Article 83 – ‘Plant husbandry 1’

Hi, welcome to Taiga Bonzai, we receive many questions on ‘Plant husbandry’ for example, ” If we plant a seed it will probably germinate, but it would be good to know a little more science on the subject for better understanding.” Okay, we will discuss these issues in the next 4 articles, but as extensive research has already been written (and we will point out the appropriate articles) the discussions will be in brief.

Introduction – germination is defined into two categories Epigeal (above ground) and Hypogeal (below ground) as a seed germinates the first structure to emerge from most seeds is a root from the embryonic called a radicle, this primary root is referred to as a taproot. Smaller lateral roots (secondary roots) arise from the taproot which in turn produce even smaller lateral roots (tertiary roots) these serve to increase the surface area for water and mineral absorption.

Epigeal germination
Hypogeal germination

The above images show the stages of germination from the radicle to the first true set of leaves and needles respectfully. Cotyledons are the first leaves produced by plants, but they are not considered true leaves and are sometimes referred to as ‘seed leaves’, because they are actually part of the seed or embryo of the plant. These seed leaves serve to access the stored nutrients in the seed feeding it until the true leaves develop and begin photosynthesizing.

Root growth – roots grow in length from their ends only, the very tip of the root is covered by a thimble-shaped root cap called the calyptra, which protects the growing tip as it makes its way through the soil. Behind the root cap lies the apical meristem here cells are produced, some are added to the root cap, but the majority are added to the region of elongation, which lies just above the meristematic region. Above this lies the region of maturation where the primary tissues of the root mature, completing the process of cell differentiation that actually begins in the upper portion of the meristematic region. (shown below)

Aerial roots – some roots called adventitious roots arise from an organ other than the root, for example from a stem or leaf. These adventitious roots often referred to as aerial roots can hang long distances before coming into contact with the soil or remain dangling in the air. Some of these including the Screw pine and banyan do assist in supporting the plant in the soil, aerial roots are the primary means of attachment to non-soil surfaces such as buildings, rocks and other plants for example. The Ficus watkinsiana family Moraceae (strangler fig) named for their pattern of growth upon host trees, which often results in the host’s death.

Image courtesy of By Poyt448 Peter Woodard
Ficus watkinsiana on Syzygium hemilampra, Australia

A number of other specialized roots exist among vascular plants for example. Pneumatophores an aerial root specialising in gaseous exchange are commonly found in mangrove species that grow in saline mud flats. These are lateral roots that grow upward out of the mud and water to function as the site of oxygen intake for the submerged primary root system.

Other root systems – the roots of certain parasitic plants are highly modified into haustoria, a rootlike structure that grows into or around another structure to absorb water or nutrients, mistletoe and members of the broomrape family are good examples of this. Many plant roots also form intricate associations with mycorrhizal soil fungi, a number of non-photosynthetic mycoheterotrophic plants including the Indian pipe rely exclusively on these fungi for nutrition.

Root functionality – the primary tissues of the root are from outermost to innermost, the epidermis, cortex and vascular cylinder, the epidermis is composed of thin-walled cells and is normally only one cell layer in thickness. The absorption of water and dissolved minerals occurs through the epidermis, a process enhanced in most land plants via the presence of root hairs – slender tubular extensions of the epidermal cell wall that are found only in the region of maturation.

The absorption of water is achieved via osmosis, which occurs because (a) water is present in higher concentrations in the soil than within the epidermal cells, where salts, sugars and other dissolved organic products are contained. (b) The membrane of the epidermal cells is permeable to water but not to many of the substances dissolved in the internal fluid. These conditions create an osmotic gradient, whereby water flows into the epidermal cells, this flow exerts a force called root pressure, that helps drive the water through the roots.

The cortex conducts water and dissolved minerals across the root from the epidermis to the vascular cylinder, then transported to the rest of the plant. The cortex also stores food transported downward from the leaves through the vascular tissues, the innermost layer of the cortex consists of a tightly packed layer of cells called the endodermis, which regulates the flow of materials between the cortex and the vascular tissues.

Why no tap root? – In bonsai many practitioners remove the ‘tap root’, but the ‘tap root’ enables stability and water absorption so why remove it? The following deciduous species have rather large tap roots Oak Quercus, Black Walnut Juglans nigra, Silver Fir Abies alba and White Mulberry Morus alba. Coniferous species contrary to popular belief do not have long tap roots, their lateral roots and tertiary roots spread outward and grow downward which gives stability however, there are some exceptions including the Long Leaf pine Pinus palustris that have large tap roots.

