My friend Madelon Oostwoud has written a wonderful book about growing amazing edible perennials in small gardens. Now in its second print, Een Kleine Eetbare Tuin is an absolute treasure trove of gardening information, perfectly tailored to small urban gardens. Her book is published by the KNNV
and is widely available to purchase. I highly recommend it! Madelon has kindly sent me the following extract in English to help urban herb gardeners develop a meaningful relationship with their soil.
Knowing your Soil
Garden soil differs from region to region, district to district and sometimes from garden to garden, and even from one end of a big garden to the other. Top soil is built up from small particles of sand, silt and clay, depending on the deeper layers of the ground below. Changing a garden on barren sand into a garden with fat clay is obviously impossible. Gardeners today know that you have to choose plants that suit your ground, and not vice-versa. The mineral material defines the choice of plants. The plants influence the organic material, and together they influence the soil. Improving your soil is certainly possible but should not be confused with changing the soil. Soil improvement is to improve the structure of the soil in your garden. It can be done in different ways.
Know your soil
Every ground or soil is suitable for an edible garden but not every plant grows everywhere successfully. Also, one soil may be easier to work then another. But complaining about unworkable soil has everything to do with wrong assumptions made by the gardener and little to do with the soil being unsuitable, a pet subject of one of Holland’s best known gardeners Romke van de Kaa.
Soil quality is determined by the ratio between the different particles of mineral material. Sand has the coarsest grain, clay the finest and silt is located in between. A loamy soil has sand, clay and silt, and is clearly a mixed form.
Types of soils
The different soils in most of Europe are described in the Soil Atlas of Europe, an initiative of the European Soil Bureau. It consists of a large number of maps, with an introduction to soil that explains the role and importance of soil, how soil is created, how to identify the soil in your garden, the relationship between soil, agriculture, our cultural heritage, forests and as a source of raw materials. Soil mapping and classification are also explained together with an illustrative and informative guide to the major soil types of Europe. You can find the Soil Atlas of Europe online at the site of the European Commission. Search for http://globalsoilweek.org/
if you are looking for information on the soil in your region outside Europe.
Sandy soil is light in weight, often also in colour and it feels grainy and loose. Sand cannot hold much water, neither many nutrients. Sand warms towards summer and stays cool long after the frost is out of the ground. Because sand does not retain nutrients we usually call it poor soil. Not all plants can grow on sand but it is easy to work and easy to improve using organic material.
Clay is heavy and compact. It holds nutrients and water well. Clay that is low on organic material is heavy, impermeable and intractable. Roots therefore have a hard time growing in clay. Working clay is heavy, as the particles literally stick together. Clay soils tend to dry slowly and do not easily warm up. Dry clay is hard and brittle. It freezes easily, which does generally not harm your perennials. A mix between clay and loam is loamy clay.
Peat comprises very few mineral ingredients. Peat is compact organic material that consists of plant remains. It is dark coloured – often almost black. Peat is moist and mostly low in oxygen. If your garden has peat soil on the surface, you have the most difficult ground with which to create a garden. It is in fact quite acidic, sticky when wet and crumbly when dry. This is also a reason to not purchase commercial potting soil because it consists mainly of peat. There is no food in it and it does not have a good structure. The structure is sponge-like. You are likely to recognise remains of undigested plants and roots. Dry peat is very flammable and used to be used as fuel in stoves and heaters.
The soil in extremely dry regions is usually brackish because of its high salt content. You’ll probably see a white layer coating the surface of the soil, your plants are growing poorly, and they’re suffering from leaf tip burn, especially on young leaves. Saline soil can stall plant growth, impede germination, and cause difficulties in irrigation.
Loam has an equal amount of sand, silt and clay particles, as well as organic material. It has the positive qualities of clay and feels soft and smooth. It is light structured. Loam is not lumpy, very fertile, well-drained without letting all water through and so often proclaimed the ideal garden soil. A mix between sand and loam is called sand-loam or loamy sand.
Improving your soil
If your soil is clayey, it is rich in calcium and minerals, and most likely alkaline. Apply a thick layer of compost or mulch (leaves, woodchips, biological cacao shells, freshly mown grass, hay or a few layers of cardboard or newsprint pages). This will improve soil life, and improve the structure of the soil. It also ensures that the soil can better retain heat, which can be especially important in the winter. Compost and mulch keep evaporation and the growth of weeds at bay.
