Garden Design, Gardening, Jorge, Plants, Watering

Reducing water use in the garden is a no brainer as it saves both the environment and money, leading to lower energy bills. Surprisingly, for a country with supposedly so much rain, the UK’s water supply is under severe stress due to excess demand that has taken its toll on our rivers. This year, there are fears the UK could be heading for a summer drought with rainfall in April 50% below average.  To solve this problem we need to improve water efficiency and doing so in the garden can be extremely enjoyable as it requires nous and experimentation.

Create a water thrifty garden

I recently visited the Cambridge University Botanical Garden, and saw a section comprised of plants that require no watering. The accompanying material described the fascinating ways plants have adapted to arid environments, such as how species of cacti reduced their leaves to spines and adopted spherical forms as to lower their volume to surface ratio, decreasing water loss.

Scientists have identified four strategies such plants use for coping with drought: escaping, evading, enduring and resisting that is described in detail here. Put succinctly, the first two strategies involve restricting growth and reproductive activities to the wet seasons, while the latter two involve reducing transpiration and growth (often through restricting photosynthesis) as to subsist in the heat.

Various morphological and physiological adaptation have allowed cacti to be extremely frugal in their usage of water.

Your own water thrifty garden (or section of the garden) doesn’t have to be made of just succulents or cacti, but can include many familiar plants, and even crops, creating a garden rich with colour and form, but with less maintenance. There are lists of drought resistant plants online and there is great guide to designing a stunning water wise gardens that can be found here.  

Creating such a garden will involve a some trial and error, but there some general practices that can be followed:

  • Permeable paving is a must as it allows water to percolate into the soil below, feeding your plants’ roots. With non-porous materials water will sit on top and evaporate.
  • Divide your garden into hydrozones with plants with similar water needs together. This will allow you to water more efficiently.
  • By using less fertiliser, your plants will grow slower and use less water.
  • Water less, but thoroughly, watering the entire root system. You can gauge how well the water is penetrating through pushing a pipe into the soil (it will move more easily through wet soil).
  • Sometimes it can be difficult to gauge when to water. This can be ascertained by digging into soil. If the soil below the topsoil is moist, there may be no need to water. If it is dry, it’s time to water. It is important to factor in certain soils such as sandy that will feel more dry and clay that will feel more damp. Although, the ultimate measure is your plant’s leaves: darkening or drooping may indicate water stress.
  • Gauge your soil type. Some soils (clay) are better at holding moisture, and can be watered less frequently (but with more water), while others will need frequent watering (sandy soils).
  • Water in the morning and evening when less water will be lost to evaporation.
  • Dig channels, basins, or funnels to avoid run off.
  • Mulching, either with organic or inorganic materials (gravel) will help maintain soil moisture and protect soil life from the sun’s rays.
  • Forgo turf. A perfect lawn is difficult to maintain and will require constant watering in the summer months.
  • Funnel rainwater from your roofs to waterbutts. A simple modification to your guttering will provide much needed water in times of drought.
  • Much of the water your household uses is good to reuse in the garden. Greywater recycling has the additional advantage of reducing the water sent back to water companies, which sometimes ends up in rivers, destroying the ecosystem.
By far the best way to reduce water use, this simple modification to your drainpipe will provide thousands of litres of water year on year.

Hügelkultur beds

Hügelkulturs are raised beds constructed from rotten logs overlaid with organic matter and soil. They aren’t enclosed and therefore slope; henceforth the name: hill/mound (hügel) culture (kultur). Hügelkulturs can significantly reduce water use as the decaying wood acts as a sponge, soaking up rainwater that it slowly releases back into the soil. The beds are so effective that after the first year, there will be no need to water your crops for many years, provided the bed is of a certain size.

Constructing a hügelkultur is relatively simple, but they have to be of a certain height (between two to six feet). The height is important as it determines how effective it will be at holding water. In general, a six foot bed will require no watering after the first year, while a two foot one will hold moisture for three weeks. Upon construction, a bed will begin shrinking, and a seven foot bed will become six foot, so they should be constructed higher than the desired height. To avoid excessive compaction of the soil, and to maintain good aeration, it is recommended that you build your beds with steep sides (45 degrees).

A hugelkultur bed with cds to scare away birds. Picture credit: Maseltov (2005) licensed under CC-BY-SA 4.0.

