This article originally appeared in the January 2002 Newsletter of the Liverpool Branch

Part 1 - June 1998

Part 2 - November 2001

On Base Fertilizers and Liquid Feeding, Part 3.

by Ray Allcock

1. Introductory Remarks

The present contribution to my ongoing series on fertilizers provides at last some seriously considered and experimentally supported recommendations in regard to suitable amounts of base fertilizer, i.e. (at a more fundamental level of description) recommendations concerning the so-called strength of the compost.

The theoretical reasons for the use of base fertilizers, and the molecular mechanism by which under moist conditions they act to stabilize the nutritive strength of the soil solution, are explained in Part 1, which is to be found in our Liverpool Branch Newsletter Vol. 4 (1998) No. 3. Part 2, to be found in Vol. 7 (2001) No. 4, deals with nutritional difficulties and dangers peculiar to cacti and succulents, and provides also an account of a 3-year experiment on liquid feeding.

2. The John Innes Strength Scale

Some of the experiences on which I now draw have been obtained with John Innes Composts produced by the well-known firm J. Arthur Bowers. These I have used in admixture with grit-sand and/or gravel and/or perlite. The John Innes composts are loam-based and can be obtained in four different formulations, which in order of increasing strength are named as JI Seed (essentially of zero strength), JI No. 1, JI No. 2 (twice as strong as No. 1), and JI No. 3 (three times the strength of No. 1). The three numbered strengths provide us with an accessible and adequately defined reference scale, of practical value therefore for the description also of the strengths of various other formulations.

In the JI Seed Compost there are certain textural differences which need not concern us here, and also, while calcium carbonate and superphosphate of lime are incorporated exactly as in No. 1, the two other nutritive additives (which are dangerous to very young plants) are entirely omitted. There is also an ericaceous formulation, known as JI (A), though I have not heard of it being commercially available. It is the same as the seed formulation in all respects save one, namely that the calcium carbonate is omitted, and is replaced by an equal weight of yellow sulphur powder.

Readers seeking a source of supply for any of the John Innes composts should be warned that the name has in recent times been pirated and used to promote the marketing of loam-based products of unknown formulation and unstated strength!

Although I have sometimes used JI composts, most of my experiences in regard to fertilizers have been obtained as by-products of a long-standing preoccupation with home-made experimental loam based composts, the base fertilization of which does however admit a fairly reliable transference to the John Innes strength scale. I shall not go further into the concomitant details at the present time.

3. The Two Safety Requirements

Researchers on the pot cultivation of non-succulent plants are generally agreed (see Part 1 for a few of the various available review monographs) that the most important criterion regarding the amount of base fertilizer is that the osmotic attraction exerted by it shall not be so strong as to inhibit water intake by the roots. For the general run of adult non-succulent pot plants the highest strength consistent with this requirement is found to be No. 2, which is accordingly the strength recommended in this context. For the first transplanting or first potting of seedlings a lower strength is required, and for this No. 1 is generally taken, but something weaker than this if the young plants are soft and juicy and lacking in woody structure. For the final potting of large and vigorous subjects such as tomatoes and chrysanthemums the most usual recommendation is for No. 3, and in the case of the large exhibition chrysanthemums No. 4 is sometimes advocated. However, in view of the ready availability of liquid feeds it may be judged that values as high as No. 4 do not and can not provide the optimal answer to any nutritive problem. With this in mind it is interesting to note that the Vitax Q4 recommendation for final tomatoes and chrysanthemums comes to only 2¼ on the John Innes strength scale.

The roots of plants take in water from the substrate through two different mechanisms, both of which are affected by the state of maturity/immaturity of the plant tissues. Firstly there is the osmotic force/force of diffusion, which acts in the inward direction only if the concentration in the sap exceeds that in the soil water. Secondly there is the inward pull from the transpiration current/evaporation from the upper parts of the plant, which however requires woody microtubules to support the accompanying reduction in water pressure and transmit it down to the roots.

