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How to Grow Perennial Vegetables
By Martin Crawford, Marion Smylie-Wild
Green Books LtdCopyright © 2012 Martin Crawford
All rights reserved.
Why grow perennial vegetables?
Most gardeners who want to grow some of their own food have a combination of annual vegetables and fruit bushes and/or trees, but few have perennial vegetables (apart from, perhaps, rhubarb). This seems such a shame, because there are some fantastic food plants out there with delicious flavours that are often very easy to grow.
What is a perennial vegetable?
For the purposes of this book, a perennial vegetable is defined as a plant that lives for at least three years, and is raised for some edible part of it – such as the leaves, shoots, leaf stems, roots or flowers. The edible part might be used raw or cooked. The plant must also be capable of being harvested without killing the plant itself. You'll also find some well-known fruiting plants included here as a vegetable – strawberries, for example. These are included only if a part other than the fruit can also be eaten.
There is a distinction, rather blurry, between a vegetable and a herb. A herb (in the culinary sense) is a plant with a strong, distinctive taste, used as a flavouring in relatively small amounts. So I have not included, say, lovage as a perennial vegetable, even though it is perennial, and is edible. However, I do include some plants that we often think of as herbs if they can be used in bulk amounts in salads or cooked dishes – so you will find entries for some of the mints, and for sweet cicely.
In the context of this book, I am talking about plants being perennials in the climatic conditions found in the temperate and continental climates of Europe and North America. Some annuals of course become perennials if the climate is warm enough, and these are not usually included unless, like runner beans, they can be grown as a replant perennial (i.e. a plant that is perennial in a warm climate but in a cold climate can still be grown by lifting plant parts in autumn, storing them over winter and replanting in spring).
Also in this book are some replant perennials such as potatoes and mashua, where it is common practice to save some of the tubers in the autumn for replanting next year.
The case for growing perennials
There are lots of reasons why growing perennial vegetables makes sense.
You don't have to cultivate the soil every year. Turning the soil over takes a lot of energy, whether it is tractor energy in ploughing or human energy in digging. Because perennials are planted only once (or once every few years), you do not have to disturb the soil so often.
If you stop turning the soil, and keep on top of the flush of weeds you'll get from the initial soil preparation, then the weed seed bank in the top layer of the soil will not get replenished with deeper dormant seeds. You'll find that the weeding required decreases over time, especially if you mulch around your perennials.
Because most perennials do not need digging up every year, it is more important to weed out pestiferous perennial weeds when small. (When growing annual crops, the weeds can always be dug out in winter.) Nevertheless, even in the first year after planting, the weeding demanded should not be any greater than that for an annual crop.
Fewer carbon emissions
A few years ago, nobody considered what carbon emissions were resulting from agriculture and horticulture, but that is changing rapidly. Growing food and other materials creates a lot of carbon in the atmosphere, not least because almost all crops are short-lived, requiring the energy-intensive cultivating of soil every year. Cultivating the soil exposes soil organic matter (humus) to air both on the soil surface and in the soil itself, leading to release of carbon in the form of carbon dioxide.
Once you stop digging soil, carbon emissions are vastly reduced, and quite possibly reversed – you may start to actually store more carbon in the soil. This is because certain fungi (mycorrhizal fungi – see page 42) are critical in storing carbon in soils, and soil cultivation kills them.
Better for the soil
When you stop digging the soil and grow perennial crops that cover and protect the soil, the soil structure is maintained, which in turn helps everything growing in it. Soil humus levels build up, nutrients don't wash out so easily, and water is retained in drought, yet drains in very wet weather.
If you think about it, annual plants are not very widespread in the natural world. They appear whenever soil is disturbed by animals, plants falling over, and so on. But they persist for only a year or two before they are succeeded by perennial plants. In nature, most plants are perennial, and in basing our whole civilisation on short-lived plants we may have been down a productive but nevertheless destructive cul-de-sac.
Most perennial plants contain higher levels of mineral nutrients than the common short-lived plants grown as vegetables, which is not surprising really, considering that they have larger and permanent root systems, able to exploit soil space more effectively and thus take up more nutrients.
Vitamin levels in perennial vegetables are more variable, but can certainly be as high or higher than those in short-lived vegetables, even those known for high vitamin levels.
Protein levels in green vegetables can be high, and the protein content of perennial vegetables is frequently higher than that of annuals and biennials.
Extension of the harvesting season
Short-lived crops are distinctly seasonal. How seasonal depends on your climate, mainly on how cold the winter is. But there is nearly always a gap in annual production – the 'hungry gap' between April and June, when overwintering annuals have been harvested but newly sown crops are not yet ready.