In order for these and many other species of tree to become bonsai the roots have to be pruned and the more vigorous the root growth the more pruning is required. In Japan and China young trees are planted in deep pots to encourage root growth and after a few seasons they have their tap roots removed to allow the lateral and tertiary roots to develop and thicken; these roots if near the base of the trunk are the potential nebari.

Root damage – many plants will survive and recover from root damage providing the damage does not exceed 1/4 of the total root zone. Most of the important feeder roots of trees or shrubs are within the upper six inches of the soil and if damaged, uptake of water and nutrients is restricted reducing growth. In addition, root damage may take months or even years to progress, and it is during this period where problems begin which can cause symptoms of decline or death depending on the situation and how much damage occurred.

One of the biggest problems when root pruning bonsai is the lack of care taken, we have witnessed countless instances where the root ball is attacked with 2, 3, and 4 pronged instruments. The roots are basically ripped apart causing irreparable damage and as stated if more than 1/4 of the total root ball is damaged chances are that the tree’s health will diminish for some considerable time and this is where it is susceptible to attack from pests and disease.

Root pruning is an important factor in bonsai horticulture and should not be attempted half heartedly. At T.B. we have some large bonsai (Omani dai class) and these do take considerable time to re-pot. When teasing out the root ball a blunt single root hook is used that does not cause any damage. After which the roots hanging down and separated can be pruned accordingly with sharp shears nonetheless, others will use instruments that they prefer.

This brief discussion on germination and in particular the functionality of a plant’s root system may lead to a better understanding of its importance, more on root pruning can be found in articles 08 ‘Styling, wiring and pruning’ and 54 ‘Summer pruning’. Until next time, BW, Nik.

Article 82 – ‘Organic versus chemical’

Hi, welcome to Taiga Bonzai in this article we discuss the never ending problem of pest control that occurs on an annual basis that if not kept in check, will increase to unprecedented levels. In eradicating the unwanted two schools of thought are given, the ‘organic or chemical’ approach.

Introduction – there are countless species insects of which 10 million exist throughout the globe however, some entomologists say the number could be higher. Not all are a major problem, in fact many are predators helping to eradicate those whom cause devastation to plant life, these include Ladybugs Coccinellidae, Green Lacewings Chrysopidae, Honey Bees genus Apis, Praying Mantis family Mantidae, Spiders family Arachnida, Ground Beetles family Carabidae, Soldier Beetles family Cantharidae, Assassin Bugs family Reduviidae and Robber Flies Asilidae.

Eradicating the unwanted – arguably it is the most common of pests that are the problem, but much depends in what part of the world one resides as there will pest species endemic to your region. Here in the northern hemisphere pests include: Red spider mite Tetranychus urticae, Mealybugs Pseudococcidae, Aphid Aphidoidea, Scale Coccoidea and Sawfly Craesus septentrionalis all of which destroy plant tissue causing major problems and even death. Of course there are many other species to contend with some of which are immune to control, recent published articles ‘unseen enemies’ parts 1 to 4 gives more in depth information on this subject.

Finding a solution – according to the National Pesticide Information Centre (NPIC) there are different methods to eradicate pests and disease, “Fungicides are pesticides that kill or prevent the growth of fungi and their spores. They can be used to control fungi that damage plants, including rusts, mildews and blights.” “Fungicides work in a variety of ways, but most of them damage fungal cell membranes or interfere with energy production within fungal cells.”

Chemical approach– insecticides for eradicating pests are normally purchased in liquid form used in various spraying apparatus, they are poisons and can be classified in several ways on the basis of their chemistry, their toxicological action, or their mode of penetration. These chemicals not only kill the intended victims, but also other non-insect pests that are beneficial. The 4 categories are; Organic insecticides – Synthetic insecticides – Inorganic insecticides – Miscellaneous compounds.

The chemical Malathion

Banning the poisons – these chemicals regardless of category are detrimental to other plant life, to animals and human health. For example, Malathion manufactured by Dow Chemical is linked to developmental disorders in children and has been found by the World Health Organization (WHO) to be probably carcinogenic to humans. Conservation and public health groups sued the Trump administration and Environmental Protection Agency (EPA) chief Scott Pruitt, for failing to protect endangered wildlife and the environment from the dangerous pesticide.

Thus far the total ban on insecticides is 12 world-wide with another 27 under investigation, according to Nathan Donley in his ‘Environmental Health’ volume 18 Article number: 44 (2019) “The USA lags behind other nations in banning Paraquat, one of the most acutely lethal pesticides still in use today.” Not a ‘gold medal’ winning performance by any standard – so what is the problem, why are nations so indecisive in taking action against chemical usage?