Since newly germinated seedlings are acutely at a disadvantage in both of the above respects it may readily be understood how it comes about that we have the long-established practical rule, that composts intended for seeds should be fertilized only very weakly, if at all. The JI Seed Compost expresses this rule by total omission of the two most dangerous fertilizing components, as already mentioned in Section 2 above. In the case of the Vitax Q4 base fertilizer (which has the advantage that it contains the necessary trace elements) a somewhat different strategy is recommended to the same end, in that the named base is used also for seeds, but only in amounts which on the JI scale range from No. 1/8 to No. 1/2, depending on the size of the seeds.

Cactus or succulent seeds sown on an overly strong substrate may germinate, but in my experience the seedlings soon become a dull dark green and wrinkled and fail to make a root, eventually shrivelling away. When therefore I read (in Haworthiad 15 (2001) p120) of successful sowings of Haworthia seed on JI No. 3, or of successful cactus seed sowings on JI No. 2 (in BCSJ 15 (1997) p16), I find myself baffled more than a little. I can only suppose that in these cases the seedlings somehow develop in a state of precarious balance adapted to a very precisely controlled environment of excessive salinity. Under more normal conditions, affected by the weather and by irrigational fluctuations, it is certainly necessary to use some very much less saline substrate, such as the JI seed compost or a compost prepared in accord with the weakest of the Vitax Q4 seed recommendations. Regular waterings with a very weak solution of soluble fertilizer (e.g. lml of the fertilizer crystals in 10l of water) will then over the course of time gradually build up the strength of the compost and the sap concentration of the plants, until eventually they become big enough and tough enough to be safely separated and replanted. Further useful observations in regard to seed composts and the use of fertilizers in seed raising may be found in my article in our Newsletter Vol. 6 (2000) No. 2.

With seed raising now to some extent sorted out (though I don't think the last word will ever be said on this subject!) let us turn our attention to plants which have progressed beyond the baby stage. With them a certain decision of policy has to be made. We can either treat them as pot plants, or we can treat them as xerophytes.

If we would all agree to grow our cacti and succulents like any other pot plants, so that their compost would never ever be allowed to dry out, then I could stop writing at this point, since I have already touched sufficiently upon the safety aspects pertaining to the base fertilization of ordinary plants.

However, most of us have no wish to grow our cacti and succulents just like other pot plants. Most of us prefer to take advantage of the unique and fascinating ability of these plants to store water and so, upon all those which grow during the longer days of the year, we impose a dry season from October or early November through to March or early April. In this way we avoid unwanted soft or unnatural growth and unwanted high heating costs, and at the same time we allow concrete expression of the interesting properties which Nature has bestowed on our pets. In the case of the short-day plants, with which we hold back on the water during the hotter months, we may discern another tangible benefit, in terms of a saving of our time and effort (though this aspect should not be overexploited, since occasional light waterings during the summer resting period do no harm, and are often visibly beneficial).

The decision to subject the plants to the droughty conditions natural to them brings with it a second and stronger safety criterion, the satisfaction of which is imperative! Any fertilized and moist compost contains nutrient ions, all of which are fully hydrated. Most of them are sitting on the microsurfaces of the solid constituents of the compost (including organic remnants), but some are sitting directly on the root surfaces. As drought sets in the ions become less hydrated, and correspondingly more electrically active. The resultant ionic attack will cause significant root damage or even root death if the ionic content is too high and the drought too severe.

We of course wish the roots to stay fully alive, as they do in habitat, so as to be ready to give an immediate response to any deluge of water. Growers who achieve this happy and worry-free state of affairs can obtain great pleasure from watching the overnight response of their plants! Equally, the absence of a rapid response to a deluge is a clear sign that something is wrong.

4. Satisfaction of the Second Safety Requirement

If the watering of a previously fully healthy non-succulent leafy plant in a normally base-fertilized compost is undertaken only when the plant is seen to be already wilting through a developing dryness at the root, then the recovery of turgidity may on occasion be anomalously delayed, or may even be postponed for ever. This all-too-familiar phenomenon gives visible indication of the contributary action of fertilizers in regard to drought-induced root damage or root death. It is of course mentioned in the literature of horticultural science. Readers wishing to know more about the behaviour of the roots of cacti and succulents during droughts may be referred to an article by our own David Green in our Branch Newsletter Vol. 6 (2000) No. 1, and to the treatise 'Environmental Biology of Agaves and Cacti' by P. S. Noble (1988).

