Garden Fertiliser Needs

Plants require many different nutrient elements for good growth and production, but nitrogen (N), phosphorus (P), and potassium (K) are the three major nutrients of concern to most gardeners. Plants also need small amounts of "trace elements" such as iron, magnesium, boron and manganese. Some fertilisers contain these as well although many occur naturally with Calcium (Ca) and Magnesium (Mg) supplied by limestone. The other required elements are obtained from air, water, and soil.

Every plant requires all three major plant foods, but at different stages of growth they are needed in different proportions. For example a flowering or fruiting plant, which includes many vegetable crops, requires some phosphate in the early stages, to promote root growth, followed by a fertiliser high in nitrogen for the growth stage and then one which is higher in potash to ripen the plant and assist in flowering and fruiting.

Nitrogen , N - for healthy stem and leaf growth;
Phosphate P2O5 - for healthy roots, strong stems and quality crops
Potassium (described as Potash, K2O) - for healthy leaves, flowers and fruit, also making plants winter-hardy and improving                   disease resistance.

Potassium helps to improve a plants' disease resistance, tolerance to water-stress, winter hardiness, tolerance to crop pests, and increased efficiency of (N) use.

The three Secondary Nutrients are:-

Magnesium (Mg++) required in small quantities for chlorophyll, also it is involved in the production of ATP, the molecule which facilitates energy transfer in living cells. Deficiency is manifested as white-ish stripes between the leaf veins. It is generally applied as soluble Magnesium Sulphate (Epsom salts) or in a more slow release form as Magnesium Carbonate (Dolomite Lime).

Calcium Ca taken up as (Ca++) ions is required for the healthy growth of new stems as it is used to give cell walls their strength. There is usually enough available in chalky soils and liming is the usual method of adding it, but this affects the pH of the soil. Too much can lead to Iron deficiency or chlorosis - which usually shows on younger foliage.

Sulphur (S) is taken up as Sulphate ions. It forms part of all proteins, activates enzymes and is involved in the flavour factors of many vegetables. Legumes have higher requirements for S than most other plants. Deficient plants are often uniformly yellow in appearance, stunted, thin-stemmed and spindly. It can be applied as soluble salts such as Potassium or Magnesium Sulphat.
Ammonium Sulphate can be used where an acidifying effect is desired.

Mixed fertilizers are normally sold by grade and contain two or three major plant nutrients. The numbers in the grade refer to the percent nitrogen (N), available phosphate (P2O5), and available potash (K2O). Proprietary fertiliser should display the N:P:K ratio. For example, if the N:P:K ratio is 7:7:7, as in Growmore, you know that the fertiliser contains equal proportions of the three major plant foods, and is, suitable for general use with all plants.

Some fertilizers like Osmocote, have been around for years and are trusted by most gardeners. Often the fertilizers are made for the specific type of plants like fruits, vegetables, evergreens, blooming plants and lawns just to name a few. These days there are many different types of fertilizers and it is easy to over-fertilize, therefore selecting the right type of fertilizer for your plants can be difficult.

Fertilisers can be either organic (derived from animal or plant remains) or inorganic (mined from the earth or man-made). Inorganic fertilisers are usually quicker acting. Fertilisers come in different forms, powder or granular for spreading on the soil and raking or hoeing-in and as liquids or soluble crystals for applying with the watering can.

How to use Fertilisers

The amount of fertilizer to apply depends on the natural fertility of the soil, amount of organic matter, type of fertilizer and the vegetables being grown. Get a soil test to determine your gardens' fertilizer needs. Based on the results of this analysis decide which fertilisers to apply before planting. The idea is to ensure that each crop has an adequate, but not excessive supply of the three major plant foods to begin with. Because many garden soils have been heavily fertilized for years, soil test results often indicate high levels of phosphorus and potassium which can stay in the soil for 2-3 years. In these cases, nitrogen is the only fertilizer recommended, since additional phosphorus and potassium are unnecessary.

Root vegetables such as carrots, swedes and turnips need plentiful phosphorus to develop well. While crop such as carrots, parsnips, potatoes, tomatoes and apples all need plenty of potassium to crop well.

