applied to some of my Astrophytum asterias seedlings. In this case, we have plants at least three years old, at their second repotting after the first pricking out in low square pots. Within a couple of years, the roots had already deformed the containers as they developed. Interestingly, some specimens (only a couple, to be honest) remained much smaller than others. From what I have observed over the years, this depends on the space that the roots “take”: if a specimen, for genetic reasons or because it is less stressed by repotting, is faster and more responsive, it colonizes the pot first, taking away space and soil to other specimens, which consequently suffer slowdowns in growth. Nothing irreparable: after the plants have been divided and planted in single pots, the increase starts again in the same way for all of them, and the small ones recover the lost time without particular problems.

If you want to learn more about the Astrophytum genus, here is a specific sheet.

Correlated articles

Six identical cacti in three different soils
How to repot cacti and succulent plants
Substrates for cacti and succulents
The correct soil: the materials you can use

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