Fertilizer Information


As always, store all chemicals safely and away from children and animals; always read the instructions before use; do not inhale, use downwind.

We’re sure the following will not be news to most people, but we hope some find at least something useful. Please feel free to correct us if you find something missing or downright wrong.

Of course, you won’t have a pair of scales at the allotment to weigh out the various fertilizers, etc., so as a rough rule of thumb and depending on the size of your hand as well as the product (bonemeal and Growmore are given as examples of ‘smallish’ and ‘largish’ particles, respectively; all conversions are approximate):

                                               Large hand                            Small hand

Closed handful                     Bonemeal: 3½ oz (~90 g)        Bonemeal: 1½ oz (~40 g)

(fingers touching palm)           Growmore: 2½ oz (~65 g)        Growmore: 1¼ oz (~30 g)


Open handful                                                                     

(fingers and palm cupped)        Bonemeal: 5 oz (~130 g)         Bonemeal: 2½ oz (~65 g)

                                               Growmore: 4½ oz (~115 g)      Growmore: 2 oz (~50 g)


Plants need three major types of nutrients for good and healthy growth: major nutrients (fertilizers), intermediate nutrients and trace elements.

Major Nutrients

There are three main groups of nutrients: nitrogen (N); phosphorus (P); and potassium/potash (K). Some are inorganic (I) and some organic (O), generally:

• inorganics are quick-acting, providing plants with a boost when used as a top dressing

• organics are slow-acting, providing plants with a steady supply of food over a long period.

Every plant requires all three major plant foods, but at different proportions at various stages of growth. For example, a flowering/fruiting plant, including many veg. plants, requires during their:

early stage—some phosphate (P) to promote root growth

growth stage—a fertilizer high in nitrogen (N)

later stage—a fertilizer higher in potash (K) to ripen the plant and assist flowering/fruiting

Fertilizers are classed as:

•   straight—supplies only one major plant food, e.g. sulphate of potash

•   compound—supplies at least two major plant foods, e.g. bonemeal

•   balanced or general—supplies all three, but not necessarily all in the same proportions, e.g. Growmore and  blood, fish and bone

Liquid fertilizers are generally faster acting than solid ones.  Never allow solid fertilizers to come in contact with leaves, they may burn—wash off immediately. Too much fertilizer can result in lush, sappy growth and poor fruiting, so don’t overdo it.

major nutrients Needed for: Shortage leads to: Apply:
Nitrogen (N)


(high N, in order: sulphate of ammonia; hoof and horn; potato fertilizer; Growmore; blood, fish and bone)

• leaf and stem growth (e.g. brassicas, celery, courgettes, leeks, lettuces, onions, rhubarb, squashes and pumpkins)

• legumes (peas and beans) fix atmospheric N in their root nodules, which is why you should dig in their roots after harvest

• stunted growth

• small, pale green leaves

• weak stems

• brassicas turning yellow then orange

• small fruits and tubers

• as a base dressing before sowing or planting

• a top dressing in spring and summer with an N-rich fertilizer. Repeat if necessary as quick-acting N is rapidly leached by rain


Phosphates (P)


(high P, in order: bonemeal; superphosphate; Growmore; blood, fish and bone; potato fertilizer)

• young plants

• root vegetables (e.g. carrots, potatoes, swedes, etc.)

• fruit and seed crops

• stunted roots and stems

• small leaves with a purplish tinge

• low fruit yield

• brown spots may appear on leaves, or edges may turn brown

• fruits may have an acid taste

• as a base dressing, or top dress with a compound high K fertilizer


Potassium/Potash (K)

Flower and fruit-maker

(high K, in order: sulphate of potash; potato fertilizer; Growmore; blood, fish and bone)

• fruit (e.g.  raspberries, strawberries,  toms, sweetcorn)

• flowers

• potatoes

• building up starches and sugars

• edge of leaves turning yellow then brown

• low fruit yield

• low disease resistance

• stunted growth

• fruit drop

• as base or top dressing, or

• water with your own comfrey tea (see Manures below)



intermed. nutrients
Needed for: Shortage leads to: Apply:
Calcium (Ca) • plant to utilize and transport other nutrients

• fruit, flowers, veg.