Arguably it is attributed to 4 criteria. (a) Not all insecticides are effective because much depends on the species and many we know of are immune. (b) Nations are concerned with their own pest problems and will avoid using chemicals that have not been tried and tested. (c) Import/export using insecticides on crops is dangerous to human health, hence people are reluctant to purchase food if they are unsure of its origin. (d) The financial aspect – according to the GlobaL Insecticide Market it was valued at USD 12.11 million in 2020 and is projected to increase to USD 17.70 million by 2026. This market has high employment numbers that will be jeopardised if profits are diminished.

Organic approach – a solution called insecticidal soap which has been in use for eons is believed to cause damage to an insect’s cellular structure, the soap is sprayed on to an infected crop and the pest is coated and eradicated forthwith. It is contended that the effectiveness of insecticidal soap involve a physical effect on the insect for example. Damaged membranes, dissolving the insect’s wax coating leading to death by dehydration, disruption of the insect’s hormones, interference with the insect’s ability to breath and negative effect on the insect’s metabolism.

Horticultural soap

Insecticidal soaps are made from potassium salts of fatty acids (potassium laurate) which have a devastating effect on the insects, but not the plants on which the insects are devouring. Insecticidal soaps are most effective on soft-bodied insects including aphids, greenfly, whitefly, blackfly, mealybugs and scale insects. They can be effective against larger insects such as sawfly and other caterpillars. Predator insects such as ladybugs, honey bees, praying mantis, beetles, assassin bugs and wasps are not usually affected by insecticidal soaps and this makes them useful especially in confined spaces, greenhouses and polytunnels where said insects are welcomed.

Nonetheless, some plant species are adversely affected by spraying insecticidal soap, hence it is prudent to do a test before attempting a full-scale application. Insecticidal soap is permitted under most organic regimes, it is safe where children, birds and domestic animals are concerned. Insecticidal soap is a relatively simple product that works on contact and acts on the physiology of insects to eradicate them. Insecticidal soaps have several advantages over pesticides, they are non-toxic, leave no unwanted residue and are less expensive than chemical insecticide solutions. Insecticidal soaps can be purchased from appropriate outlets or made at home, here is a simple recipe example.

Step 1. – fill a 1 gallon (3.785 L) container with either rain water or distilled, not tap water as it contains alkaline properties making it hard thus reducing the effectiveness, make sure to leave room a gap at the neck of the container for other ingredients.

Step 2. – add 2-½ tablespoons of mild unscented liquid soap and 2-½ tablespoons of oil either vegetable, peanut, coconut or olive it matters not which. Both the liquid soap and the oil act as surfactants to prevent the solution from quickly running off the plant’s leaves when sprayed. The longer the solution remains on the plant’s foliage, the better the chance of dispatching the insects. Do not increase the ratio of soap or oil, it must be a very mild solution in order to protect the plants.

Step 3. – replace the container cap or lid and shake the solution to disperse the ingredients evenly, then pour the required amount into a spray bottle shake again then begin spraying the infected plant. It is advisable to re-shake the container prior to re-filling the spray bottle as this remixes the solution. The above horticultural soap recipe is one approach, there are many others using additional ingredients including vinegar for example, hence it might be prudent to research the subject further for piece of mind.

Although insecticidal soaps are safe for many plants, vegetables and fruit trees, a few are sensitive to the solution resulting in leaf damage, these include sweet pea, begonia, impatiens, azalea and rhododendron. If unsure whether it is safe to use insecticidal soap err on the side of caution and do a sensitivity test first on 2 to 3 leaves of the plant. If there are no ill effects after 24 hours and treated leaves look as healthy as before then it is safe to continue spraying, if the results are the opposite do not treat the plant further.

The fight continues – we wrote this article in September 2021 with the intention of posting it, but it was withheld due to Covid 19 and the restrictions imposed, although certain mandatory commitments still required our attention. In addition, there were reports of bans on various products including food and increases in different government’s legislation further exacerbating the problems at the time.

As scientific researchers we wanted to find out the reason behind this phenomenon, hence we wrote a series of articles called ‘unseen enemies’ 62 to 66 that gave rise to a lengthy discussion on how pest and disease was spreading throughout the globe. A huge problem caused by mankind’s idiosyncratic actions over the eons. Pests and disease that were once endemic to particular regions have spread world-wide destroying forestry and horticulture on an unprecedented scale. This article ‘organic versus chemical’ is a way of dealing with common pest and disease problems that we know of, but it is not an effective solution on all invading species. Until next time, BW, Nik.