Ideally compost will contain a large amount of soil organisms: worms, beneficial nematodes, woodlice, centipedes, bacteria, etc. These organisms and the plant-remains in the compost get the soil going. Therefore homemade compost is best. Commercial compost (in bags at the garden centre) is admittedly organic in composition, but does not have any bacteria and fungi in itself. Once you opened the packaging you will not be able to detect one single worm. In homemade compost there are always all kinds of insects and worms. Once outside the composter, they will get to work for you to improve your soil. If there is virtually no organic life in your soil it can easily be started in no time with your own compost. Divide the mature compost from the bottom of your compost bin and simply distribute it in your garden. The easiest way to do it is with a soil sieve. Simply sieve the compost over your plants, and tip the particles that do not pass through the sieve back in the compost bin to further compost. Mature compost can be divided over the ground with a rake or by hand. If you have a worm tower (also see chapter : Compost) use the compost when it looks dark, and you do not ‘recognize’ anything any more. To separate worms and compost – briefly put the compost out in the light. Worms do not like light, and will crawl away into the deep. You can view the contents of (part of) your worm tower also by throwing out worms and all the plants. They will be just as happy in the top layer of your garden as in the worm tower or compost bin. If your worm tower has a tap for the worm tea, dilute it with water and poor it over soil and plants.
Improving acid soils
Sand and peat are usually acidic. Sand is acidic and additionally nutrient-poor soil. You could add some lime to ‘ease up’ the structure of the soil. Lime is alkaline, the opposite of acid. Lime thus de-acidifies acidic soil. But be careful with the addition of lime. In sandy soil lime connects the sand particles, in clayey soil usually only enough calcium is present and lime would just reduce the structure. Acid soil is therefore best improved by adding compost.
Just spread compost on your garden and soil and let nature take its course. By ‘feeding’ the soil, it becomes healthy. Healthy soil can hold enough water and all other elements by which plants grow. Healthy soil grows healthy plants that do not suffer from diseases and pests.
Mulching with leaves (dry, coarse, old and brown material) creates a low pH, where fungi and bacteria feel at home. That’s good for trees, woods and spices. Mushrooms can also find their way there.
Mulching with compost (wet, green, young material) creates a higher pH with more bacteria than fungi.
Another way to improve soil and structure of your ground is by planting green manures. Green manures are plants that ‘work’ the ground for you. They are almost always and everywhere successful.
Bare areas with new houses or vegetable gardens where the soil for a long time has been exhausted by monoculture, sowing green manure is an even better solution than applying compost. While the plants take root and grow, thousands of organisms underground start to give your soil a nutrient-boost. Even in winter, when the ground is bare and reflect on lies. In the coldest months, when your soil seems deep asleep and no the plants are yet stabbing their heads above ground level, the roots of green manure do a perfect job. They improve your soil simply by rooting, making ways for insects and small craetures, airing the soil with their burrows, feeding the soil with their feces.
Sow from spring to late September, work the seeds lightly with a rake and let the plants grow and do their job for you as long as you like. A mixture of natural plants works most effective and is additionally wonderful in your yet un-landscaped garden. You can leave the plants grow until after flowering, and even after being felled by frost. Over time you can mow them, leave them to ‘wither’ or rake them in.
Plants that you let ‘die’ and digest on the ground, such as alfalfa, mustard, winter rye, bring structure and humus in the soil. Real green manure! Legumes, such as clover and vetch, enrich the soil with nitrogen. Nitrogen is vital to plants and therefore to the success of your garden. Without sufficient nitrogen, plants will be unable to grow. Though nitrogen is abundant in the world, most of it is a gas and most plant cannot use nitrogen as a gas. They must rely on the addition of nitrogen to the soil in order to be able to use it. A few plants love nitrogen gas. They are able to draw the nitrogen gas from the air and store it in their roots. These are called nitrogen fixing plants. Besides being green manures they also fixate the nitrogen. Please note that each nitrogen-fixer is a green manure, but not every green manure is a nitrogen-fixer.
Examples of green manure
Below green manures are annuals. They did not return and will not proliferate. You can buy the seeds at any garden centre. Most are not suitable for consumption, so do not use them for it.
Buckwheat (Fagopyrum esculentum) Applicable to the poorest lands; Sowing: spring t / m summer. Growing rapidly and deeply rooted.
- Fenugreek (Trigonella foenum graecum) For heavy and light drained soil.
- Crimson clover (Trifolium incarnatum) Suitable for all grounds and nitrogen-fixer
- Lupine (Lupinus angustifolius) Especially on light, acid soils.
- Alfalfa or alfalfa (Medicago sativa) Applicable on dry ground; sowing: Summer, let stand until the following spring.
- Mustard (Sinapis alba) Apply to all grounds; sowing: March September.
- Phacelia (Phacelia tanacetifolia) Apply to all soils.
- Serra Delle (Ornithopus sativus) as green manure especially on sandy soils.
- Field beans (Vicia faba) to be applied on all grounds, seeding: September-October. Makes a perfect mulch after mowing.
- Vetch (Vicia sativa subsp. Sativa, Vicia villosa) Suitable for all grounds and nitrogen-fixer
- Winter rye (Secale cereale) Applicable on all grounds; sowing to November and leave until Spring.