Cropping of perennial vegetables is more evenly distributed over the year. Perhaps the most useful time for perennial vegetables is spring, as there are plenty of perennials in which the edible crop is the young shoots that emerge in April, May or even June – for example, Solomon's seals – from a perennial rootstock. There are also various perennial leaf vegetables that leaf out in the same period – for example, lime trees – which can begin to be harvested.
Other good reasons
You may well already have beds of perennials growing in your garden for ornament, for attracting bees or for fragrance. Why not have perennial beds with the same functions, but where the plants also have edible virtues? Some of the plants featured in this book, such as Solomon's seals and hostas, may already feature in your ornamental beds.
Perennial vegetables tend to be of more value to bees, other pollinating insects and beneficial insects in general; most are allowed to flower, whereas most annual vegetables are not. If you grow annual vegetables as well, you might well find that you get fewer pest problems on these because of the perennials nearby – you can even deliberately interplant annuals and perennials in various ways (see Chapter 2, page 26, for more on planting mixtures).CHAPTER 2
Growing perennial vegetables
In normal gardening lingo, 'perennial' is usually used to describe a low growing herbaceous or evergreen non-woody perennial plant. However, this book takes a much wider perspective. For example, trees and shrubs are also perennials, and in fact there are many nice edible leaves from them – lime leaves, saltbush leaves and mulberry leaves, to name but three.
Aquatic perennial plants are also included here, as are some bulbs, and one fern.
Types of perennial plant
This book describes plants of the following types.
A number of trees have edible parts that may be used as a vegetable, one example being the snowbell tree. A tree like this, which is grown for the young fruits, is not usually coppiced (see below) as this would cut off the fruiting wood.
Likewise, a number of shrubs provide vegetables. One is the American elder, whose flowers can be fried as a fine vegetable. I include bamboos – one of the finest of the spring vegetables – in shrubs, even though they are strictly speaking perennial grasses.
Trees that provide a leaf vegetable are often coppiced – cut off low down so they will produce vigorous new shoots the next year – to maintain them as more of a compact bush and so make leaf harvesting easier and more practical. The branchwood from coppicing may also be of use for firewood or for growing mushrooms on. The coppice cycle can be anything from one to five or more years, depending on the vigour of the tree and the desired size. I coppice large-leaved lime annually, and small-leaved lime every three to five years, and use the young leaves widely as a salad vegetable.
Herbaceous and evergreen perennials
Most of the plants described in these pages fall into this category, which gardeners often call simply 'perennials'. Herbaceous perennials – for example, asparagus – die down to underground roots, rhizomes or tubers in the winter. Evergreen perennials – for example, globe artichoke – retain some or all of their leaves over winter. Some perennials do not fit so neatly into these categories: for example, many mallows retain a rosette of green leaves over the winter in milder areas but may not do so in colder areas. From here on, herbaceous and evergreen perennials will be referred to as 'non-woody perennials'.
The alliums are good examples of perennial bulbs, and there are several described here. The top growth of bulbous plants usually dies back for a part of the year – though not necessarily winter. So, for example, Babington's leek dies back to a bulb from late July to early September, whereas ramsons dies back from late June to February. The bulbs that die back for part of the summer usually prefer well-drained sunny sites and can be particularly useful for a supply of leaves in winter.
Well, 'fern', actually – there is only one mentioned in this book, ostrich fern, whose young 'fiddleheads' are a well-known wild edible in North America and Scandinavia. Other ferns – for example, bracken – have been eaten in the past but are no longer considered safe to eat.
There are both climbing herbaceous perennials (e.g. hops) and climbing shrubs (e.g. grape vines) that can be used as vegetables. These plants can be grown in many ways, from bushy plants kept small by harvesting to climbers covering walls, fences, trees and so on.
These are plants growing in water, usually dying back to bulbs or rhizomes for the winter. An example is American arrowhead or duck potato, which forms tubers that can be cooked in various ways.
This term refers to plants that are perennial in warm climates and sometimes mild temperate climates, usually producing tubers or rhizomes, but are not hardy enough to survive winters in colder temperate climates. I have included some of these, even though they are not truly perennial in colder regions, because plants such as mashua and cinnamon vine, or Chinese yam, can be grown in milder temperate regions such as the south of England, and in warmer microclimates. Potato is a replant perennial (though the ones that evade harvesting often survive the winter and regrow), and runner beans can also be grown in this way.
Perennial root and tuber crops
It is common for folk to say to me, "It's all very well having all these leafy vegetables, but where are the substantial bulb and root vegetables to take the place of onions, carrots and parsnips?" Well, several of the above categories of vegetable have roots or tubers as the main crop. These are listed in the table, right.
You can grow edible perennials in any type of soil. Most soils can be improved, if necessary, by adding organic matter of whatever kind you can source. Loose mulches can help a lot too. A mulch is a material laid over the ground, either to clear weeds or to keep a planted area weed-free with minimal effort.
