The importance of mulch

There is one job I rate as more important than any other in the garden; mulching. The application of a thick layer of organic matter to your beds will have multiple benefits and the garden will reap the benefits for years to come. 

At the moment, the leaves are still falling and the trees and shrubs are applying a thick layer of their own organic matter to the beds, but this will soon slow down. Now that all my bulbs have been planted, and the leaves will soon be cleared (where necessary) I will spend the next few weeks giving all the beds a dressing of composted bark mulch. This has many benefits for the soil. The thick layer of organic matter will act as a blanket, retaining warmth and keeping its biological processes at work long into the winter. It will provide protection from the erosion and leaching caused by winter storms. The blanket effect will also help to reduce the number of weed seedlings that appear as the soil warms again in the spring. Over the next 12 months it will gradually be incorporated into the soil by worms. Mulches generally have little nutrient content to add to the soil, but they will slowly improve the structure of the soil, making it less prone to compaction, able to retain more moisture, and making the ideal home for an even more diverse selection of beneficial fungi and bacteria.

It doesn’t just have practical benefits. After the storms of autumn have taken their toll on the borders, this is the ideal opportunity to dress the garden. The recent frosts have meant tender annuals and soft-stemmed perennials have melted into an indistinguishable sludge leaving just the sturdier plants with their handsome winter outlines and attractive seed heads. Filling in the gaps in the border with a protective coating of mulch provides a uniform background to display all those structural plants to their absolute best.  

There is a huge choice of substrates that can be used for mulching. My personal favourite is composted bark. It is light, easy to spread evenly, conditions the soil beautifully and is relatively inert, so you wont get a huge bloom of weed seedlings on top of it. On the veg patch I like to use the well-rotted compost from the bottom of our enormous heap. It doesn’t contain as much nutrients as animal manure, but it does provide some nutrition, and will quickly bulk up the soil. In the hot, Mediterranean garden we apply a layer of limestone chippings each spring, which don’t provide much in the way of nutrients for the soil, but are excellent for improving drainage and reflecting heat, meaning it is consistently the warmest part of the garden.

On amenity plantings, coarse bark chippings are often used as they breakdown much slower and will protect the soil from wear and compaction for a longer period before they need to be replaced. Mushroom compost is a popular option for veg growers. This is an animal manure which has been processed, then used for growing mushrooms. It is high in nutrients and excellent for the veg patch. I have also previously used recycled green waste on my allotment. You need a sharp eye to watch out for any household items which may have made it through the composting process but, apart from the teaspoons, it certainly helped to improve the soil structure. I have also used strulch, a mineralised composted straw. It takes a while to break down, and the minerals can affect the nutrient balance of the soil if used over a long period, but it does give a very even appearance, and is very light to move and spread.

Recently, I have become interested in the idea of using plants as ‘living mulches’. The use of green manures has gained momentum in recent years. In the winter, rather than leaving soils bare, or covering in manure, a secondary crop is sown, grown, then dug into the soil just prior to the next planting season. Legumes like beans, phacelia or clover are popular for increasing nitrogen, and mustard has become popular to act as a ‘soil sterilant’, reducing the incidence of pests and diseases. The climax of this idea must be the techniques advocated by Japanese horticultural researcher Masanobu Fukuoka in his book “The One-Straw Revolution”. In the book he describes his natural system of farming. Cereal crops such as rice, root crops like radish and vegetables such as squashes, are sown in mixed fields using clay pellets, through a living mulch layer of legumes like clover that feed the crop as it grows. When the field is harvested the waste straw is left in the field to compost where it grew, and the next crops are sown directly through it. The system tries to mimic natural systems as closely as possible and it was claimed that his farm achieved yields comparable to his neighbours with no inputs of fertiliser or any use of pesticides. As yet, I haven’t yet been able to initiate a ‘one-straw revolution’ system on my allotment beds, and I’m not entirely sure the allotment committee would look benevolently on such an experiment, but over the next few years I am hoping to see how I can use the principles of this system to inform my own growing, and hopefully find a way to make my plot as self-sustaining as possible.

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Jack Frost pays a visit

Over the course of the past couple of weeks, Jack Frost has paid a couple of visits to the garden, decorating everything with a fine dusting of ice crystals. From the mild, dry and sunny days of early autumn, we have moved into a colder and wetter phase of the year. Last week we reached the milestone of the first frosty morning since the spring. 

The short, sharp, shock of a cold and frosty morning can initially be exciting and invigorating. This soon gives way as the cold begins to penetrate and chill the bodies extremities. I quickly realise that like the squirrel, busy collecting and storing his nuts for the winter, I must set about my tasks with urgency, if only to keep the blood flowing and my feet and fingers from frostbite. 

Frost will form on surfaces when they have been chilled below 0c. The water moisture in the air condenses on the surface and freezes to form ice crystals. The extent of this chilling, the moisture content of the air and the speed at which the moisture condenses all effect the eventual appearance of the frost. A ‘hoar frost’ occurs in a moist atmosphere when a surface has been quickly chilled to several degrees below freezing, and refers to the way everything appears to be coated with a thin layer of white hairs. 