The roots of most cacti and succulents are indeed specially adapted to withstand drought, and are to a greater or lesser extent more durable in this respect than are those of ordinary leafy plants. Nevertheless, the above-described phenomenon clearly indicates that the second safety criterion is more restrictive than the first, as indeed the ionic dehydration concept also suggests. Since No. 2 is already thought to be the maximal generally tolerable in regard to the first criterion, it thus appears that for most purposes No. 1 will be the best out of the three available numbered choices.

When I wrote Part 1 I suggested a No. 2 strength except for the soft succulents and epiphytic or saxicolous cacti. However, further trials carried out during the three succeeding growing seasons (1998-2000), together with consideration of various sporadic and random cases of root loss subsequently led me to drop No. 2 in favour of No. 1. I have now been using this weaker strength for all my general potting-on and repotting, and I have found that it gives a better recovery whenever the latter drastic operation is applied to items long neglected or for other reasons (e.g. compacted compost) in need of it. Indeed I find that in obviously debilitated cases a still weaker mix gives a higher survival rate and a more rapid recovery. In one or two cases, which had been slowly deteriorating for very many years (in spite of repotting) I transferred the remaining living bits to a mix of garden loam, peat, and coarse sand, but with no fertilizer then or subsequently. Eventually they re-rooted and then made good healthy growth! It remains to be seen how long this growth will continue. The plants involved included Aloe variegata, Haworthia cymbiformis and Epiphyllum phyllanthoides, and a few others whose identity I cannot now recall.

There are certain desirable plants which grow vigorously when correctly treated, but which are nevertheless to be reckoned as very delicate, in that any root damage usually leads to death of the complete vascular system, thereby eliminating all possibility of any subsequent re-rooting. Such plants include some of the Notocacti and the delightful but notorious Astrophytum asterias. Caution demands that these plants should be accomodated only in very weak composts.

Recommendations to use only weak composts should not be greeted with dismay, since for most cacti and succulents the plant's ability to both take up and use nutritional additives is limited, due to the smallness of the photosynthetic and respiratory areas. Some species are of course habitually hungry, and demonstrate their needs by extending their roots beyond the drainage holes, or by producing aerial roots in odd places. The temptation to cater to vigorous species by using a compost stronger than that proposed should, I think, be resisted. A theoretically preferable strategy would be to use a liquid feed, and to administer it only during periods of active growth. The point is that liquid feeding presents small and immediately available quantities in solution directly to the plant roots, whereas extra base fertilization incorporates large reserves into the microstructure of the loam and peat constituents of the compost, capable then of producing a permanent and therefore unwanted increase in the strength of the soil solution.

In view of the possibility of liquid feeding and the demonstrable benefits which it can bring it may reasonably be asked whether base fertilization is needed at all, although I myself find the theoretical arguments in its favour to be pretty convincing (see Part 1). However, the aim of the present article is not to answer that question, desirable though an answer might be. The aim is to determine base fertilization levels that are low enough to be safe under xerophytic conditions.

5. The Choice of Base Fertilizer

The slow-release attributes of purpose-designed base fertilizers soften significantly the shock of transfer to a stronger compost, and for this reason it should be considered mandatory always to use such fertilizers when preparing one's own mixes, and not to substitute them by a nutritionally equivalent amount of solubles. The need for calcium must also be remembered. In ordinary horticulture calcium carbonate in the form of powdered limestone or powdered chalk is used for this purpose, but in xerophytic cultivation these materials lead to an undesirable rise in the pH. They should therefore be substituted by powdered horticultural grade gypsum (which does not affect the pH). An equal weight will prove satisfactory. I do not yet know whether gypsum is bad for ‘lime haters’, but I don't see any reason why it should be.

When a base fertilizer is added to a compost the resultant strength (i.e. the equilibrium concentration of the nutrients in the soil solution) is conditioned inversely by the amounts of loam, baked clay, vermiculite, charcoal, peat, coir and humus that are present, but not to any significant extent by any sand, grit, gravel or perlite that may also be there. The reason for this is that these latter materials make only a very small contribution to the total amount of microsurface area on which the nutrient molecules or ions can lodge.
It follows that the addition of extra amounts of these various chemically inert drainage materials should not be accompanied by extra amounts of base fertilizer. It follows also that a growing medium made entirely from sand, grit, gravel and perlite cannot be base fertilized at all.

