David Quail tells how his seed-raising methods, explained in a previous article (BCSJ Vol. 15(1) 1977) have changed and developed in the intervening period.

There is tremendous interest at present in the slower growing cacti, and in particular the genus Ariocarpus.  This stems from a number of factors, including the realization that they are not particularly difficult to grow, the exciting recent discoveries of new species, and the growing availability of seed raised plants, which is important as these are all CITES 1 plants and the flow of legally imported habitat plants has ended. The interest has also been fuelled by a number of recent articles, in particular an excellent suite of them in the US Cactus and Succulent Journal, Volume 71, No. 4 (July-August 1999), almost the whole of which is devoted to this genus. There is also a very informative website (www.living-rocks.com) devoted to the genus.

This article results from my continuing interest in these slower growing plants, particularly the Mexican ones, and in my quest to develop a reliable method of producing seed raised plants in volume.  Inevitably, the techniques described in my previous article have been developed and refined since then, and we have also moved house, which has provided opportunities for improvements.  In particular, our new house is situated on a south-facing slope and we have been able to site the greenhouse in a position where it can receive sunshine all day, summer and winter, whenever the clouds, which have a habit of congregating over the Pennines, decide to move off elsewhere.

However, in spite of the sunnier aspect, which is of tremendous value in the later growing-on stages and in ensuring that the greenhouse is normally very warm, seed germination and the early years of the seedlings' life still take place in a propagator with artificial light.  This is because the English weather is too variable to give good results with these slow growing plants using natural light, which is too strong when sunny, and too weak on dull, grey days.  In my previous article I described how I had commandeered the top of our airing cupboard as an excellent propagator, but in our new house my wife was, unfortunately, one step ahead of me, claiming squatters' rights on behalf of the legitimate storage of linen, and I was forced to look elsewhere.  In fact I had already extended my propagating facilities beyond the airing cupboard, so my new facilities are centred round these alternative facilities.

My main propagator for germination is now situated in the greenhouse, and consists of a wooden box, 1.32m by 0.82m, made of 12mm plywood, with no bottom, and removable panels at the top.  It sits under the staging, on two sheets of expanded polystyrene, each 22mm thick, for insulation, and there are removable sheets of polystyrene to put round the sides and on top for winter. Along the top are two wooden bars on which are mounted double fluorescent light units, 4 feet long, and the rest of the top is removable for access.  The only heating is an air-warming cable which I use just in winter during periods when the lights are off. At other times sufficient heat is generated by the lights.  Both the lighting and the heating are controlled by time switches and the lighting is set to come on for 12 hours daily  On hot days in summer I need to open the top a little to let out the excess heat. With this approach a temperature range of 62°F (17°C) to 95°F (35°C) is maintained, although in the first three months of germination I try to maintain a minimum of 65°F (18°C) by keeping the side and top insulation in place when necessary.

I also have another propagator which has bubble polythene sides, a triplewall polycarbonate top, a soil warming cable and lighting by means of both natural light and fluorescent tubes, again worked on a time switch which gives equally good results. Again this is situated below the staging, but in a position where, unlike the other one, it receives much more natural light, including the early morning sunlight.

Whilst warm white tubes work very well, an electrician friend suggested trying a tube which had been developed for the retail clothing trade, so that lights in shops showed correctly the colour of the clothes which customers were buying, and are therefore closer to the normal daylight spectrum.  These are called Polylux XL tubes, and can be obtained reasonably easily from lighting specialists.  They are a little more expensive than warm whites, but not prohibitively so.  One particular advantage is that they put out more light per watt, and consequently the number of tubes used in the propagator has been reduced from 4 to 3 without any adverse effect on growth.