This severe drop in temperature signals the end of the road for the tender, frost-sensitive plants. Their leaves will blacken and wither, quickly turning to a slimy mush when the frost lifts later in the day. It is time to move the summer annuals to the compost heap and lift the dahlia tubers so they can spend the winter somewhere slightly warmer.

For more tender plants like bananas, we have hopefully managed to pre-empt the arrival of the cold weather, and they are now wrapped up cosy inside layers of straw, hessian or fleece, gently slumbering until the return of the spring rouses them once again.

For some plants, this colder weather will bring out their best. For roots like carrots or parsnips, and brassicas like cabbage or Brussels sprouts, the cold weather will prompt them to turn the starch in their cells into sugar. The increased concentration of sugars in the plants fluids lowers their freezing point, acting like a simple ‘anti-freeze’ solution, but also greatly improving their flavour. 

Many of our native tree seeds need a period of cold weather followed by warmer temperature, known as stratification, to grow. This process of freezing and thawing breaks dormancy of the seed and kickstarts the process of germination.

Whilst it is damaging for some plants, a period of hard frost can be good for others. The cold may help to reduce populations of some fungi, bacteria, viruses and insects that need living material to continue their lifecycle.

The trees are now shedding their summer coat of leaves, and before long they will once again be bare. There is a unique beauty to the stark reality that this part of the year presents us with. It isn’t often that we have the opportunity to see the bare skeleton of the garden, stripped of all its summer decoration. It is a chance to see the structure of every tree and shrub. A chance to make plans, plant bulbs and order seeds to fill the bare spaces next year. The pace of work in the garden changes and I find I now have time to spend focused on just one area. I know that every hour I can spend working on the garden now, will repay itself tenfold next year, when I will once again be overwhelmed by the pace of spring and summer as they hurtle by.

If it were not for the cold days, I know that I would certainly not appreciate the warmer days as much when they finally do return.

The allure of the exotic

Whenever I go abroad I find myself fascinated with the local flora. I have lived all of my life in the UK so I can wander around my local area and am confident I can identify many of the native species, as well as a lot of the cultivated ones. 

When I go on holiday and find myself outside of my local patch it becomes much more complex. Even the most common of plants seems alien to me. I am caught in a mix of uncertainty, as I no longer have the confidence to identify what surrounds me, but also excitement at the prospect of learning a whole new vocabulary of plants. Usually by the second day I am wishing I had purchased a good identification guide before I came, and am rapidly burning through my data, furiously googling to see if I can get a rough idea what the strange plants that have been bamboozling me are.

Last weekend I arrived back in the UK from a week of visiting my wife’s family in Israel. In between trips to meet the relations we managed to ‘shoehorn’ a couple of botanical excursions in our itinerary to satisfy my plant curiosity. We visited the botanical gardens in Jerusalem, had a nosey around a local garden centre, paid a quick visit to the immaculately maintained, neo-classical, Bahai Gardens on Mount Carmel in Haifa, and had a tour of the wonderful Hula valley nature reserve, a vital site for migratory birds.

Touring the botanical gardens set my mind racing. I was like a kid in a sweet shop, in awe of the huge collections of plants from all over the world gathered there. It was peculiar to see plants we are so familiar with, like oaks, apples or pears grown as ‘exotics’ outside of their normal habitat. The reduced moisture and the intensity of the sun meant they were more wizened and gnarled, and didn’t quite look the same as we expect to see them when they are grown in the UK. The large collection of plants native to the region was impressive, but I was most impressed by plants such as the collection of Banksia, which are from Australia and were positively thriving in an environment similar to their native home range. 

The desire to grow plants beyond their native range seems inherent in almost all gardeners and we have been doing this for centuries. Many plant hunters such as George Forrest, Ernest Wilson or Robert Fortune who have been immortalised by their introductions, were paid a tiny fee in comparison to the huge risks they faced to bring back seeds of exotic plants from the far reaches of the world. It wasn’t until the invention of the ‘Wardian case’ (a small, portable greenhouse) in the middle of the 19th century, that there was even any guarantee of bringing back specimens alive. I suspect that those explorers were not driven by ideas of riches, fame and glory through their discoveries, but by an innate fascination with the world around them and an all-encompassing desire to know more about it.

I am just as guilty as them. Whilst I will not undertake stripping a whole valley of rare orchids just to stop my rivals discovering them, I often find myself collecting a small handful of seeds from any interesting plants I spot, then slipping them in my back pocket to try and grow them at home. 

They may prove to be successful. I have managed to grow ferula communis (a giant form of fennel) I collected from an abandoned army base in Malta, and echiums, which were collected from a front garden in Tenerife. When they thrive I am provided with a happy and lasting reminder of the fun I had on my holiday. If they don’t, then at least I have learnt a bit more about the plants of that region on my journey.