Certain trees are unsuitable as some trees are allelopathic, that is, will harm your crops with allelochemicals that will persist in the soil. Others take too long to rot. Most tree logs should be fine, and there are lists of allelopathic trees and scrubs online, so do some research. Known trees to avoid include include cedar, black locust, black cherry and black walnut. Excellent species to use include alders, apple, cottonwood, poplar, willow, and birch.

Before building your own bed, it is worthwhile to decide on whether you want to construct it entirely above ground or in a shallow trench (about two feet deep). The latter, lower in a ditch, will not impose on the landscape and will be easier to construct. (Try throwing soil six feet high!) It will also save on digging, as you can reuse the materials acquired when digging the trench, and not dig up other sections of the garden. Building above ground is preferable if you already have materials on hand, or find digging difficult. Constructing on top of sod has the additional advantage in that once the plant matter breaks down it will produce nitrogen for the soil.

hügelkultur beds

Once you have decided upon the above, simply pile your rotten wood, whether it be logs, sticks, timber or chippings, with the biggest at the bottom. Then give it a good drenching. (This will aid decomposition.) Fill in the gaps with kitchen waste, grass, leaves and manure. (Adding organic matter is useful as during decomposition wood will both take in, and then release nitrogen, so it is possible that the soil may be nitrogen deficient at points.) Then add a layer of sod upside down. (You can acquire turf when building a trench. If you have none, just use soil.) Next comes more soil as so the wood is fully covered. The degree the wood is encased is a matter of preference, although anything from a few inches to half a foot works best. Finally, top it off with mulch such as straw that is traditionally used.

Now your hügelkultur bed is complete, it is recommended that you start planting to prevent erosion. (Henceforth, it is useful to construct in time for the growing season.) Over time the wood will decay into rich humus, but at first, the soil will be fairly dense, so certain crops may be unsuitable for planting in its first year. Great crops to plant in this time include members of the cucurbitaceae family such as squash, melons and pumpkins.

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.

Allotment, Composting, Gardening, Grow Your Own, Infographics, Jorge, Planting

Crop rotation is essential for any gardener who wishes to grow their own food as it greatly increases one’s vegetable yields. All it involves is rotating what you grow between plots as to maintain nutrient levels. The most common way to do this is by rotating four families of crops that complement each other. By waiting four years before growing vegetables from the same family in a particular plot, one can partly restore the soil’s nitrogen content, and avoid the buildup of disease/pests. The most simple way to do this is to use four equal-sized raised beds and rotate clockwise.

Crop rotation has long been practiced and even features in the Old Testament. After the advent of farming, farmers came to realise that growing the same crops year-on-year would exhaust the soil, so it became common to leave fields to fallow once every two years. By the Middle Ages a three-field system was developed, whereby legumes such as beans, lentils and peas were introduced and grown after nitrogen-hungry cereals.

The introduction was of great importance as the legumes can both thrive in nitrogen-depleted soil and restore the quantity of nitrogen for future use by cereals. Legumes are unique in that they form symbiotic relationships with nitrogen-fixing bacteria, exchanging carbohydrates for nitrogen. The bacteria acts to improve the soil as once it dies the nitrogen eventually becomes mineralised, available for use by bacteria, fungi and plants.

Charles “Turnip” Townshend introduced four field rotation to England.

From the 18th and 19th century, more advanced forms of crop rotation substantially increased agricultural output, partly enabling the growth of cities and the Industrial Revolution. Originating from Holland, came four-field rotation that was introduced to England in the 18th century by Charles Townshend. Townshend divided his fields into four different types with a different type of crop grown in each. The system allowed farmers to keep all the fields in use, and utilised clover, another legume, to improve the soil’s nitrogen content. Also grown was turnips that along with clover was used as a source of fodder. More nutritious than grass, the fodder produced healthier livestock, and richer manure that could be plowed back into the soil. By growing animal feed every year, livestock no longer needed to be slaughtered over winter, increasing their quantity and quality.

The benefits of crop rotation has been confirmed with multiple modern scientific studies. One recent study from the John Innes Centre found that growing peas and oats in soil that previously grew wheat significantly increased the diversity of microbes, which help plants acquire nutrients, regulate growth, and protect from pests and disease. Another from 2012 found that “grain yields, mass of harvested products, and profit in more diverse systems were similar to, or greater than, those in the conventional system, despite reductions of agrichemical inputs”. And finally, a study from 2009 found that organic sources of nitrogen (i.e. legumes) remained in the soil for longer than inorganic sources, reducing the pollution of water sources from run-off.

