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What compost offers, when to apply and amounts needed

My second most-asked question is: ‘Do you spread compost in summer before second plantings?’ The answer is simple: there is no need.

(The most asked question is: ‘Do I need to dig before starting no dig?’ The answer is similar: there is no need, but with an exception or two.)

This lesson considers why decomposing organic matter on the surface works so well to feed plants, indirectly. Appreciating how this process works will give you a deeper understanding of how no dig works, and the value of organic matter as a mulch.

Three useful points

  1. Soil organisms are more active and numerous in undisturbed soil, therefore more able to help plant roots find food and moisture, as and when they need it. There is continual symbiosis, or ‘mutual back scratching’. In return for helping plants to grow, soil organisms receive ‘exudates’ of food for their own survival and breeding.
  2. Soil organisms eat and digest organic matter, with their excretions adding to soil fertility. Worm casts, for example, contain thousands of bacteria and enzymes, as well as nutrients. They are also colonised by fungal filaments, as discovered by JN Parle in 1962, at Rothamsted Research Station, UK. 1
  3. Compost holds nutrients in a stable, insoluble form, so they do not leach out and are available over a long period. One dressing of compost helps to unlock food when needed, for two or more plantings. It is indirect fertility, made available to plant roots through a biological process.
Eight second crops in September, plus tomatoes, aubergines and peppers (first crops)
Eight second-crops in September, plus tomatoes, aubergines and peppers (first crops) – no compost or any other feeds for nine months
6. After spinach in the spring, this is November carrots: 10.66kg from 50x150cm/20x60in. Sown in June with no feeds or extra compost.
After spinach in the spring, this is November – 10.66 kg (23.5 lb) of carrots from 50 × 150 cm (20 × 60 in), sown in June with no feeds or extra compost

How to define fertility?

J Arthur Bower is one of my heroes. He took on a holding at Wisbech, UK, in 1934, and became famous for selling organic flowers at a 40% price premium because they were of such high quality. J Arthur Bower is still used as a brand name on sacks of potting compost in the UK.

He wrote this for the Soil Association’s Mother Earth magazine in April 1957:

‘Soil fertility is a fascinating subject to discuss, as I have found in the many talks I give. But it is a very difficult thing to define. Here is an outline:

– Simple, standard, and constant despite weather vagaries

– Assuring permanent ‘field capacity’ for water, which implies good drainage plus a high capacity to absorb

– Soil can supply growing crops with their needs for warmth and nutrients according to age and size.

‘Let me enlarge upon the word – simple.

‘When I was a young man learning my profession, soil fertility was simple. The only tricks were products employed for giving a fillip to exhibition blooms, such as Epsom salts or nitrate of potash.

But in the last 50 years, complications have come thick and fast. The plant breeder has to work hard to keep pace with ravages wrought by the interference of the chemist, who has never really had a true picture of fertility.

‘The basic needs of plants are: (i) moisture, (ii) warmth, (iii) light. The question of nutrients is secondary to these; but it has been made the dominant one, and the most intricate of all. Why?’

Bower continues on this theme, explaining how chemistry and commerce have taken over farming, while soil structure and quality have become ignored. This was in the 1940s and 50s, and in his market garden he practiced no dig. However this was rarely discussed, and his reputation was based more visibly on growing organically.

Bower recounted to a friend how a cement lorry had once driven into his no dig field by mistake, and then driven out, leaving deep wheel marks in the wet soil. However, by the end of that day, all the soil had rebounded upwards. He could hardly see where the lorry had passed, illustrating the health of his soil.

19. First crop was Charlotte potatoes harvested by Finn in late July
The first crop was of Charlotte potatoes, harvested by Finn in late July
19a. Second plantings exactly four weeks after they went in the ground: pak choi, kale, kohlrabi
Second plantings exactly four weeks after they went in the ground – pak choi, kale and kohlrabi
20. Second crops mostly, Homeacres 2nd September 2017 and 9-10 months after adding any compost
2 September 2017 – mostly second crops, and nine to ten months after adding any compost

Autumnal abundance, without feeding in summer

All of my autumn photos show abundant growth from summer plantings, when nothing has been added to the soil since the previous year. We mostly spread the annual dressing of compost in late autumn to early winter.

