Gardening, Grow Your Own, How To, Jorge, Planting, Plants

Growing your own goji berries is an excellent way to reduce your carbon footprint, save money and provide a source of nutrients for your family. High in vitamin C, B2, A, iron, selenium and the antioxidant polysaccharides, they constitute a welcome addition to a balanced diet and are great as part of a smoothie, or served with oats. Growing goji berries is relatively easy as it is well adapted to the UK’s climate as with other himalayan species.

Growing goji berries from seed is not recommended as seeds are prone to rot and seedlings require warm conditions for 12 months, which is both impractical and costly. Hence, we recommend two year old plants that are winter hardy and ready to fruit. It you do wish to grow from seed, rot can be prevented through an irrigation system ensuring moist soil. Goji berries work well in containers and normal advice applies.  

Soil and Sun Requirements

Goji berries are from the solanaceae family and possess a similar nutrient requirements to tomatoes. Hence, as nitrogen hungry plants we recommend applying fertiliser at the start of the growing season. However, as they are sensitive to salinity, we recommend avoiding inorganic fertiliser, which contains soluble salts. Compost also contains salts, so should be a small proportion of the potting mix (20%). Goji berries require full sun, but also benefit from shelter. They work well as hedges and possess delicate white and purple flowers, so function well as an ornamental.


Mature plants can reach 3m high and 1.5m wide. Hence, we recommend they be spread at 1m apart. As with all potted plants, it is important to keep the soil ball intact and ensure it is planted at the same depth as it is in the container. (Using a spirit level or ruler can help you keep it is level.) This will ensure the roots are within range of the nutrient rich top soils, but not exposed as to lead to air pruning. We recommend you dig a hole bigger than the circumference of the container and fill it with a mix of fertiliser, compost and garden soil, which is superior in structure and nutrients to garden soil. Be sure not to pack the soil too tight or compress the soil as this will reduce retard root growth. Once this is complete be sure to water thoroughly.

Next, you are to remove all nearby plant life and mulch. By doing this you are reducing competition, allowing the growth of a healthy root system, and improving the soil’s structure, which gives the plant access to air and water. Mulch should not come into contact with the shrub’s main stem as to ensure it does not come diseased, and be level with a depth of 2 and 3-4 inches for fine and coarse materials respectively. Mulch can be replenished annually, depending on the material, and the area it covers should be increased as the shrub’s roots expand.


The most important function of pruning is to remove old, dead and damaged stems to make room for new stems. (Flowers and berries are borne on stems grown in the spring and autumn of the year before.) By pruning stems you encourage the production of more laterals, leading to higher yields. Pruning has the additional advantage of increasing sunlight penetration and improving foliage drying, which is especially important with goji plants susceptible to verticillium wilt. Hence, it is also important to water at the base of the plant. We recommend watering thoroughly, every so often, rather than little and often, as this will encourage the formation of deep roots, which helps the plant endure dry periods. Pruning should take place in the spring, just as the plant starts to grow.


Goji berries produce the biggest yields in their fourth year, while at two you can expect a kilo of fruit. To harvest, wait till the fruit is deep red and fully ripe (usually midsummer), and then shake them onto a blanket. Handling can make them turn black. To dry goji berries, leave them on a sheet of baking paper in a cool, dry spot out of direct sunlight.

If you are interested in growing your own goji berries, Primrose offers two year old goji berry plants from just £4.99.

Jorge at PrimroseJorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!

His ideal afternoon would involve a long walk, before settling down for scones.

Jorge is a journeyman gardener with experience in growing crops.

See all of Jorge’s posts.

Composting, How To, Jorge, Planters, Planting

The amount of compost needed for a planter depends both on planter size, its material and the plant you wish to grow. Compost is important as it will improve your soil’s structure, increasing its available water capacity (AWC), which is especially important for planters. Calculating a planter’s volume (measure in litres) is relatively easy, but it is first important to work out the compost/garden soil ratio required for a particular plant.