So, what plants should I grow in my beds? Presuming you are to practice four-bed rotation we recommend that of the six main vegetable families: potato (Solanaceae), pea (Fabaceae or legumes), cabbage (Brassicaceae), carrot (Umbelliferae), beet (Chenopodiaceae) and onions (Liliaceae), you grow them all separately with the exception of onions, carrots and beet that can be all grown together. By rotating between different families, you can avoid build up of disease/pests that tend to attack specific plant families, and grow a variety of different crops. In general, it is best that peas (Fabaceae or legumes) follow the nitrogen depleting potatoes (Solanaceae). This will help you maintain healthy soil. Simply plan out what you wish to grow.

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.

Gardening, Jorge, Weeding

To many gardeners, weeds are a recurrent annoyance that you have to put up with as a fact of life. They can interrupt your otherwise perfect lawn or stifle your crop yields, and at worst cost thousands of pounds in damage as in the case of the Japanese knotweed. The effects of weeds are extremely costly, and it has been estimated that up to 10% of agricultural production may be lost because of them. But, weeds play a key role in transforming inhospitable environments into new habitats, and without them we would not exist today.

Weeds are good for the ecosystem

Weeds are important as they play a key role in transforming barren earth into rich fertile soils. They are, in effect, pioneers as the first plants to colonise a piece of land and improve its soil for the development of more complex ecosystems. They do this in a number of ways.

Weeds act to shield the soil from the sun, protecting both insects and microscopic organisms from sunlight. Their roots stabilise the soil, creating a secure environment for life, while their stems trap organic matter, which breaks down in the soil and provides sustenance for insects. Weeds with long roots draw up nutrients from deep in the ground, improving the quality of the surface soil. When they finally die, they decompose into humus which increases the soil’s moisture and nutrient retention, but decreases its bulk density, which is important in the early stages of soil development.

Curled Dock with its deep taproot draws up nutrients to the surface soil. Picture Credit:  Oliver Pichard (2007) licensed under CC BY-SA 3.0.

Back hundreds of millions of years ago, the Earth was very different, as a barren rock with water running over the surface with no defined course. Key to transforming the Earth were plants that broke down rock into minerals and soil, which it then held in place with its roots. This led to the development of river banks that channeled water in a regular fashion. Periodically, such rivers would flood, depositing sediment over large areas, which allowed trees to take hold. Such larger plant life would produce even more debris that would block up rivers, causing more flooding, a process that would lead to the emergence of larger complex ecosystems.

The predecessors to the plants that we consider weeds today played a key part in all this as early pioneers that ensured soil stability in such flooded areas. Important to this were rhizomes that allowed plants to cope with severe disruptions in their environments. Rhizomes are branching stems that grow horizontally, often through the soil, and are the feature that makes weeds so durable, as even if you destroy a plant’s matter above ground any surviving rhizome in the soil will lead to its reemergence. Not only does the rhizome store energy, allowing a plant to reemerge in favourable conditions, the stems allow the plant to propagate vegetatively,  producing a clonal plant.

An artist’s (Édouard Riou) impression of early Devonian land flora.

One early example of a plant that helped stabilise the earth’s environment was the Drepanophycus from the Devonian Period, which was unearthed by a team from Peking University. It was discovered preserved in paleosols – fossil soils – that within were multiple sequences of sediment formed by river channels, which were periodically wiped out by floodplains. The plant grew continuously due to its rhizomes and trapped sediment, enabling stable soils to develop. And after the floods, the plant would reemerge, growing through the newly deposited layers of sediment. The team calculated that the plant had a modest, but significant role, in reducing soil erosion. It is believed to have carried out this function for centuries.

Today, many plants we consider weeds play an important role in the ecosystem. Weeds native to the UK provide food and shelter for numerous animals, especially pollinating insects, which are essential for crop yields. Many species of butterfly, for example, lay their eggs on nettles including the beautiful Red Admiral and Painted Lady. Keeping their habitats intact will be essential to prevent the UK’s insect population dwindling further.

Weeds constitute an interesting case study in evolution and humanity’s effects on the environment

Today weeds constitute a fascinating area of study due to their phenotypic plasticity, or simply put, their ability to change in response to changes in their environment. An example of phenotypic plasticity may be a plant’s ability to utilise more or less water (in photosynthesis) depending on its availability. Phenotypic plasticity is especially important for plants that do not have the ability to change their environment (as in the case of many animals, such as humans), and weeds are especially adaptive as agricultural practices make it necessary to be highly responsive if they are to survive.