Despite this, I often see it claimed that compost should be ‘either covered through winter with polythene, or spread in the spring just before planting, to ensure no leaching of nutrients’.

In my experience, which is now 38 years of spreading compost before Christmas, this is not true. Growth has always been phenomenal, and consistently good throughout every year following, on different soils.

I read claims that sandy soils ‘cannot hold the nutrients like heavier soils can’. Yet the Facebook photos from Karen Drexler in Lesson 4, whose beds are sand, suggest otherwise. She applies compost once a year, for two to three crops, and in a climate of heavy rainfall.

  • Claims about scientific studies showing nutrients leaching out of soil are almost all based on cultivated soil. This factor is not stated. The biology and structure have been harmed by cultivation and problems ensue, such as nutrient leaching.
  • The ‘scientific’ focus on movement of nutrients misses what would be a more complex and worthwhile study: the quality of soil.

Another aspect of second plantings in summer is whether you can follow with a vegetable of the same family, or even the same vegetable. My plantings suggest you can, as with these two photos of calabrese in 2016.

4. A spring planting of calabrese was in April and this is 21st June, then after harvest we cleared plants to the compost heap
21 June – calabrese from a spring planting in April; after the harvest we cleared plants to the compost heap
5. Calabrese second crop on 27th September same year after spring calabrese, in the same soil, no feeds or compost
27 September – we had planted calabrese in the same space in July, with no feeds or compost given for the second planting

In terms of nutrients, calabrese is called a ‘heavy feeder’. It grows fast and large. I did not give any more ‘food’, yet it found the necessaries thanks to biological activity in the soil.

For second plantings, this means you have options. My preference is to plant vegetables of a different family to the first, as we discussed in Lesson 6. Sometimes you may need to replant with a vegetable of the same family as the one that has just finished. This is possible!

Harvests from one bed, 1.5 × 5 m (5 ×16 ft), in 2019

These harvest figures follow one application of compost in a year, from the no dig bed of my trial. In mid-March 2019, we filled the bed with new plantings (details in Lesson 4).

Through May, June and July these gave 44.02 kg (97 lb) of edible roots, fruits and leaves. This figure is after trimming and grading – it’s kitchen-ready produce.

As soon as these harvests finish, we plant again in summer. Sometimes I overlap the first and second plantings. For example I sowed carrots between lettuce that were still cropping, celeriac between cabbage, and kale between carrots which we were still pulling.

6. May 27th: trial beds with first plantings and the no dig bed is on right, plants were fleeced in April
23 March 2019 – mostly ten days after transplanting; the carrots have been sown
6a. 20th September: all second plantings, no feeds or compost in 9 months
21 May 2019 – some harvests are already happening
6aa. No dig carrots (Nantes Milan) 10 ft row gave 6.37kg. Sown 4th June with second crop after 12kg lettuce leaves
28 August – the bed is full of new plantings made in summer; no compost has been added, and no feeds given

The second plantings gave food from August to November, and there was even a third planting of Florence fennel after the second planting of cucumber, which had followed the first planting of beetroot.

The second and third wave of harvests totalled 51.71 kg (114 lb), with no feeds or compost given in the second half of the year.

The year’s total was 107 kg (236 lb) of vegetables from this one bed of 7.5 m2  (81 ft2), after applying 4–5 cm (almost 2 in) of compost in the previous December. This bed had started with 20 cm (8 in) compost in 2012, then had 8 cm (3 in) in both 2013 and 2014, and 5 cm (2 in) in every December since, and also one small bucket of rockdust in 2016.

The seven applications of compost total 54 cm (21 in), yet the bed still contains the same 20 cm (8 in) depth of compost.