Generally a balanced fertiliser such as Growmore or fish, blood and bone meets the needs of most soils. The exception would be if any bed already has a very high level of one of the plant foods, in which case choose fertilisers which do not contain this food because an excess of a particular element, does more harm than good.

Nitrogen is easily leached out of the soil by winter rain into deeper areas of the soil taking it out of the reach of the roots of shallow-rooted vegetables so is rarely in excess. Nitrogen fertilizer applied before or at planting time usually does not supply all the nitrogen needed during the growing season for heavy- and medium-feeding vegetables.

Either of the other two could build up. If potash is in excess, the answer is probably fish meal. If phosphate is in excess, the solution can be a combination of two straight fertilisers, like sulphate of ammonia and sulphate of potash.

Vegetables differ in their fertilizer requirements fertilisers for particular crops should be applied once the crop is growing, usually in liquid form,or easily soluble crystals. Some crops, like potatoes do alright with a balanced fertiliser, like Maxicrop all the time.

Onions and leeks are given high nitrogen fertiliser during the growing stage, nitro chalk or nitrate of soda and in the case of onions, one with a higher potash content later on to ripen the bulbs.

Leafy crops such as cabbages benefit with high nitrogen feeds all along. Beans get nitrogen from the air and do not require heavy nitrogen fertilization and are happy with Maxicrop while they are growing and then Phostrogen later on during the flowering and fruiting stage, because this contains more potash. Over-fertilizing these vegetables with nitrogen causes excessive growth of leaves at the expense of the fruit.
Straight fertilisers - Supply only one major plant food, Inorganic

Sulphate of Ammonia        [NPK 20-0-0 ]

A rapid acting nitrogen plant feed promoting healthy plant growth and rich green leaves. Supplies two vital nutrients for crop growth – nitrogen and sulphur. Sulphur lowers pH, and if you live in a high-rainfall area you do not want that. If you receive less than 20" of rain per year however, the sulphur may help improve your high-pH soil conditions.

Its nitrogen is not immediately available to plants because it must go through a chemical change. If your plants need an immediate shot of N you may be disappointed - especially in cold weather - because the change happens very slowly in cold weather. Conversely, in hot weather you may be happy with sulphate of ammonia because the nitrogen is more stable and does not volatilize so quickly, thus providing nutrition for a longer period.

Ammonium Nitrate       [NPK 34-0-0 ]

Only provides one nutrient - nitrogen. In places receiving more than 20" of annual rainfall additional sulphur from sulphate of ammonia is often not desirable, and therefore ammonium nitrate is the better solution Farmers love to use this type of fertilizer because it has very little effect on the PH level in the soil. Combines the stability of the ammonium form, with the immediate availability of the nitrate form to provide immediate nitrogen, even in cold weather with a much higher % of nitrogen than the sulphate form.

[Base dressing: 16 oz /sq yd for very acid soil, 8 oz /sq yd on vegetable plot. Compost heaps 8 oz /sq yd every 6 inches depth]

Nitro-chalk  [NPK 27-0-0 ]

Nitro-chalk contains ammonium nitrate mixed with  lime or chalk (calcium carbonate). Quick-acting, growth-promoting nitrogen fertilizer in granular form. Contains some lime so improves soil that is inclined to be Acid. Particularly good for brassicas and root vegetables. Avoid acid-loving plants. Use April to September.

Super phosphate  [NPK 0-17-0 ]

Encourages strong and healthy root growth. And rapid establishment of young or recently moved plants, Fruit, root and seed crops will produce higher yields and ripening will be improved.

Use all year round (top dressing particularly in spring). Best applied in autumn/winter for root crops is faster acting than bone meal and has a slightly acidic reaction on the soil. Use super phosphate around flowering plants in spring or early summer. Sprinkle it lightly around flowering shrubs and flowers once per year. Do not use too much as it can prevent uptake of other nutrients.

Nitrate of soda[NPK 16-0-0 ]

Nitrate of Soda provides a quick source of nitrogen to stimulate early spring growth, deep green colour, and stem and leaf growth.  Apply in early spring, after the last frost. Continue to apply every 6-8 weeks throughout the growing season. Often used as a source of nitrogen to plants in cold soils. The microbial activity needed to mineralize natural organic nitrogen (protein) is suppressed during those times of the year when the soil is cold.  It is short-lived in soil, so it is best applied just before planting time.