Compost/Garden Soil Ratio

Now why do I want to mix compost with garden soil? Firstly, garden soil is incredibly complex with numerous soil organisms that help boost your plant’s health. These organisms will help improve the structure of your soil and break down organic matter into mineral nutrients, available for uptake by plants. However, there is the possibility of inducing pests and diseases, so we recommend avoiding soils that you have previously planted. Secondly, garden soil will help improve drainage, ensuring your planter does not become waterlogged. Lastly, using garden soil will save you money and lower your environmental footprint.

While compost does add nutrients to the potting mix, its major advantage is improving the water-holding capacity of the soil, which occurs through two mechanisms. Firstly, compost contains carbon, as well as other nutrients, that provide food for soil organisms. These organisms function to increase a soil’s porosity – the percentage of soil that is pore space or voids. Secondly, compost improves soil structure by gluing tiny particles of rock (sand, silt, or clay) together into peds (aggregates), which is the basis of all good soils. These peds have adequate pores to allow entry of air and water, both which are essential to plant health. The increased porosity has its origin in the fact compost is significantly lighter than conventional soils.

An ideal soil has a porosity of about 50%, equally divided between micro and macropores, which provides a good mix of drainage and retention. When it rains both macro and micropores become filled with water. Larger pores are the first to drain with light sandy soils taking about a day and heavy clay soils about three. Micropores remain filled and are unaffected by gravitational flow, the water held by electrostatic attraction. The smaller the pore, the more tightly the water is held. Macropores drain too quickly to be of much use to plants, providing little water, but allowing flows of oxygen to plants’ roots. Micropores retain water, available for use by plants. Hence, macro and micropores complement each other, allowing air and water to reach plants’ roots.

Picture credit: MesserWoland licensed under CC BY-SA 3.0.

Fascinatingly, small pores act to draw groundwater up through the soil, providing a source of water in the absence of rain. This phenomenon occurs due to the forces of cohesion (propensity of water molecules to stay together) and adhesion (propensity of water molecules to stick to other surfaces). When the force of adhesion is greater than that of cohesion the water rises, with the water near the edge of pore curving upwards. Capillary action can be easily demonstrated by dipping a paper towel in water and watching water climb the towel.

Soil textures – clay, sand, silt and loam – each have different drainage profiles, originating from the size of the particles. Clay particles are the smallest, sand the largest and silt in between. The larger the average particle, the faster the soil drains. Loam is comprised of about 40% sand, 40% silt and 20% clay and is considered the best texture, having the optimal balance of micro and macropores. Clay lacks larger pores, providing poor aeration and drainage, and possesses minute micropores too small for plants to utilise, reducing the soil’s available water capacity. Sand, on the other hand, drains too quickly, predominantly composed of large pores.

Compost increases the number of micro and macropores in the soil, greatly improving a soil’s available water capacity, and should be added to all soil textures including loam. B. D. Hudson’s 1994 paper demonstrated that for every texture as organic matter was increased by 1-3%, the available water capacity doubled. A 2000 study by A. Maynard found that the amount of water in a plow layer (8 inches) increased from 1.3 to 1.9 inches in soil amended with compost, providing a two week supply of water for vegetables, significantly reducing water stress.

An increase in the available water capacity is especially beneficial for potted plants that receive significantly less rainfall due to their container’s small surface area. We recommend the potting mix contain 20-50% compost with higher blends if your soil is clay, your plant thirsty, or the planter’s material porous as with terracotta. Compost will not provide all the nutrients needed, so we recommend the application of organic fertiliser. Mulching is also useful and will help improve water retention and soil structure.

Calculating Volume

A 1 litre cube. Picture credit: H McKenna licensed under CC BY-SA 2.5.

Volume is the sum of 3 measurements (length, width and depth) multiplied together and is expressed in cubic units (cm³, m³). Cubic units correspond directly to litres with 1 litre equal to 1000cm³.

Most planter retailers will give you the dimensions of a planter in cms that can be used to calculate volume. In not, you can use a tape measure. Compost is sold either in litres (l) or cubic meters (m³).

Note: most planter dimensions provided online will be the outer rather than inner dimensions, so you’ll need less compost, depending on the thickness of its sides.