Comparing growth from different composts

In February 2013 we used three different mixes of compost (and some soil) to fill three beds, all adjacent in a line. We used the same wooden frame – measuring 1.2 x 2.4 m (4 x 8 ft) – as the template for each bed, filled to a depth of 15 cm (6 in).

After filling and then firming the compost with your feet, a frame like this can be lifted off to put on new ground for refilling. We again used feet to push the bed sides into a 45 degree slope.

The contents of each bed were as follows:

  • Bed 1– old cow manure, two years old and dark
  • Bed 2 – a bottom layer of 5 cm (2 in) soil, and old cow manure on top
  • Bed 3 – recently delivered green waste compost (still warm) from the local facility, who sieve it to 15 mm (0.6 in)

All three beds were planted with onion sets in early April.

Growth through the spring was similar between Beds 1 and 2, but noticeably different in Bed 3. Some onions in Bed 3 did not appear, a higher proportion went to seed, and bulbs were smaller at harvest in August. Beds 1 and 2 gave strong growth and large bulbs, with hardly any going to flower. I saw little difference between those two beds.

In June I found space between the onions to interplant multi-sown beetroot. It grew well in all three beds, with noticeably the largest beetroots in Bed 3.

7. Compost trial set up: bed 1 nearest and bed 3 furthest
The compost trial has been set up – Bed 1 is nearest, Bed 3 is furthest
8. Onion harvest in August gave 100% more on beds 1 & 2, but some beetroot planted in summer gave more on bed 3
The onion harvest in August gave 100% more on Beds 1 and 2, but some beetroot planted in the summer gave more on Bed 3
9. Two beds with different filling, divided in the middle: compost left & soil right, planted with oca, yacon and peas in each bed
Two beds with different fillings, divided in the middle – the compost filled bed is on the left, the soil filled bed is on the right; both beds have been planted with oca, yacon and peas

This all suggests that the green waste compost was too fresh when delivered to give good growth – until about June it was continuing to decompose. This made some of its nutrients unavailable, because they were being used for the decomposition of its woody fragments.

However, by summer (once the decomposition had mostly finished) growth was stronger in Bed 3, even more than in Beds 1 and 2.

This is why I now buy such compost in the summer, for use in the late autumn and winter. Plus you often get more for your money, because it’s drier and weighs less in summer.

  • This nutrient grabbing – by immature compost and woody mulches – occurs much less when roots are growing in soil beneath any thin woody layer on top. The difference, in my 2013 example, was how a whole bed was filled with immature compost.

Commercial fertilisers vs compost

Early in 2013 I was given some ‘Grochar’ to trial. It was charcoal, with added mychorizzal fungi, seaweed, worm casts and a nutrient blend. The label says it is 5-5-5 in terms of NPK, what a chemical gardener would call a balanced fertiliser, suitable for many types of plants.

Grochar is expensive to buy and advertised as an ‘organic biochar fertiliser’, with application rates much lower than one would use if it were compost, so we filled the sacks accordingly. The main fill of all three sacks was topsoil, from trenches made when building my greenhouse wall in January.

  • Sack 1 had wood ash, dried seaweed, basalt rockdust and some dust of volcanic lava – about one third of a bucket mixed with the soil
  • Sack 2 had 10% grochar mixed with the soil
  • Sack 3 had 30% homemade compost (8–10 months old) mixed with the soil

Rockdust is ground rock, not literally dust, of basalt/volcanic origin. It supplies trace elements, and often improves growth on problem soils. Best to search for a local supplier. If I lived near the sea, I would spread seaweed instead, as soil and plant food.

I planted Sungold tomato plants (sown in March) on 23 May, and they cropped from early July. I did not weigh the harvests, but the pictures give an idea of how those in Sack 3 grew most strongly, and with the highest harvest from the earliest date.

In late May I also I planted a Genovese basil and trailing lobelia in each sack, just to see! Sack 3’s basil grew the largest.

This was not a ‘scientific’ trial, but a conclusion was not difficult to find: that it is simplest, cheapest and most reliable to use compost as your source of fertility. I felt that the Grochar was oversold in terms of its capabilities.