Most of the seedlings are grown in half trays, as smaller containers are more prone to drying out. These are enclosed in watertight polythene bags, with the open end tightly sealed with a freezer tie, to stop any moisture escaping. To stop the bags collapsing onto the soil surface, two pieces of wire are fastened to the sides of the trays. The bags are then tightly packed in the propagator, and need virtually no attention. During the year after we moved house, when there was a distinct shortage of time to attend to the seedlings, they were only looked at, and where necessary watered, twice during the whole year. Whilst this is not to be recommended, in fact all were growing well and in no way suffered from this neglect.  Normally however I aim to inspect them monthly in case there are any attacks by pests or fungi, but they usually only need watering if a bag has a hole in it or the freezer tie is not tight. In other circumstances they need watering about 6 monthly, when I usually add some plant food, such as Chempak or Phostrogen in a normal or slightly weaker than recommended solution.

Seeds are still usually sown individually, as described in my earlier article, using a small watchmaker's screwdriver and the moisture from the seed tray, which has previously been watered from the bottom before sowing, to pick each seed up and press it lightly into the compost. After sowing I now stand the tray on newspaper for about half an hour to ensure that excess moisture is removed.  Experience has shown that this is important, as if the tray is put into the bag too wet, algae and moss are more likely to form on the soil surface and the seedlings are more susceptible to fungal infections. However, if the trays are left unattended even for moment they are always covered up in case any sciara fly or other pests are in the vicinity.  Experimentation with composts has continued and the composts used are always documented for each tray and the germination results recorded, together with comments about subsequent growth rates and any problems experienced with moss and algae, pests and diseases.  This has enabled results to be reviewed and composts changed.  The main conclusions are that the type of compost used is of less importance than its consistency, and good success has been experienced with various types of compost.  In one controlled trial there was slightly better germination and initial growth using a peat based compost, though with time the samples grown in John Innes based compost caught up.  However I do not now use peat based composts because once the seed trays are removed from their polythene bags they are more prone to sciara fly infestation, so I now only use John Innes (loam) based composts.

The compost which has proved most consistently successful is a mix of about 40% John Innes seedling or number 1 compost, 25% gritty sand (around 1mm to 2mm grains are ideal with no powdery sand to clog up the compost), 25% seedling grade vermiculite, and 10% fine grade Biosorb, which consists of tiny red absorbent granules.  This mixture gives a very open and free draining compost which the fine roots can penetrate easily, with many air spaces for good root health and beneficial bacterial action.  Its openness is also less conducive to the growth of moss and algae, though I still have problems with these.  However I sprinkle on some more of the gritty sand as soon as any moss or algae appear, provided that the seedlings are tall enough not to be buried, ensuring that the sand is very dry and therefore less likely to lodge on the top of the seedlings.  Sterilization of the compost in a microwave was abandoned as it gave unpredictable and sometimes disastrous results, because both good and bad bacteria and other organisms are killed off and the subsequent recolonisation will be unbalanced and may have a predomination of bad organisms. Now I just ensure that a fresh bag of compost is used at the start of each year for seed raising, and that the other materials are kept clean and dry.  I do not now use any insecticides or fungicides preventively and have rarely had any subsequent problems.  It has occasionally been subsequently necessary to use a fungicide if there has been any rotting off but there may still be a case for preventive watering with fungicide to kill any spores on the seed coats.

For the very slow growing seedlings, like Ariocarpus, Aztekium, Geohintonia, Encephalocarpus, Strombocactus, Turbinicarpus, Obregonia, Blossfeldia and Pelecyphora aselliformis, I now keep them growing all their first winter in the propagator, and only bring them out into daylight in the summer of their second year, so that they have been growing continuously, with no variations in lighting or heating conditions, for between 15 and 20 months.  This technique has also been used very successfully for other temperamental seedlings like Discocactus horstii.  All these types grow absolutely typically, do not etiolate, are a nice dark green colour and acclimatize well to subsequent daylight conditions.  In fact one seedling of  Ariocarpus agavoides which had been grown in this way for nearly 18 months and was put out into the daylight in August responded to the shortening of the days which ensued during September and early October by flowering about six weeks later at only 19 months old!