Note 2: planters come in a huge range of shapes. Hypothetically you can calculate the volume of any shape (done by dividing shapes into smaller ones), but we recommend you simply approximate the shape.

Once you have calculated your planter’s litres, simply times it by 0.2-0.5, depending on how much compost you wish to add, to arrive at the quantity you need to buy.

Cubes and Rectangles

Calculating volume for cubes and rectangles is very easy. Simply multiple width, depth and height and then divide by 1000.

Hence, a 100cm³ planter would have a volume of 1000 litres. (100 x 100 x 100 / 1000.) A 140 x 30 x 30 rectangle would have a volume of 126 litres. (140 x 30 x 30 / 1000.)


Calculating the volume of a cylinder requires multiplying height by radius squared by pi which is written as V =πr²h. You then need to divide by a 1000 to get volume in litres. Hence a planter with 30cm diameter and 30cm in height would have a volume of 21 litres. (3.142 x 15² x 30 / 1000.)


To calculate the volume of a bowl, you have to calculate the volume of a sphere and divide by 2. Calculating the volume of a sphere requires multiplying 4 divided by 3 times pi times radius cubed, which is written as 4/3πr³. You then need to divide by a 1000 to get volume in litres. Hence a bowl with a 15cm radius would have a volume of 7 litres. (((4/3 x 3.142 x 15³) / 1000) / 2.)

If you would like to know more about soil science please read our guide: Everything you need to know about soil.

If you are interested in pots, Primrose has the biggest range online with over 2000 planters. We also sell compost starting at £5.99.

Jorge at PrimroseJorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!

His ideal afternoon would involve a long walk, before settling down for scones.

Jorge is a journeyman gardener with experience in growing crops.

See all of Jorge’s posts.

Jorge, Plants

Darwin’s illustration of the tree of life from On the Origin of Species.

The difference between genus, species, variety and cultivar is that each are different taxonomical ranks, containing populations of organisms with genetic similarities. These ranks reflect the ultimate goal of taxonomy, which is to lay out the tree of life, accurately documenting the relationships between organisms, both living and dead, tracing life back to a single ancestor. In this article, we seek to explain both why populations have been placed in certain ranks and the naming conventions used, which allow the easy identification of organisms.

Scientific name or species name – Prunus incisa

Comprised of genus Prunus and specific epithet incisa. Epithets usually refer to a feature of the plant (serrulata – little-saw, which refers to the shape of the leaves), but sometimes its origin (nipponica – Japan) or discoverer (sargentii – discovered by Charles Sargent). Genus is capitalised while its specific epithet is lower case italicized, just like its variety. Often genus is abbreviated to save time (P. incisa).  

Genus is the highest taxonomic rank you’d likely come across when browsing for plants. Genera are easy to learn. Prunus, for example, contains plums, cherries, peaches, nectarines, apricots and almonds.

Genera are hotly debated and sometimes revised. Taxons – a population of organisms – can be monophyletic, paraphyletic or polyphyletic. In monophyletic groups all species are descended from a common ancestor; paraphyletic groups contain all the descendents of a common ancestor minus one or more monophyletic groups; and finally polyphyletic groups are characterised by convergent features or habits of scientific interest. Today, taxonomists seek to avoid polyphyletic groups, believing taxons should reflect evolutionary relationships. Despite this, polyphyletic groupings persist, because of their usefulness to researchers studying similarities spread across evolutionary groups.

One recent study found that Prunus is monophyletic with all species descending from a single eurasian ancestor. Prunus, however, can be divided further into several subgenera. Historically these taxons would be based on morphology, although today they are often based on genetics. Thus subgenera are also disputed. An example of a subgenus is the Prunus subg. Padus that includes Prunus padus – a species of cherry native to the UK. As with genus, subgenus is also capitalised.

The scientific epithet completes the species name, distinguishing the plant from others in the genus. But what is a species? One definition states a species is a group of similar individuals which can reproduce successfully with each other while at the same time being reproductively isolated from other similar species. This definition leaves it up to scientists to decide when a group of individuals is distinct with some placing greater weight on genetics, others more obvious characteristics such as their morphology.