Compost is much better value to buy than any fertiliser. It is so much more than fertiliser, and gives the extras (beyond NPK) to grow large and healthy plants. Moisture, structure, microbes and trace elements are all found in good compost.

10. Preparing fillings for a trial of soil amendments: wood ash, seaweed and rockdust, sack 1
Preparing fillings for a trial of soil amendments – the mix for Sack 1 was wood ash, seaweed and rockdust
11. Mix for sack 2 was soil and 10% of the expensive “Grochar”
The mix for Sack 2 was soil and 10% of the expensive ‘Grochar’
12. Mix for sack 3 was soil with 30% homemade compost 9 months old
The mix for Sack 3 was soil with 30% homemade compost (nine months old)
13. Sacks 1,2 and 3 are ready for planting one Sungold tomato plant in each
Sacks 1, 2 and 3 are ready for planting – one Sungold tomato plant in each
14. I planted the tomatoes mid May and this is 30th May: left to right minerals, Grochar, compost
30 May, after planting the tomatoes in mid-May – from left to right are minerals, Grochar then compost
15. Growth on 15th June
Growth on 15 June
18. On 17th July, the only ripe tomatoes are in sack 3
17 July – the only ripe tomatoes are in Sack 3
16. Growth by 26th August
Growth by 26 August

After a final pick from each sack in the trial on 5 September, I measured the width of the stems at three feet high, and weighed the bottom three feet of stem from each sack. Also shown in the table below are harvests six weeks later from Charlotte potatoes, planted on 5 September.

Grochar had also sent me some of their potting compost. I used it when filling a propagation tray at one end, and I filled the other end with my standard potting compost, from West Riding Organics. The bean photo below shows you what happened, with the Grochar nutrients running out quickly (or perhaps not readily available to the bean plants), while the seedling growth is variable – I am unsure why.

18. Same sowing in two composts: West Riding multipurpose left, Grochar right
The same sowing in two different composts – West Riding multi-purpose on the left, Grochar on the right
18a. Lettuce germination was variable in this Grochar potting compost
Lettuce germination was variable in this Grochar potting compost

Another look at fertility – glomalin

This substance was discovered as recently as 1996, by scientist Sara F. Wright, while she was working for the USA Agriculture Research Service. She discovered how to extract the sticky material glomalin, which binds soil particles into aggregates, giving structure and tilth. She believes glomalin could account for a quarter or more of soil carbon, and exists for decades in undisturbed soil.

Glomalin is probably produced by mycorrhizal fungi, as Sara describes:

‘We’ve seen glomalin on the outside of the hyphae, and we believe this is how the hyphae seal themselves so they can carry water and nutrients. It may also be what gives them the rigidity they need to span the air spaces between soil particles.’ 2

During plant growth – as roots extend further into soil – fungi close to the original roots die off at the same time as new fungi colonise, and work with the developing root extensions. The decaying fungi shed their glomalin, and it remains in soil as a glue-like sheath around nearby particles.

This raises the intriguing point that all plant growth helps to build soil organic matter, as long as soil remains undisturbed.

‘In a 4-year study at the Henry A. Wallace Beltsville Agricultural Research Center (Maryland), Wright found that glomalin levels rose each year after no-till was started, with no plowing. Soil was protected from erosion by keeping fields covered with crop residue.’ 2

‘Glomalin went from 1.3 milligrams per gram of soil (mg/g) after the first year, to 1.7 mg/g after the third. A nearby field that was plowed and planted each year had only 0.7 mg/g. In comparison, the soil under a 15-year-old buffer strip of grass had 2.7 mg/g.’ 2

40. Soil fungi made visible after a leek harvest in winter
Soil fungi made visible, after a leek harvest in winter
41. Drills for sowing in June. Watering the drills highlights the fungi
Drills for sowing in June – watering the drills highlights the fungi

Compost and fungi

New knowledge about glomalin ties in with older work by Albert Howard in the 1920s, on the value of compost. He developed methods to make high quality, aerobic compost at the Indore Research Station in India. Next he discovered how just a small application of such compost could transform the soil of tea plantations, enabling plants to rediscover lost vigour.