• especially on acid and potash-rich soils

• similar effects to nitrogen shortage • lime (see under pH  and lime)
Magnesium (Mg)


• essential to formation of chlorophyll

• deficiency quite common, especially on sandy, peaty and potash-rich soils

• tomatoes and roses


• yellow or brown patches between veins of older leaves (chlorosis); sometimes looks like iron deficiency

• young leaves may fall

• a compound fertilizer containing Mg as a base dressing, or

• a proprietary plant tonic (or Epsom salts) if symptoms seen during the growing season

• Epsom salts ~3 oz/ gallon (20 g/L) + few drops of detergent (acts as wetting agent) foliar feed spray to cover plants. Do not overuse

Sulphur (S) • all plants need S for protein production and management in the plant; unlikely you’ll have to add • similar effects to nitrogen shortage • none needed if S-containing product used (e.g. Growmore, sulphates of …)


Trace Elements

Only needed in very small quantities, large amounts may damage plants. Humus and impurities in fertilizers and composts (including your own) generally supply enough trace elements; iron is probably the only one you may need to apply.

trace elements Needed for: Shortage leads to: Apply:
Iron (Fe)


• acid-loving plants, e.g. camellias, azaleas, etc., and raspberries

• more common in alkaline soils

• yellowing between veins of older leaves (chlorosis); sometimes looks like Mg deficiency • sequestrene, or

• proprietary plant tonic

Molybdenum (Mo) • brassicas

• helps in protein production necessary for good plant health

• narrow leaves • generally shouldn’t be a problem

• use proprietary tonic if needed

• seaweed meal (will provide all nutrients)

Boron (Bo) • root veg

• lack can cause ‘corkiness’ in fruit and veg.

• brown heart
Zinc (Zn) • fruit and veg.

• helps to activate enzymes necessary for good plant health

• dieback
Copper (Cu) • fruit and veg.

• helps to activate enzymes necessary for good plant health

• dieback

• brown spots on leaves



(N, P, K (%), nitrogen, phosphate, potassium/potash; I, inorganic; O, organic; S, slow-acting; FQ, fairly quick-acting; Q, quick-acting)

NB: Halve the quantity of fertilizer when farmyard or compost has been dug in. Do not scatter fertilizers along a seed drill, may injure germinating seeds. Apply top-dressings along the sides of rows and lightly hoe in. In dry weather follow application of fertilizers with a good watering, cannot be taken up by plants until they are dissolved.  


Product N:P:K plus … Why? When? How much?
Bio plant food

(I, Q)

See package • Balanced feed for houseplants

• Can be used when potting on, but do not overfeed

Growing season As package instructions

(O; S)


plus Ca

• High in P for strong roots

• Great for root crops, e.g. carrots, etc., onions, dahlias and gladioli

• High in calcium

• Released slowly over 2–3 years

•  Autumn/early spring

• Rake into beds about 2 months before planting

• 4–6 oz/sq yd (120–180 g/m2) before planting fruit trees/bushes

• 4 oz/sq yd (120 g/m2) before sowing or planting veg

• Then to soil every 2 years

Fish, Blood and Bone

(O; S–FQ)

5:5:6 Good balanced general fertilizer • Every 4–6 wks from Feb to Oct

• Add to planting hole for trees/shrubs/bushes

• Use as top dressing over root area for established trees, etc.

• Add to  moist soil, or water well after application

 ~ 2¼ oz/sq yd (70 g/m2)

(I; Q)

7:7:7 Good general fertilizer suitable for all crops Spring–autumn

(see Blood, Fish and Bone)

1–4 oz/sq yd (30–120 g/m2)
Hoof and horn

(O; S–FQ)

11:0:0 • High in N

• Releases N gradually over the season, rather than leached by rain, can last up to 12 months in soil

• Good for all leafy plants

• Small amount of P for root growth

• Good compost activator

Autumn/early spring 2–4 oz/sq yd (60–120 g/m2) in Spring

1 oz/sq yd (30 g/m2) when transplanting seedlings, add 1 week before planting

Limes See pH and lime
Miracle-Gro food

(I; Q)

See box All-purpose soluble plant food for flowers, veg., fruit


Growing season As directed on the box



Product N:P:K plus … Why? When? How much?
Potato fertilizer

(I; Q)

6:10:10 Special formula for potatoes. Can also be used for other veg. crops At bottom of potato trench (under potatoes) 4 oz/sq yd (120 g/m2)
Sulphate of ammonia

(I; Q)

21:0:0 + sulphur • Basic source of N

• Increases soil acidity, so lime must be present, but do not use at same time

• Encourages leafy growth

• Use as top dressing for cabbages, etc.

• Good for adding to compost heap

Mar–Aug at 6-wk intervals ½–1 oz/sq yd (15–30 g/m2)
Sulphate of potash

(I; Q)

0:0:50 + sulphur • Basic source of K

• Helps provide resistance to disease & adverse conditions

• Fruit/flowers/potatoes

• Base/top dressing

• Stays in soil for 2–3 y

Growing season 1–2 oz/sq yd (30–60 g/m2) over rooting area of fruit trees, bushes, canes and along rows of plants that are in the ground for a long time
Super- phosphate

(I; Q)

0:18:0 • Basic source of P

• Strong root growth and healthy plants

• Remains in soil for few years

• Spring


• Rake in 2–4 oz/sq yd (60–120 g/m2)at sowing/ planting time


pH and LIME

pH is a measure of the acidity and alkalinity of the soil, on a scale of 1–14: pH 1 is very acidic and pH 14 very alkaline, with pH 7 being neutral.