Beds can be pretty much whatever shape or size you like, and the planting design can be anything from a formal geometric arrangement to a much more random and semi-natural layout. Bear in mind the shade tolerance of the perennials you are growing (most prefer sun), and in general plant taller perennials towards the north side and/or shadier side, with shorter plants towards the south/lighter side.
It is really worth trying to make sure that the bed is free of perennial weeds before you plant out. In a smallish garden this may mean digging over the area, or alternatively you can use a sheet mulch (see opposite). Some of the perennial vegetables described in this book can be grown as a good ground-cover layer – so in effect they self-mulch – sometimes even under trees. See the table on page 31 for some examples of these.
A sheet mulch is a flat material (as opposed to, for example, compost or bark chippings) used over a whole area of soil, either to clear it for planting or to maintain a weed-free area when nothing else is growing there (for example, over winter). Sheet mulches are fairly quick and easy to lay but are not always aesthetically pleasing.
Various materials can be used for sheet mulching, including thick card, newspaper, carpet, black plastic, permeable woven plastic and biodegradeable mulch matting rolls made of flax, hemp, jute, etc. The plastic mulches are also available in rolls, which makes them quick and easy to lay. If using a roll of mulch when there are plants already in the ground to retain, you'll need to cut slits or holes in the mulch for them.
Using plastic mulches in the garden is a compromise in 'eco' terms, but they are very efficient and some can be reused again and again for many years. In a storm, large areas of sheet mulch can blow away if they start flapping wildly. To prevent this they should usually be weighed down with branches or prunings, or pinned down with pegs or 'staples' made of wire. If you don't like the look of plastic sheet mulches, you can cover them with a few centimetres' depth of loose chipped bark or similar organic material, though you will need to move the loose material once the sheet mulch has done its work in to lift the mulch material back up.
Most grasses, apart from couch grass, are killed after 3-4 months without light in the growing season, while 12 months is really needed to kill off dandelions, docks, couch grass and other pernicious weeds. Bindweed, horsetail and other nightmare weeds can take years to kill by mulching.
If your soil is not very fertile, you can put down fertility-building materials such as compost and animal manures beneath the sheet mulch.
There is often strong weed growth at the edge of the mulch where it meets existing grass. Plants in this situation exploit the fine soil conditions under the edges of the mulch to grow faster than normal, and you might find this growth needs cutting or strimming more often than other grass areas.
In mild temperate climates, as in most of the UK, planting of perennials is ideally done in autumn or winter, though spring planting is also possible. In recent years the climate in the UK seems to have been tending towards warm and very dry springs, and planting in autumn or winter means that you should not have to water plants during dry spring weather.
In colder climates, where the ground freezes for the whole of winter or is covered with snow for long periods, spring planting is more common, but if spring weather is hot and dry, extra watering is likely to be required.
After planting out, you can mulch the new plants with a loose mulch if you want. Many different loose organic materials can be used for this. The advantages are less weeding while the plants establish, and better soil conditions, especially in a dry first spring or summer; a loose mulch also provides a good habitat for beetles and other beneficial insects.
Disadvantages are the extra work involved, good conditions for slugs/snails and perhaps more expense. Whether it is worth it or not may depend on how quickly the plants will establish and whether they will form a weed-suppressing canopy of leaves.
If you decide to mulch newly planted perennials, plant first and put the mulch around the plants afterwards. Some materials – for example, leafmould (rotted leaves), garden compost or rotted farmyard manure – are likely to have weed seeds in, while others – for example, chipped bark, grass mowings (applied thinly) and fallen autumn leaves – may be weed-seed-free.
When you plant out, the density of planting and planting pattern will affect how the plants grow – close planting may lead to more competition and to plants growing taller but narrower. It will also affect the maintenance required, as closer planting means that more of the soil surface is covered so there is less chance for weeds to become established (see Diagram 1).
Another advantage of closer spacing is that when plants are harvested, more of the ground cover is left intact (for example, if leaves or shoots are harvested from a number of plants in the patch). Keeping the ground covered with plant growth as far as possible is a priority for any kind of ecological agriculture, because this keeps the soil in best condition, which benefits everything that grows in it.
Excerpted from How to Grow Perennial Vegetables by Martin Crawford, Marion Smylie-Wild. Copyright © 2012 Martin Crawford. Excerpted by permission of Green Books Ltd.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
ContentsForeword by Hugh Fearnley-Whittingstall,
Part 1 An introduction to perennial vegetables,
1. Why grow perennial vegetables?,
2. Growing perennial vegetables,
3. Maintenance of perennial vegetables,
Part 2 Perennial vegetables A–Z,
Appendix: Common and Latin names,