When a group of individuals becomes geographically isolated, it will begin to develop unique traits, making it distinct from the rest of the species. These distinct groups are known as varieties. Over time, they may become so different from the parent group that they are unable to breed, leading to the creation of a new species. Often, however, a variety come into contact with its parent group, resulting in an influx of genes that erodes their distinct features, reintegrating it into the greater species group.

Variety – P. nipponica var. kurilensis

The example in question, var. kurilensis is from the Kuril Islands – an island chain North of Japan, which is significantly colder than the Japanese mainland. It is extremely hardy and one of the few ornamental cherries suitable for the Nordic countries’ climate. Varieties are true to type as their seeds produce offspring with the same unique characteristics of the parent plant. Generally, plants aren’t advertised by their variety with nurseries preferring cultivars.

Cultivars are distinct from varieties in that they do not occur naturally in the wild. Cultivars are selected by humans for specific characteristics and are propagated through vegetative cuttings i.e. cloning. Propagation by seed will often lead to something different from the parent plant and as such they aren’t true to type.

Cultivars can be created through mutation breeding and hybridisation. Sometimes hybridisation programs can take years involving multiple crosses that each add a desirable trait as in the case of the Malus ‘Evereste’ – a cultivar resistant to fire blight, apple scab and powdery mildew. Mutation breeding involves bombarding plants with radiation as to induce mutations (new traits). An example of this is the ‘Rio Star’ grapefruit that is red in colour and produces more flesh and juice than varieties found in the wild. Cultivated varieties are more expensive than natural varieties due to the cost involved in development.

Cultivar – Prunus x incam ‘Okame’ / Prunus x incam cv. Okame

Cultivars are often capitalised and placed in single quote brackets, although sometimes they are written formally and preceded by an abbreviation. In the case of hybrids an x is placed before the second epithet as in the case ‘Okame’ that is a cross between the incisa and campanulatus.

If you are interested in learning more about taxonomy, please read our article: Plant Taxonomy: a History.

Jorge at PrimroseJorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!

His ideal afternoon would involve a long walk, before settling down for scones.

Jorge is a journeyman gardener with experience in growing crops.

See all of Jorge’s posts.

Current Issues, Jorge, Plants

A 1644 edition of Theophrastus’ Historia Plantarum.

Plant taxonomy, or systematics, is one of the oldest biological disciplines, tracing back thousands of years to when the identification of medicinal, edible, poisonous plants as well as those suitable for crafting would prove essential for survival and later man’s mastery over the environment.

Paradigmatic to history of science were the ideas of Aristotle, in particular the science of logic. This method influenced systematists who sought to identify the essence of living things by examining many specimens and discarding variable characteristics and establishing constant characteristics. This, of course, does not work well for biology with species exhibiting significant variation between individuals. Thus, improved understanding required the emergence of empiricists, who did not believe in the essence of each form.

Other early historic figures include Theophrastus and Dioscorides, who were both Greek, but lived hundreds of years apart in classical Greece and the Roman period respectively. Theophrastus wrote hundreds of manuscripts describing plants including two large botanical treatise Enquiry into Plants and On the Causes of Plants. His works are the first surviving documents to describe plant parts, reproduction and sensitivity to climate as well as classify them by their properties as medicinal, edible and herbal for example. Dioscorides travelled widely as a physician in the Roman army and classified over five-hundred plants by their medicinal properties in his five volume De Materia Medica. Unlike Theophrastus, whose work was lost to the West till the renaissance, Dioscorides’ pharmacopoeia remained the primary botanical text for nearly fifteen hundred years.

Aristotle made immeasurable contributions to numerous fields. Despite this, many of his scientific ideas were off the mark and became entrenched after becoming part of Church’s official doctrine, which sent thinkers down blind alleys and forbade freethinking.

It took to the 1600s for the next major advance in taxonomy with John Ray’s Methodus Plantarum Nova that published details of eighteen thousand species classified by their morphology – that is an organism’s form and structure. Previously, many taxonomic systems were arbitrary, sorting plants alphabetically or by their medical properties; although he has an interesting precursor in Andrea Cesalpino, who classified plants according to their fruit or seeds. Ray was devoted in his study of botany and based his system on all of a plant’s structural characteristics, including internal autonomy. He was also a cleric and can be viewed as an early parson-naturalist who saw science as an extension of his religious work, with God wishing for man to understand his creations by collecting and classifying organisms.

