There are strange plants in the world; have you ever heard of Laburno-cytisus adamsii? This is a rare and not very beautiful thing that was accidentally created in 1825 in the nursery of a Monsieur Adam near Paris. They were grafting (probably shield budding) a choice variety of Cytisus purpureus onto Laburnum anagyroides rootstocks when one of them went wrong.
A cytisus bud was penetrated by a laburnum bud pushing up from under and through it creating a mixed plant or chimera of both. The laburnum formed the core and over this was overlaid the cytisus. Both existed in both unsullied and mixed forms throughout the small tree that formed from this chance fusion. It produced yellow flowers of laburnum on some limbs, purple flowers of the broom on others, with mixed coppery coloured flowers on the rest of the branches.
This not very lovely plant has been propagated ever since and can still be found commercially simply because of it's almost unique peculiarity, it is one of the very few known graft hybrids. The fact it exists at all helps give some credence to one of the oddities described by the ancient horticultural writer Columella. He lived just after the time of Christ and was appointed by the Emperor Claudius to accumulate all the horticultural knowledge of the times into one book. This is not available in English but Latin/English copies can be found of the Harvard University Press's edition. Columella's a fascinating work full of interest to the gardener but a couple of things he suggests are very odd and without knowing of the chimera above you would dismiss them out of hand, and probably then give him less credit elsewhere.
Columella claimed that grapevines existed that produced bunches of grapes of more than one variety, and not just two or more separate branches worked on the same roots. He said these strange hybrids were made by taking several similar sized cuttings of different varieties, rooting and growing them on all crammed together in the middle of a piece of horn or earthenware pipe. In a few years once they had all grown big and the mass had fused in the pipe he said break the pipe up and cut across the fused stems. Then cover the cut end by three inches of fine soil and the vine(s) that emerge(s) would be of a mixed sort with different berries in the same bunch.
Well he may have been lucky; I would've thought it likely a bud would usually have broken from the roots first. However 'Family' trees are not a new invention, and in Paris markets of the Victorian period they regularly sold speciality multi-flowering shrubs where three or more cuttings of different sorts were rooted while all were bound together in a pipe. So if multiple variety family vines were being produced by this method in Roman times it may be that when one of these piped vines died of constriction, as they inevitably must, it popped up a bud hybrid. His assertion that it can be recreated at will I find dubious, it did not work on my sole attempt, but I believe it quite possible if enough attempts are tried.
Less likely true was his claim that if you took a cutting and removed all the pith then it would grow into a vine that bore seedless grapes, mine didn't but why don't you try? He, like many of his contemporaries, also claimed you could graft almost anything onto almost anything else by inarching -fusing the two plants together by a graft while each still retains it's own roots. I'm told this cannot work, yet again maybe if enough attempts are made... And although it is unclear from his text I suspect he may be achieving success by building up interworked grafts of mutually compatible plants to bridge the two incompatible ones. After all extra work was no barrier; they had slaves. Indeed the Romans dug their soil six feet deep, or rather their slaves did.
But going back to strange grafts; I came across an old book that said if you carefully cut the eyes out of one sort of potato and buded them into the eyes of another, say of a different colour, you could get a crop of potatoes that were a mixture of both. It claimed to work the same trick by taking a small rooted shoot of each sort, cutting them in half vertically and joining the two halves together to produce a pair of mixed plants. I've tried but couldn't make either of these work, but I'm not very good at such small intricate grafts.
Even more crazy yet assuredly true is that if you take a potato and chit it rubbing off the first and second crop of sprouts that emerge from the eyes, or if you remove the eyes entirely, you will eventually get sprouts form from vestigial buds under the skin; which may be of a different sort to the tuber you started with. For example if you do this with Golden Wonder, a russet, you will, if the tuber has enough vigour, in the third or fourth set of sprouts start to get Langworthy, an old and near extinct variety that is not russetted and from which Golden Wonder was a sport. This is so weird that a supposed expert rubbished my reference to this until he was shown the original paper!