It’s an easy matter to test the pH of your soil using a soil-testing kit, available from garden centres. But certain weeds can also indicate the acidity and alkalinity of your soil, e.g. creeping buttercup, sorrel, nettle, dock and mare’s tail show that your soil is becoming or is too acid.

Most vegetables prefer a neutral to slightly acidic soil (about pH 6.5–7.0).

However, certain plants prefer:

  • a very acidic soil (about pH 5.0), e.g. blueberries, camellias, azaleas, rhododendrons
  • a slightly acidic soil (about pH 5.5–6.5), e.g. fruit trees and bushes, raspberries, strawberries, potatoes, tomatoes, marrows, cucumbers
  • an alkaline soil (about pH 7.3), e.g. brassicas

(Ericaceous means acid-loving)

Lime—‘key to soil’

Lime is added to the soil to:

  • reduce soil acidity (i.e. increase the alkalinity)
  • provide calcium, an essential nutrient for all plants
  • encourage ‘good’ bacteria and earthworms
  • break up heavy clay
  • make other plant foods available; acts on humus, freeing up the nutrients needed for healthy growth
  • discourage pests (e.g. slugs, leatherjackets, eelworms)
  • discourage  diseases (e.g. clubroot)

But too much lime breaks down humus too quickly and plant leaves turn yellow because it results in iron being locked-up and unavailable to the plant.

The best time to add lime is after autumn digging, leaving it on the surface to be washed down by rain. Lime likes to be alone, so add manure, composts, fertilizers, seeds at least 2 months after liming.

Follow liming with brassicas; do not lime soil to be used for potatoes.

From 2011, the shed will stock both hydrated lime and dolomite lime. Hydrated lime is quick-acting. Dolomite lime, which also contains magnesium, is slower-acting.

570 g/m2 (~19 oz/sq yd) will raise the pH by approx. 0.5 units. If you suspect an acid soil but you are not sure to what degree, adopt a cautious approach to liming: 2–4 oz (60–120 g/m2) annually.


  Amount of lime needed to raise pH from 5.5 to 6.5 (i.e. 1 unit)
Soil type oz/sq yd g/m2
Sandy 23 700
Light loam 27 800
Humus-rich 37 1100



Adding loads of manure year after year will lower soil pH (i.e. make it more acid) and reduce soil fertility so that nutrients become ‘locked up’ and unavailable to plants; this why you should lime.


Product N:P:K Why? When? How much?
*Chicken manure pellets

(O; S–Q)

4:3:2 • Good general fertilizer, concentrated so use sparingly

• Also contains organic matter and trace elements, making it an excellent choice for top dressing

During growing season, as:

• base dressing, use at high rate

• top dressing, use at low rate

2–8 oz/sq yd (60–240 g/m2)
*Gro-Organic manure


  • Concentrated fertilizer

• Soil conditioner

• Produces healthy crops of flowers, fruit and veg.

• Breaks up clay soil

• Speeds up rate of composting

• Add to water to make liquid feed

• Add small quantity to multi-purpose compost for planting house plants

• Use when transplanting to encourage strong growth

• Sprinkle around base of flowers

Various, according to need For veg. and fruit:

4–5 oz/sq yd (120–150 g/m2)

Gro-well peat-based multi-purpose compost


  • Peat-based

• Use for potting on established flowers, fruit and veg.

(for peat-free compost see ‘Vital earth…’ below)

Year round
*Seaweed meal (O) ~1.5:0.2:3 • Brilliant as a tonic and conditioner, provides minerals, vitamins and trace elements

• As the organic components break down, they provide nutrients and increase the N content of the soil

• Improves soil structure and stability

• Alginic acid (the ‘gloopy’/ slimey stuff) in seaweed increases water retention so don’t have to water as often

• Carrot fly and blackfly don’t like seaweed products

• Good compost activator

In spring and autumn 2 oz/sq yd (70g/m2)



Product N:P:K Why? When? How much?
Vital earth peat-free multi-purpose compost   • Does not contain peat

• Added natural food and nutrients for up to 6 weeks

• For planting bedding, herbaceous plants, fruit shrubs and veg.

Comfrey and comfrey tea manures Approx.:


• Grows easily!

• Bees, etc. love the flowers

• Although low in N:P:K, tea allows nutrients to be immediately available to plants

• Compost activator

• First cut can be added in bottom of potato furrow

• Make tea:

(1) Wet method: add wilted or bruised comfrey to a barrel of water. Leave for 5–6 wks. Smells awful!