It is high in sodium so Nitrate of soda is not recommended in the low-rainfall regions  where salt build up is likely the soil is normally alkaline so may contain excess sodium or on plants that are sensitive to salt. The fertilizer increases both sodium and soil pH

Compound fertilisers - Supply at least two major plant foods.

Nitrate of Potash[NPK: 15:0:10.]

A useful 2 in 1 fertilizer supplying nitrogen as well as potash to early spring crops that would make too much soft growth if given nitrogen only. Apply direct to the soil as a top dressing 1-2oz per sq yard or mix 1 teaspoonful to 1 gallon of water and use two or three times during the growing season. Use Spring to early ~ summer.

Sulphate of Potash     [NPK 0-0-48 ]

Ideal for apple trees and other fruits. Potassium Sulphate or Sulphate of Potash (SOP) is a two-nutrient fertilizer containing 50% K2O equivalent, and 18% Sulphur, essential elements vital to many functions within the plant. Potassium Sulphate is a water-soluble, neutral salt, and has no effect on soil acidity or alkalinity (pH).

Quick acting fertiliser that helps to improve flower and fruit quality and is also beneficial to potatoes. Ideal for apple trees and other fruits.Provides greater strength and vigour in plants leading to improved resistance to weather and disease. Preferred for sensitive crops such as potatoes, tomatoes, peas, beans, ornamental plants, etc.

Scatter 35 gms per sq.m (1oz per sq yd) around plants without touching the plant stems. Some more greedy fruits such as raspberries, gooseberries and currents can be given up to 70 gms per sq m (2oz per sq yd). Lightly fork or hoe in. Repeat twice during growing season

Sandy and light soils will need top dressing more frequently i.e 3 or 4 times during growing season.

Sulphate of Iron

Sulphate of Iron is a plant tonic for ericaceous (lime hating) plants such as heathers, azaleas, rhododendrons and camellias. It can be used on any soil to correct iron deficiencies which cause leaf yellowing on roses and srubs as well a ericaceous plants. Take care; it will stain cloths, paving and other stonework. Uses only when needed; do not exceed the stated application rate.

Scatter 35g per sq m (1 oz per sq yrd) around the plants and lightly fork or hoe in. Repeat once or twice through the growing season. Apply evenly between the plants without touching the plant itself. Avoid using on windy days. Water well in after application.

Epsom Salts

Hydrated magnesium sulphate, used as a fast acting source of magnesium and sulphur. These are elements that are needed in the soil. Excellent organic fertilizer.

Organic Fertilisers

Bonemeal            [NPK: 1-13-0]

Organic, fine ground fertilizer that slowly releases a small amount of nitrogen and is an excellent source of slow release phosphate into the soil also contains calcium and some trace minerals; this encourages strong and healthy root growth. Because of its slow release it is a safe fertilizer especially when potting new or young plants. Perfect for bulbs and good for flowering transplant shock. Bonemeal can be used anywhere in the garden, as a base dressing (before planting/sowing) or a top dressing mainly in autumn and early spring.. It is often used when planting roses, trees and bushes as phosphorus is used by plants to promote strong and healthy root growth. The slow release aspect means the plant is well supplied for the crucial first year as it establishes.

Base dressing 4.5 oz /1sq yd. Top dressing 3 oz /sq yd.]

Fish, Blood and Bone [NPK: 6:6:6]

Organic based, fine ground fertilizer, containing bonemeal, dried blood and fishmeal, enriched with potash and other plant foods, excellent when a long term feed is required. Balanced feed, encouraging strong and healthy root and top growth. Use anywhere in the garden, from March to October - every six weeks.

Base dressing 4.5 oz /sq yd. Top dressing 3 oz/sq yd]

Dried Blood[NPK 12-1-1]

Dried blood is a very good source of nitrogen - around 12%. The organisms in the soil turn it into available nitrogen for plants were it is easily soluble and fast acting.  Lettuce and corn will benefit greatly. Can be used as top dressing or mixed with water and used as a liquid fertilizer. A slow release source of calcium and phosphorus. Is recommended for bulbs and most vegetables. Will aid the compost pile.