And this is often the trouble, experts may be expert but narrowly so, especially in a commercial world. For example I was showing a well known professional gardener and nurseryman around my propagating area and he was surprised to see me rooting Poncirus and Citrus cuttings as he did not consider it possible. In fact it is not practical, i.e. most of them die; which is no use to any commercial gardener, however to the amateur then such odd success is quite sufficient. (Meyer's lemon is the easiest to root though it then does not have the same vigour as when grafted on a good rootstock.) Likewise on a national radio programme many years ago we foolishly stated that it was impossible to root the Maidenhair tree, Ginkgo biloba. Well it's an ancient coniferous like plant being itself a monotypic genus and it doesn't have a structure that should ever allow it to root, theoretically. However several listeners who didn't know they couldn't possibly have succeeded in rooting cuttings of it wrote in claiming they had done so!
In nature there is always going to be an exception. So although most gardeners would agree that an avocado or a grapefruit tree cannot be hardy enough to survive outdoors in England surprisingly some do! But certainly not enough to make them useful as garden plants, and never as a crop! Thus the general advice we are offered is not incorrect, it just has exceptions that can only be discovered by experiment.
Almost all our information is equally incomplete, filtered and biased, especially by commerce. For example; we get recommended to grow all male asparagus. Why? Well because it gives the highest yields per acre. The spears are not small, but they are small by comparison with what the equivalent female plants produce. But females produce less crop per acre and they waste energy on seeds which cause a 'weed' problem commercially so are not considered. However seeding is hardly a big issue in the garden and the females do throw much bigger spears, and as a gourmet gardener I'd rather have slightly fewer enormous spears than more smaller ones.
Likewise the accepted treatment of potatoes comes from commercial practice where yields per acre are high (we won't talk about eating quality here!) and almost all the costs are the labour. Thus the methods advocated are not necessarily the best for gourmets and kitchen gardeners. For example, as I wrote in an article on potatoes in last year's April Kitchen Garden magazine, the commercial experts tell us not to bother chitting our potato sets 'rose end up' as they just chit them thrown higgledy piggledy in trays. But I'd read the old boys did not save small sets as we do but saved big ones which they cut in three; using the rose end and the middle slice and discarding the haulm end. The reason they gave for this was that the haulm end sprouts came late and gave poor crops, thus their other recommendation to chit the rose end up.
Well I tried the experiment and chitted half some sets rose end up and half down, and planted them the same likewise. The rose end up sets gave better plants that lived longer and gave half as much crop again as the wrong way up ones. It hardly seems credible such a benefit should exist and not be attempted in commercial practice, but try it for yourself and see. Likewise commercial growers disparage the advice to remove the flowers and tomato like seedpods that form on some varieties as "not worth the labour". Well it may not be worth it for them but an old experiment I came across showed an increase in yield of a ton per acre for simply removing the flower heads.
And as to how deep to bury the sets! The arguments I have read both for deep and for shallow burial, unbelievable. The tubers must be covered to prevent them greening and to prevent their infection by blight spores. Earthing up the haulm does, in long season varieties, cause more side shoots and tubers to form BUT others claim that shallow planting also makes it easier for more tubers to form. Certainly the depth recommended for planting seems more to do with the ease of cultivation and the extraction of the crop mechanically than with the actual maximisation of yield. As I've written before I did an experiment growing King Edward's, an old variety well known for preferring deeper planting and I put the sets in at a few inches, six inches, a foot, a foot and a half and two foot deep. The deepest planted were not much later to emerge, were the healthiest and darkest plants staying lush longer in a dry summer and gave the biggest crop. Mind you it was an absolute b****** to dig up!!!
Another really old controversy is whether or not early dug seed potatoes crop earlier the next year than later dug ones. This may seem simple to prove but the number of letters in old magazines prove that it is hard to decide either way as half find one way and are as defensive as the others who found the contrary. My experiments were as inconclusive as some plants did and some did not do better. It was exactly the same when I tried a large scale astrological experiment; the only fair conclusion was that it was better to sow everything in at least a couple of batches a few days apart. Beyond that was mayhem; some profoundly proved one day better for something while equal numbers of others showed the opposite.
Indeed the only real conclusion in gardening is that there are no rules only guidelines. Some people can root a dried up stick and others can't start a bean seed. Some methods and varieties work for you and others fail; the only way for you to find out is to try them out for yourself.