Weeds evolve quickly in three principal ways: through adapting to continuous habitat disturbance, emerging in part from agricultural practices; through reproducing with different cultivars (groupings of plants selected for certain characteristics) as to produce hybrids; and finally through returning to natural seed dispersal methods when certain domesticates (plants dependant on humans for survival) are abandoned. This has led to the survival of certain species that are extremely difficult to control as they have developed such traits as early germination, rapid growth from seedling to sexual maturity, and the ability to reproduce both sexually and asexually. Fascinatingly, a 2013 study carried out by Fudan University of Shanghai found that if genetically modified crops did crossbreed with their weedy cousins, the resultant weeds would have higher rates of photosynthesis, more stems and flowers, and significantly more seeds. So, in the future, weeds may become even more troublesome than they are now.

Centuries of grazing has altered the landscape, benefiting plants that can’t be consumed by livestock.

As such, the battle between farmers and weeds constitutes an interesting case study of evolution in action and the selection effect humans exert on plants. There are many examples of the latter. For example, tilling tends to favour annuals at the expense of perennials, while no till systems benefit perennials. Frequent mowing, on the other hand, tends to benefit weeds that grow horizontally. The grazing of livestock has led to an increase in noxious thistles and other inedible species on the rangeland. In some cases, weeds have even begun to replicate crops in their appearance and life cycle as in the case of barnyardgrass growing with rice.

Weeds perform an important signalling function

Weeds can tell you a lot about your garden, providing information about what is best to grow. If your weeds multiple rapidly it is likely that your soil is extremely fertile, and that you do not need fertiliser. If not, it may be wise to start growing forerunners such as onions before moving onto more difficult crops. If the amount of weeds is diverse, it is likely that you can grow a wide range of plants in your garden. If not, it will be worthwhile to ascertain the soil type. And weeds can do this too. Very acidic soil will produce sorrel and plantain but no charlock or poppy, while chickweeds is sign of neutral pH. High levels of nitrogen can be ascertained by nettles, ground elder, fat hen and chickweed. Compacted soil is noticeable for silverweed and greater plantain, while creeping buttercup, horsetail and silverweed may indicate wet soil with poor drainage.

Weeds constitute a good source of nutrients

Dandelion leaves are high in vitamin a and k and can be useful addition to a balanced diet.

Many weeds are edible and good for you. They are also effectively free and environmentally friendly. In the UK, nettle soup comes to mind as one famous example. Back in the Middle Ages, ground elder was grown as a crop and was believed to cure gout – hence its alternative name goutweed. It possesses a nutty flavour and can be added to salad. Many health blogs recommend dandelion as a superfood, which can be found everywhere. Sorrel and horseradish can both be made into sauce and the latter is often used with beef. There are many great blogs dedicated to eating and cooking wild food. Why not check them out for yourself?

A concluding thought

Perhaps, our obsession with weeds tell us more about ourselves than we think. Why are we pursuing them with such vigour? Instead of hastily striving for a perfect world without weeds, perhaps we should examine why they are there in the first place. After all, a weed is a plant whose virtues have yet to be discovered (Emerson, apparently).

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

Green plants appear green due to a pigment called chlorophyll that primarily absorbs blue and red wavelengths of the visible light spectrum, but reflects a portion of green wavelengths. This green light enters our eyes and hits the light-sensitive retinas, in which there are cone cells, that once stimulated, sends a signal to our brain that interprets the information, giving the colour green. Therefore it can be stated that the colours of an object is dependent on what colours are reflected (or transmitted) back to our eyes. (Technically speaking,  visible wavelengths have no colour. Colour is created in the brain.)

Most humans are trichromats, and possess three types of cone cells sensitive to red, green and blue light, named L M and S respectively. Each cone allows us to distinguish around a hundred shades, so the total number of combinations is at least a million. Colour is determined by our brains that interpret the different ratios of these three colours.

The visible light spectrum ranges from approximately 400nm to about 700nm. Our brain attaches different colours to different wavelengths with blue at about 475nm, green at about 510nm and red at about 650nm. Picture Credit: Vanessaezekowitz (2007) licensed under CC BY-SA 3.0.

Not all humans, or all animals, perceive colour in the same way. Dichromats, such as dogs, possess two types of cone cells and can distinguish blue and yellow, but not red and green. Their vision is similar to some colour blind humans, who only have two working cone cells due to either an absence or a malfunction of a third type of cone cell. Not all colour blind humans are the same as they can have different combinations of working cone cells (or none at all), and thus are unable to see different colours, resulting in different colour spectrums.