(2) Dry method: make a hole in the bottom of a lidded bucket/container. Stand it so that the hole is over a collecting vessel (e.g. large plastic milk bottle with top cut off). Fill the bucket with bruised/wilted comfrey and put a  heavy weight on the leaves. As the leaves decompose, a very concentrated liquid will then drip down into the milk bottle. Decant this liquid into small bottles and dilute for use. No smell! But it’s important that no water can get into the system

 Growing season • Strew wilted/ bruised leaves on soil to rot down and provide humus, etc.

• Tea use: dilute to the colour of weak tea

Compost heap—your own compost Approx:


• Best of all

• Adds humus to soil

• Improves soil by acting as a sponge to retain & release water

• Opens soil structure

• Provides a base for everything from bacteria to earthworms


• Can be added fresh in autumn (but not with lime), or

• Can be dug into topsoil in Spring (but not with lime)

• Generously, but be careful that soil does not become too acid

• Can be made into liquid food by suspending some in water (best in a sack tied at neck), dilute to the colour of straw for use throughout the growing season



Product N:P:K Why? When? How much?
Cow and horse manure Approx.:





• Horse manure better than cow manure

• Straw rots quicker than wood-shavings

NB: If you suspect that cow/horse manure could be contaminated with weedkiller, sow some cress seeds over it. Seedlings should be seen within a week; if no germination, suspect presence of weedkiller and do not use the manure for 12 months

See ‘Compost heap—yours See ‘Compost heap—yours
Green manure Depends on type of green manure (

e.g. field beans, grazing rye, trefoil (clover), mustard), but contains all nutrients you would expect to find in healthy plants

• Hold soil structure together

• Reduces nutrient leaching

• Leaf cover protects soil from compaction by rain

• Store nutrients in stems, roots and leaves, to be released back into soil

• Bean/pea (incl. sweet peas) roots have nitrogen-fixing  nodules on them, so dig in after harvest

• Whenever soil is left bare for a few months

• Field beans can be sown in autumn, overwinters well, then dig in during spring before flowering

• Broadcast the seed, then rake in

• Push beans in after broadcasting

• Dig in just before flowering

but: recently dug-in organic matter can inhibit seed germination —so if you’re going to sow seeds remove green manure to compost heap

do not use mustard as a green manure if clubroot’s on your plot, it’s a brassica


(O; S)

0.5:0.25:0.25 approx • Oak and beech leaves best

• Build into heap—6-inch layers of leaves between 1-inch layers of soil

• Leafmould is usually acidic

Composting is slow, leave for 12 months and use the following autumn/winter


1 bucket/sq yd —dig in or use as surface mulch
Mushroom compost/ manure (O) 0.5:0.25:0.5 • Useful for enriching sandy soil

• Contains lime, do not use around lime-haters

Year-round 1 bucket/sq yd —dig in or use as surface mulch
Spent hops

(O), (Q)

1:0.5:less than 0.25 • Useful peat substitute

• Adds humus

Let weather for a few months before use 1 bucket/sq yd —dig in or use as surface mulch
Wood ash

(O; Q)

Depends on type of wood burnt, but high in K (~5–10) and some P • Young wood best

• Keep ash dry

• Do not use on alkaline soil

Growing season 4–8 oz (120–240 g/m2)
Product N:P:K Why? When? How much?
Wool shoddy


10:less than 0.25:less than 0.25 • Releases N over period of years

• Now available commercially

• Also sold as mats to deter slugs

• Raw shoddy: autumn/winter

• Commercial: any time

• Raw shoddy: 1 bucket/sq yd —dig in or use as surface mulch

• Commercial: around plants

compost activators        
*Garotta and Activar Accelerates the composting process Throughout growing season Sprinkle a handful over each layer





• A very strong disinfectant, see bottle for instructions on use

• Has lots of uses; see website or ask in shed

Jeyes fluid

• Excellent disinfectant for greenhouses, paths, drains, tools, etc.

• Sterilizes the soil, so do not use if planting!

Insecticides, etc.

Cabbage collars

• Deter cabbage root fly

Dithane 945

• Not for sale after December 2010, but can be used until December 2011

• Protective fungicide to help control blackspot, downy mildew, tomato and potato blight, apple scab, leaf spot, peach leaf curl and rust

Tumble Bug

• Systemic insecticide for aphids, etc.

Slug killers

• Inorganic Blue pellets—a couple of pellets is quite enough around plants

• Organic—do not harm animals, pets and wildlife

Plant foods/tonics

• Bio plant food—general tonic

• Miracle-Gro—general liquid feed for use during the growing season

• Sequestrene—iron-containing tonic to combat chlorosis, e.g. in acid-loving plants (azaleas, etc.) and raspberries


• Available as fine- or medium-grade ‘granules’

• Sprinkle fine grade on top of seed and seedling trays/pots to prevent ‘damping off’

• Mix medium grade into composts to give a light, open compost for plants and when potting on


Feel free to download this jam packed PDF full of useful information about  Fertilizer 

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