Hoof and Horn        [NPK: 12-0-0]

Hoof & horn is a straight fertiliser, like dried blood it is 12% nitrogen but it is slow acting. The benefit of this is that you can use it as a base dressing for leafy vegetables and other foliage plants like brassicas and it will gradually release its nitrogen payload over the season rather than in one go and then be leached by rain etc. If fine it can act fairly quickly in warm, moist soil but is generally long lasting.
Use spring to autumn.

Base dressing 4oz /sq yd. Top dressing 2oz /sq yd

Garden Lime

A safe form of lime to reduce soil acidity (raise pH). The activity and effect of beneficial soil micro organisms are enhanced by lime and most plant foods are made more readily available. Improves structure and drainage of heavy soils; improves speed and degree of decomposition in compost heaps. Supplies calcium; well-limed soil is less likely to carry clubroot disease.

Good for many vegetables, including beans, brassicas, carrots, lettuce and parsnips. Also good for shrubs, including buddleia, daphne, forsythias, broom, lilac. Bad for acid-loving species. Use all year round, but particularly in winter .

Calcified Seaweed.

This product is mineralised seaweed taken from the sea and is used directly on the soil to increase microbial activity. A saltwater plant, when ground, will stimulate root growth and has over 60 trace minerals needed by plants. This organic fertilizer when combined with fish emulsion will make a good all round fertilizer.

Chicken Manure Pellets              [NPK  4-2.5-2.3]

Widely available these usually have an NPK of 4-2.5-2.3 or thereabouts. Additionally they contain organic matter and trace elements, making them an excellent choice for top dressing.

Earthworm Castings

Organic fertilizer high in useful minerals and bacteria. The NPK is high and has over 60 trace minerals, almost an ideal additive to soil. Made by worms digesting organic matter and excreting the castings.
*Avoid chemical fertilisers which contain ammonium sulphate that is toxic to earthworms.

Coffee Grounds

People are finding that coffee grounds, usually thrown away are, rich in nitrogen and can be used in the garden and compost piles.

Garden Compost         Avg home made compost[NPK 0.5-0.27-0.81]

Garden compost made from leaves and fading stems tends to have relatively low levels of nutrients. Before a tree sheds its leaves it extracts useful nutrients (a process known as Senescence) and the organisms involved in the rotting process use up more of them. The main benefit of compost and leaf mould is adding organic matter high in micro organisms, humic acid, enzymes, vitamins, and humus which holds moisture, nutrients and improves drainage, by coating soil particles.

Groworganic (trade-name)

A concentrated 100% organic fertiliser which has been composed, processed and oven treated giving a safe, weed free, clean product which handles as easily as peat. Conditions soil/ breaks up clay soils. Promotes vigorous root growth systems on all plant crops.
Can be used safely on lime hating plants such as Rhododendrons and Azaleas.

Lawns   2-3 oz/ sq.yd
Seed Sowing 1 oz/ sq.yd
Potting   1 part to 25 parts peat/loam
Transplanting 4-5 oz / sq yd
Compost6 oz / sq yd between layers

Horse Manure           [NPK 0.7-0.3-0.6]

Horse manure contains fewer nutrients, but is bulky and therefore improves the texture and adds to the humus layer of soil. Usually dug in to soil in autumn and left over winter, or spread on to the surface of the soil and let worms do the work for you. Avoid manuring where you are going to have root veg, apparently makes them more likely to 'fork'. Manure is also slightly acidic, so loved by potatoes, loathed by brassicas.

Wilted comfrey leaves           [NPK 0.014-0.0059-0.034]

An excellent source of organic potash. Use them around soft fruit or when planting potatoes. Or add them to the compost heap at any time. Cultivated strains are available but don't despise the wild plant which grows beside ditches on many allotment sites.
Although the percentage NPK values are relatively low in comparison many fertilizers, in liquid form, nutrients are immediately available to the plants

Balanced or General fertilisers - Supply all three but not necessarily all in the same proportions with many also containing trace elements. These are mostly proprietary products

Growmore.       [NPK 7-7-7]

Equal parts N,P,K. Mainly for incorporating in the soil a week before planting Growmore is probably the most well known general
all-purpose fertiliser in the market, Growmore is a mineral based, regular sized granular fertiliser for easy spread and can be used on all types of flowers, fruit and vegetables during spring and summer with complete safety. Excellent for Brassicas. It can also be purchased in liquid form for application by watering.