Next came Joseph Pitton de Tournefort’s Eléments de botanique, ou Méthode pour reconnaître les Plantes that while not particularly original and somewhat flawed was both well written and structured and would prove highly influential as an educational textbook, especially for the father of modern taxonomy Carl Linnaeus.

Linnaeus proved revolutionary, creating the taxonomical system in use today, laid out in the works Systema Naturae and Species Plantarum. He established the binominal system of nomenclature – that is, the use of a two part name for each species, consisting of the genus name and scientific epithet. This proved a huge advance over the long, excessively descriptive names used previously such as Rosa sylvestris inodora seu canina and Rosa sylvestra alba cum rubore, which now read simply as Rosa canina. It was in fact essential with the massive influx of species originating from the hitherto unexplored regions of Africa, Asia and the Americas in need of classification.

(These older names were influenced by the Aristotelian definition of form, split into genus – the general thing described – and the differentia, which gave its special characteristics. The major problem with this was as more species were discovered the differentia became longer and longer, hence the impractical name for the dog rose above.)

John Ray saw the natural world as static, its wonders evident of intelligent design.

The publication of Charles Darwin’s The Origin of Species and his theory of evolution would again prove paradigmatic. Classifying plants by their morphology was clearly limited as organisms can possess similar characteristics but be unrelated. It was now the task of systematists to use classifications to reflect evolutionary history, placing closely related organisms together, and identifying unique species.

It wasn’t until the 1960s that systematists could accurately classify organisms according to their evolutionary history with the work of Walter Zimmerman and Willi Hennig in the preceding decades that established an objective criteria for determining the shared genetic attributes of living and fossil organisms. It was in this decade also that revolutions in molecular biology provided methods for determining the molecular structure of proteins and amino acids. It was techniques such as these that allowed systematists to supplement their analysis by comparing organisms’ genetic codes and identifying changes in genetic code.

Today systematists use multiple sources of evidence to establish a plant’s evolutionary history such as morphology, biochemistry, paleobotany (plant fossils), physiology (internal activities – i.e. photosynthesis), ecology (plants and their environment), biogeography (plant distribution), and molecular systematics (analysis of genetic code). This has been enabled with advances in computing that have allowed the analysis of large datasets.

Carl Linneas characterically posing with a plant.

Scientists estimate that there are ten to one hundred million species, so establishing their evolutionary history is a monumental undertaking. Currently, plant taxonomy is controlled by the International Codes of Botanical Nomenclature (ICBN) published by the International Association of Plant Taxonomy (IAPT), who revise codes at every International Botanic Congress. It should be stated that even with all the advances in understanding, scientists still disagree how to best classify organisms. For example what is a species?

One definition, known as the Biological Species Concept, defines a species as a “group of similar individuals which can reproduce successfully with each other while at the same time being reproductively isolated from other similar species”. The problem with this is identifying the point at which a particular population is distinctive from its parent species, as there are infinite possibilities to choose. Another definition, known as the Phylogenetic Species Concept, places more weight on the genetic differences between populations and their evolutionary history. Again the problem with this is that scientists can identify numerous genetically distinct populations, greatly increasing the number of known species.

To conclude, plant taxonomy is an ongoing project that will likely never end due to divisions about the importance of a particular characteristic and the discovery of new species and fossils. Nevertheless, the work to date has produced a logical system of classification that makes identifying plants and their relatives relatively easy.

If you would like to know more about the challenges of classification a great overview can be found here. If you would like a simple overview of the classification of plants, a table can be found here. If you would like to know more about taxonomy, especially the ranks you are likely to come across  when browsing for plants, please read our article: What is the Difference Between Genus, Species, Variety and Cultivar?

Jorge at PrimroseJorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!

His ideal afternoon would involve a long walk, before settling down for scones.

Jorge is a journeyman gardener with experience in growing crops.

See all of Jorge’s posts.