Howard trained as a chemist, and had initially thought of compost in terms of chemical constituents, or a content of nutrients. At that time he assumed the composting process was about recycling and efficient use of waste organic matter.

On that basis alone he saw the potential of composting for Indian small farmers, who already had the ingredients to hand. He subsequently discovered that the compost they made actually increased the amount of total nitrogen, compared to each heap’s ingredients.

The results from using Indore compost, coupled with Howard’s knowledge – that nutrient levels had barely increased because he was adding so few – helped him to see compost as a game changer in many ways. He championed the role of soil fungi, even though they were little understood at the time, and he clarified the ability of compost to help fungi multiply.

During this same time (in the 1930s), mycorrhizal fungi were first being noticed and appreciated by scientists such as Dr Rayner. She worked for the Forestry Commission, on Wareham Heath in Dorset. Her obituary in the Empire Forestry Review June 1949 describes the huge impact of her research. This extract illustrates how scientific findings of great value get lost in a world of commercial applications:

‘There can be few countries in Europe and few states in the USA and Canada from which foresters have not visited Wareham. The correspondence regarding mycorrhizal relationships has been world-wide, embracing tea, coffee, rubber, oil palm and so on, as well as timber trees and herbaceous crops.’ 4

Since that was written, over 70 years ago, mycorrhizal fungi have been overlooked in mainstream farming, until recently.

Which brings us back to the value of transforming manure and other wastes into compost. I notice at Homeacres how crops grow better where the compost applied is ripe – dark, crumbly and with a sweet smell; not the ammonia or sulphur smells of manure stacked in an airless state.

There is much to discover about the relative benefits of different age composts.

41a. Fruiting bodies of Homeacres lovely soil fungi
Fruiting bodies of Homeacres’ lovely soil fungi
42. December harvest of oca reveals the soil fungi
A December harvest of oca reveals the soil fungi

More on second cropping vegetables, without feeding – which vegetables grow best in which half of the year

Here are more stories of first and second plantings, with no summer feeding of any kind. The photos also give an idea of which vegetables grow best in each half of the year, for example:

  • Potatoes yield most highly from spring planting, and suffer less blight than in late summer and autumn.
  • Brassicas grow most healthily in late summer and autumn, when there are fewer of their pests, and they are less inclined to flower.

In the Three Strip Trial we harvest second early potatoes in midsummer, then plant leeks for autumn harvests (see Lesson 5). Yields in 2019, from an area of 1.2 × 7 m (4 × 23 ft), were 48.2 kg (106 lb) of potatoes, and 25.41 kg (56 lb) of leeks, all from one application of 5 cm (2 in) compost, applied during the previous December.

Peas and broad beans, then chicories, then the annual mulch

Peas and broad beans grow most strongly in the spring, making leaf and stem before their flowering season of early summer. Therefore, to have a maximum of flowers and pods, it makes sense to sow them as early as possible (even in November for broad/fava beans), if winter temperatures stay above approximately -10°C (14°F).

Chicory and endive flower in the early summer, so are best sown after mid-June, for cropping in autumn. We had a fantastic harvest of radicchio from these plantings of 26 July (sown on 7 July), when the module-raised plants were three weeks old.

21. Mid June: first plantings include tall peas on left and onions next to them: peas suffer less damage from mildew and pea moth in June, compared to July and August
Mid-June – first plantings include tall peas on the left, and onions next to them; peas suffer less damage from mildew and pea moth in June, compared to in July and August
21a. Closeup of the tall peas Alderman on 15th June: in 2018 they cropped for only two weeks because of heat, at least they had mostly grown in the cooler spring
A close-up of the tall peas Alderman on 15 June – in 2018 they cropped for only two weeks because of heat; at least they had done most of their growing in the cooler spring
21aa. Chicory after the peas & onions, 91 days from sowing, was planted in dry heat 26th July. We watered the plants every two days in their first week
Chicory, following peas and onions – 91 days from sowing, and planted in dry heat on 26 July; we watered the plants every two days in their first week

The sequel to autumn harvests is clearing all debris, including (in this case) the plant stems, which otherwise grow again. Leave all the small roots in place, rake the beds level, then spread 3–5 cm (1–2 in) of compost, and you can relax while knowing that your soil organisms are fed and protected for the coming year.