6. Some Unfortunate Contemporary Mistakes and Omissions

The second safety criterion has yet to find its way into the general consciousness. Growers of cacti and succulents have of course long been aware that there is some correlation of a statistical kind to be found between drought and severe root damage or root death, and in response to this some recommend a spray-administered reveille, while others even suggest that the resting season should never be completely dry. However, nowhere in all my perusals of the cactus and succulent literature have I found recognition that the strength of the compost is the operative factor in the correlation. Yet the proposition that compost strength is the key to the matter could quite expeditiously be put to formal trial, demanding merely the imposition of a drought following some relatively short period of successful moist cultivations at various suitably chosen compost strengths (with of course verification of root health and active root growth prior to the drought's onset).
Some of the more recent English-language cactus books which I have inspected suggest the use of JI composts yet do not venture to give any advice in regard to the strength or strengths to be selected. This I find rather sad, especially where the books concerned are written for beginners.

Those which I have seen and which do make specifications on the matter recommend the higher strengths, usually No. 2 but for some plants even No. 3. At the same time they also recommend a long waterless resting season, yet contain no warnings about the various deleterious effects that may from time to time ensue. This I find puzzling. Could it be that summer droughts are more dangerous than winter droughts, and that root losses which I have attributed to the winter actually arose earlier? Or could it be that some other unsuspected environmental factor is at work? Or could it be that in these advices we are dealing not with consistently organized factual systems, but only with mutually incompatible items of hearsay? I wish I knew. The books which I have in mind here, and which I have with me as I write, are 'The Encyclopedia of Cacti' by Cullmann, Götz and Gröner (1986), 'How to care for your Cacti' by Pilbeam (1984), and 'How to care for your Succulents' by Pilbeam (1984). The last-mentioned recommends No. 2 even for small Crassulaceae of various sorts, for Dudleyas, for various mimicry Mesembs, and for various Stapeliae. In my experience this contravenes already even the first safety criterion (Section 3), and a fortiori therefore also the second.

If however we go back to an earlier generation we find universally the commendation that JI No. 1 is suited to the needs of almost all of our cacti and succulents. I have to hand here 'Cacti and Succulents' by A. J. Huxley (1960), 'Cacti and other Succulents' by R. Ginns (1963), and 'The Marshall Cavendish Encyclopedia of Gardening' edited by Peter (not David!) Hunt, and published in weekly parts in 1968 - 9. Doubtless there are other works from those days and carrying the same message – a message different from that which applied to pot plants then and continues to apply to pot plants now! Why then has the message for cacti and succulents departed from that which was earlier established?

For my awareness of the last-mentioned comprehensive and sumptuously produced compilation I remain permanently thankful to a certain Mrs. Patience Taylor, a very dear artistically sensitive lady now long departed, who around the time of publication was for a while an attending member of our Branch. She invited my late wife and myself to see her plants and her parrot and her tortoise and her photographs and her paintings and various other odds and bits and her amiable husband and their small but welcoming home in Chantrey Street (which ran parallel and next to Edge Lane and just to the east of the church which still stands on Durning Road. She showed us the first few issues and most generously presented them to us, and we were so impressed by them that we subscribed to all the rest ourselves. Besides the unprecedentedly rich (for such a wide-ranging publication) photographic and textual coverage of cacti and succulents there is a remarkably extensive and well thought out section on their cultivation, self-evidently composed by some person with considerable hands-on experience. I can find no precise indication as to who this particular writer actually was. A list of contributors to the work overall is however to be found, on p. 2352, and in it can be discerned the names of at least seven of the then recognized cactus and succulent experts. Extremely germane therefore to our present discussions must be the various recommendations on composts, which in regard to JI amount to No. 1 plus coarse sand for almost all cacti and succulents and almost all of the numerous genera specifically mentioned and treated individually. Frequent repotting (from twice a year to once every three years) also forms part of the general programme advocated but, not too surprisingly in view of the publication date, there is no mention of the still new-fangled soluble feeds. Weak feeds (presumably with liquid manure or with one of the synthetic high-nitrogen growth stimulants available at that time, such as Sangral or Liquinure) are suggested for certain large-flowered epiphytic cacti (including Aporocactus), but are otherwise mentioned only by way of warning against them, on account of the lushness which they produce. Even so, and notwithstanding this nutritional limitation, no recommendations for the use of JI No. 2 are to be found, save in connection with some of the large-flowered epiphytic cacti, and none whatsoever for the use of JI No. 3.