When the trays come out of the propagator, the polythene bags are removed, the soil surface is covered with gritty sand or small granite chippings if this has not already been done, and the plants are placed in a propagating frame either on, or in a sunny position under the staging.  The frame consists simply of a polythene enclosure with no additional heat, but the polythene filters the light, keeps the atmosphere a bit more humid, stops the compost drying out quickly and raises the temperature.  They may stay in the propagating frame for two years or so before being moved into the open greenhouse.  One thing I have learned about these slower growing plants, particularly the Mexican ones, is that they like heat and lots of it, but when young, only filtered light.  On hot sunny days, when the temperature can sometimes be well into the 90s Fahrenheit (+35°C), if the soil is moist, you can almost see the seedlings growing - and don't forget I'm talking about plants like Ariocarpus here!  Any talk of these plants not needing much moisture, either as seedlings or mature plants, is nonsense.  When it's hot they need a good soaking, preferably from below, and a free draining, open compost, and with this treatment they will deform their pots or trays with the swelling of their tap roots surprisingly quickly.

Whilst I start off many of my other seed sowings of the faster growing cacti and succulents in the propagator, these are removed after between three and six months into natural lighting conditions. Some seeds, particularly of Opuntia, Aloe, Agave, Yucca, other larger growing succulents and Lithops are germinated and spend their first few months either in the open greenhouse or on a windowsill, still enclosed in polythene but with no extra heat or shading.

There is no rush to prick out or pot on, as the closeness of the plants keeps the compost moist and speeds growth, and the plants are usually quite tightly packed before I do so.  However, the openness of the compost ensures that when I do, the old compost falls readily from the roots and they are not difficult to untangle.  The compost used next is closer to my normal compost, and consists of about 40% John Innes No. 2 or potting compost, 20% small chippings, 20% gritty sand (normally washed river sand) and 20% perlite.  For the chippings I normally use granite, but for the slow growing Mexican plants, which mainly grow in limestone areas, I have started using limestone chippings instead with good results, and also add a little ground limestone (granules, not powder) to the compost. However, I do not use any limestone for the first, seed sowing mixture, though I may carry out experiments with this later.  Because my seed germination results are often quite high, and may exceed 80% if the seed is good, and as subsequent seedling growth is acceptably fast I have been in no rush to change the proven recipe.  However, initial results of growth at later stages with the addition of limestone look promising, and in some cases dramatic, though I'd like to see them over a longer period before getting too excited.

Once the seedlings have been transferred to natural lighting their winter treatment is as for all the other plants.  Watering stops around the end of September, and the plants are then kept dry until a suitable sunny day in March or early April, after which regular watering starts again.  I try to maintain a minimum winter temperature of 40°F (4°C), but on cold nights it can go lower, though not below freezing.

Seed raising is a tremendously satisfying activity and with artificial light can be started in the depths of winter when little else is happening in the greenhouse.  In this way it makes plant growing an all year round activity.  The seeds of the slower growing plants are readily available from the many excellent seed suppliers, and don't forget to pollinate your own plants so that you have another plentiful source of seeds.  So what are you waiting for?  Do something positive for plant conservation — sow some cactus seeds today!

Illustrations: (Will open in a new window)

• Fig 1:  Obregonia denegrii seedlings  - 7 months old

• Fig 2 :  Aztekium hintonii seedlings - 13 months old

• Fig. 3:  Aztekium hintonii seedlings - under 5 years old

• Fig. 4:  Ariocarpus fissuratus seedlings - under 4 years old

• Fig. 5:  Pelecyphora (Encephalocarpus) strobiliformis - under 3 years old

• Fig. 6:  Ariocarpus retusus subsp. retusus (furfuraceus) in flower at around 8 years old

• Fig. 7:  Ariocarpus (retusus subsp.) trigonus 'var. horacekii' flowering at under 5 years old.

• Fig. 8:  Ariocarpus agavoides seedlings flowering at under 4 years old

• Fig. 9:  Strombocactus disciformis seedlings - around 7 years old

• Fig. 10: Ariocarpus bravoanus subsp. hintonii - under 5 years old

• Fig. 11: Ariocarpus kotschoubeyanus var. macdowellii seedlings in flower at under 5 years old