On the paths we spread about 3 cm (1 in) of wood chip, from a pile which had been delivered in April. The wood was partly decomposed, with larger pieces still woody.

21b. Chicory beds after we harvested two thirds of the hearts in late November, and after we pulled the six weeds
Late November – chicory beds after we had harvested two thirds of the hearts, and pulled the six weeds
22. I rake the beds level after another harvest of all but two chicories, and we twisted out the main stems
Raking the beds level after another harvest of all but two of the chicories; we twisted out the main stems
23. Finally we mulched the beds with homemade compost of 10 months age, and the paths with old wood chips
Finally we mulched the beds with ten-month-old homemade compost, and the paths with old wood chips

Polytunnel plantings, two crops from one application of compost in May

My timing of compost application is different undercover to outside, for practical reasons and not to do with plant growth. There are two times during the year when the space is clear: after summer crops finish in early October, and after winter vegetables finish in April/early May.

I like to spread compost before the summer plantings because:

  • We have more time to spread compost in May than in October: in autumn the days are short and there is so much harvesting to do, as well as the new plantings of salads for winter.
  • The beds’ surface is a little lumpy for a while after spreading compost – an easier surface for planting and growing tall summer crops, compared to ground-hugging salad plants such as lettuce, endive, mustards and chervil.
27. Ten days after the annual mulch of 6cm compost, recent plantings for summer harvests
Recent plantings for summer harvests – ten days after the annual mulch of 6 cm (2 in) of compost
27a. Same view on 24th July, no feeds given to anything, only the compost we spread in May
The same view on 24 July – no feeds were given to anything, only the compost we spread in May
27b. Same view in late March, salads planted October & no compost or feeds for 10 months
The same view in late March – the salads were planted in October, with no compost or feeds for ten months

Summary of maintaining fertility

Mulching once a year with high quality compost – and using the no dig method – makes it quick and straightforward to keep soil in top condition. All these benefits follow: great crops, healthy growth, steady drainage, good moisture retention and few weeds.

Timing is flexible, and occasionally you are spreading compost while plants are growing.

  • You can spread the annual dose of compost in autumn, while vegetables and flowers are still growing, as long as there is space between. For example, spread compost in any rows which are wide enough, as with the leeks below.
  • You can spread the annual mulch of compost under tall brassicas in autumn. The aim is to feed soil organisms rather than plants, but the plants will also benefit (from improved soil structure and drainage for example).
24. We mulched these leeks with compost of 9 month horse manure in December, while they are still growing
We mulched these leeks with compost of nine-month-old horse manure in December, while they were still growing
25. Something different, mulch of spent hops c.3% N when dry, I would not use this for new plantings
Something different – a mulch of spent hops, c.3% N when dry (I would not use this for new plantings)
26. Woodchip seven months old, suitable for paths or in small amounts in compost
Seven-month-old woodchip – suitable for paths, and small amounts can be added to compost

1 A Microbiological Study of Earthworm Casts –, 1 April 1963

2 USDA AgResearch Magazine, September 2002

3 Albert Howard, by Keith Addison, Journey to Forever –

4 Journal Article, THE IMPORTANCE OF THE MYCORRHIZAL HABIT: AN APPRECIATION OF DR. RAYNER’S WORK, D W Young, Empire Forestry Review, Vol. 28, No. 2, June 1949, pp. 162–165          

sow & propagate
Transplant - Size, time of year, Spacing, support
container growing
Prune and train plants/thin fruit
Harvest times and method
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