7. The Treatment of Purchased Plants

Some amateurs and almost all professionals take great pride in offering for sale only plants which have grown in and are established in their pots or, in the case of mall order, plants whose roots may be seen directly to be alive. My evaluation in the former case is that a disturbance of the root would be cultivationally and ergonomically undesirable, and so I do not repot upon purchase. Rather, I allow growth to continue without check and, having in mind a possible violation of the second safety criterion, I introduce water only by gradual stages the following Spring (a precaution which, as I have implied in Section 3, is alien to the true nature of a cactus, and unnecessary if the compost is suitably weak).

However, we do not inhabit an ideal world, and quite frequently one may also encounter seedlings or small rooted cuttings, often of interesting species, but giving every impression of having been potted up only a few days prior to sale (a mismatch in size – large pot and small plant – may already arouse some suspicion!). The purchase of such items can be rather a gamble, since at the time one has no indication either of the health of the root or of the suitability of the compost. During the period subsequent to my writing of part 1 I have had a significant number of unfortunate yet highly informative JI - linked experiences in this respect, which for me is a new phenomenon. I have thus come to believe that many amateurs nowadays are even more optimistic (or less well informed!) regarding the fulfilment of the first safety criterion than I sometimes was, in the days before I started the present long series of investigations. This is somewhat surprising to me, because it is after all a well established principle within general horticultural doctrine, that small seedlings and small rooted cuttings need strengths in the range No. 0 (i.e. Seed) up to No. 1, but not higher. There are no grounds for any general exemption of cacti and succulents from this provision, and it is perilous to assume otherwise!

Having had several such small and recently potted plants gradually dry up and die (in spite of partial shading and adequate watering!) I subsequently sought out two of the vendors, and thereupon learned that both of them had used JI No. 3, and that one of them had thrown in some extra fertilizer "just to be sure".

In view of all this I now consider it highly advisable, in all dubious cases, to mistrust whatever compost has been used, and to repot straight away into a compost of strength No.1 if the plant seems to be reasonably robust and tough, and otherwise something weaker. This usually works, provided that the transfer is done before the original compost has had time to dry out.

The problem is not confined only to small propagations. I have encountered it also with larger plants, and altogether with at least seven different amateur suppliers. The most common symptom consists in a lack of turgidity and a lack of growth, but in the more severe cases there may be other manifestations. These need not be described here, since I have already compiled a listing of them in Section 2 of Part 2.

The associated inhibition of normal growth inevitably reduces the life prospects of any affected plant. Therefore, even if there is nothing amiss to be seen, other than a seeming slow decline, one should still act straight away. The best action is to repot at once into a suitably weak or a zero-strength compost (depending on the state of the plant). The alternative, to apply repeated flushings at hourly intervals, is hardly likely to commend itself to cactus growers. The worst strategy is to do nothing other than hope and pray!

8. Apologia and Appeal

Nature provides us with a great jumble of unsystematized observations. Popular horticultural literature presents us with a mass of baldly stated rules of procedure. Scientific advances support the belief that an underlying logical and reliably predictive structure may be found. Both experience and logic teach us that baldly stated rules, no matter how cleverly devised, are always incomplete and open to misinterpretation, and are never predictive.

The writing of the present paper has severely taxed my abilities, but effort brings its own reward, which in this instance comprises an increase in understanding much more than what I expected to accrue when I started. I hope that it will also bring rewards to others. That, however, will depend upon whether anybody is sufficiently interested to read it!

Would it be too optimistic of me to express the hope that some readers with experiences of JI composts and/or base fertilizing might report their findings in the Newsletter? Our Editor eagerly awaits contributions. Even the most elementary observations – what plant, what compost, what level of fertilization, what outcome – could help to build up a more generally reliable overall picture.

9. Acknowledgements

Throughout my long-protracted and still far from complete investigations an ongoing correspondence with Roy Mottram of Whitestone Nurseries has been very helpful to me, and his continuing interest most encouraging. Both are acknowledged with gratitude.