Some animals are tetrachromatic and able to distinguish to four primary wavelengths of light. Birds, for example, are even able to view ultraviolet light, which is beyond the visible light spectrum. (Interestingly, humans with Aphakia can also view ultraviolet as their lens has been surgically removed. For the rest of us, our lens blocks this light.)

Some women are tetrachromatic as they possess four types of cone cells, which allows them to see a hundred million colours. The extra cone cell has its origin in their fathers’ colour blindness, who possess two working cone cells and one mutant one. This mutant one is passed on to the daughter, who then has four cone cells. It is probable that tetrachromats have to train themselves to see such an array of colours, as the natural world will not have such a diversity of colours for the brain to learn to use the fourth cone. As such, it is likely that most will go through life without recognising their potential.

The absorption spectrum of a bird’s (Estrildid finches) four cone cells.

So tetrachromats, both human and non-human, can distinguish many more hues of green than  the rest of us, and plantlife may appear very different. For animals like birds this may be very useful for distinguishing between plants to find sources of food or shelter.  For the rest of us, our trichromatic vision proves very useful in allowing us to quickly identify between opportunities for profit and sources of danger, such as when fruits are ripe.

Plants need to absorb light in order to carry out photosynthesis to produce glucose, which can be used for metabolism and growth, or stored as starch. Photosynthesis is a chemical reaction that inputs sunlight, water and carbon dioxide and outputs glucose and oxygen. It is a two step process, comprised of light-dependent and light independent reactions. In the former sunlight plays a key role by providing the chlorophyll with energy to kickstart the complicated chemical reaction.

In green plants, there are two types of chlorophyll: chlorophyll a and chlorophyll b that both absorb different spectrums of light. They both complement each other with a absorbing more red light and b absorbing more blue, and this allows the plants to fulfil its energy requirements. As you can see in the graph below, chlorophyll still absorbs green light but not to the same extent as they do red and blue.

Picture Credit: Daniele Pugliesi (2008) modified by M0tty licensed under CC BY-SA 3.0.

However, this is not the full story. The above graph represents the absorption spectra of extracted chlorophyll molecules. As part of a plant, chlorophyll never exist alone but are bound to molecules that influence what it absorbs, and as such plants absorb about 70% of green light.

There are other pigments (accessory pigments) inside green plants that play a role in photosynthesis such as carotenoids. They primarily absorb green and blue, but reflect yellow, orange and red. It is these pigments that give many plants’ leaves their autumnal colours, and signal the presence of ripe fruit, once the amount chlorophyll is reduced. These accessory pigments are useful as they allow the plant to capture more of the sun’s energy by broadening its absorption spectrum.

So, what about plants that aren’t green? While all plants that photosynthesise contain chlorophyll a, they can contain many different types of accessory pigments, giving them different colours. For example, many reddish-purple plants contain the pigment anthocyanin in such abundance that acts to mask the green chlorophyll pigments.

So, why do plants use red and blue light more so than green? And why do they not absorb all visible light (and henceforth appear black)?

It is believed that today’s plants evolved from a common ancestor (green algae) that used chlorophyll to photosynthesise. Why no alternative dominant pigment emerged is an unanswered question, although many hypotheses have been proposed. Evolution is a product of multiple processes such as random mutation, random selection and natural selection, and henceforth plants can’t design or choose the best pigment to use. It is therefore probable that once chlorophyll proved successful no new alternative dominant pigment emerged, thus enabling green plants to dominate the landscape. Although, there is a possibility that (primarily) utilising a narrow band of wavelengths (red and blue) for photosynthesis is mechanically superior, and this allowed early organisms to outcompete other lifeforms.

For more discussion on why plants use chlorophyll, and are henceforth green, can be found here, here and here.

Why do plants use the visible light spectrum for photosynthesis?

In general, plants only absorb trivial amounts of light outside of the the visible light spectrum. This is because the sun produces the most light in the visible light spectrum, and chlorophyll have evolved to utilise it. (If you look at the graph above, chlorophyll a’s absorption spectrum is almost exclusively confined within the visible light spectrum.) There are other mechanical reasons for this. Visible light is perfect as it provides just enough energy without causing damage to the plants’ cells. By contrast, ultraviolet is damaging and infrared contains insufficient energy. In addition, a lot of ultraviolet light is blocked by the ozone layer.

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.

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