Application Rate 4oz per yd dug in 2oz per sq yd top dressing

Chempak base fertilisers.

Mainly for making soil-less composts for seeds and cuttings or potting.

Phostrogen.         [NPK 14-10-27]

Soluble fertiliser high in potash. Good for flowers and fruiting plants like tomatoes.

Miracle Grow all purpose plant food                                          [NPK 24-8-16]

One of several new products on the market. They are liquid fertiliser's for general use.

Osmocote Controlled-Release Plant Food     [NPK 14-13-13]

Controlled-release plant food, releases nutrients for up to six months also contains magnesium and trace elements. As the soil warms Osmocote releases plant food .   

Maxicrop made from seaweed extract. For general use on established plants.
Maxicrop tomato. Formulated for tomatoes, but good for any flowering or fruiting crop

Lawn Weed and Feed + Mosskiller      [NPK: 8-0-3]

Greens the grass and kills most broad-leaved weeds and moss. Contains quick, intermediate and slow acting ingredients for steady growth. Apply 3 days after and 4 days before mowing on a still day when grass is dry but soil is moist. Do not use during drought or freezing conditions, or when rain is imminent. If no rain falls within 48 hours, water in with a hose or watering can.
Apply 2 oz / sq yd [70g per sq metre]

Spring and summer   [NPK: 11-5-5]

Spring and summer lawn fertilisers are high in nitrogen to promote quick growth. This very safe to use product is designed for all lawn types of all sizes. It will give your lawn that lush look. It is made as a minigrain for easy application by hand spreader.
Application rate 1oz sq yd 3 -5gms sq m

Autumn Lawn Food          [NPK: 3:10:5]

Autumn lawn fertilisers. Low in nitrogen, higher in phosphate (to strengthen roots) and potash. Promotes healthy root system to give a good start the following spring and increase root resistance during the summer. Apply when grass is dry but soil is moist.
Apply 1.5 oz / sq yd. Water in if no rain after 24 hours

Lawn Sand   [NPK 5-0-0] + Ferrous Sulphate

Lawn sand is made up from ferrous sulphate, ammonium sulphate and fine sand and commonly used to control many types of lawn weeds as well as control and prevent moss. When applied to the lawn the lawn sand 'settles' on the broad leaves and fibrous mass of moss and scorches them so they are destroyed. Because grass blades are fine with little horizontal surface area the lawn sand slides off and falls between the grass blades and onto the soil / thatch layer. This means that the grass blades are not scorched by the effects of the lawn sand.

Generally applied in spring or early summer it also acts as a first feed as when lawn sand reaches the soil it stimulates grass shoot growth and also helps to 'green' the lawn.

After applications do not cut the lawn for 3-4 days which allows the treatment can start to work. Avoid putting cuttings from the first mower cut on the compost contain higher than normal levels of chemicals

Rosefood    [NPK: 5:5:10] + magnesium and trace elements

Rose fertiliser's higher in potash than Growmore. Suitable for all flowering shrubs as well as roses
New plants: use 4 oz / sq yd as a base dressing. Containerised plants: 1oz with 2-3 hands full of moist peat in base of hole. Established beds: Mid March (at first sign of growth) 4 oz / sq yd, then 2 oz / sq yd monthly until August. Do not apply after this; it may encourage soft growth and fungal disease.

John Innes Base [NPK: 5:7:10]

Balanced general fertilizer. Mainly for making compost to the John Innes formula or used mainly as a base dressing before sowing/planting because the nitrogen is slow-released. Use spring to autumn.
Add 4 oz per 8 gallons for J.I. No. 1 or Base dressing 4 oz / sq yd

Q4 base.     [NPK 5.3-7.5-10]

Vitax Q4 is a general purpose fertiliser for use on a wide range of crops. It contains vital plant foods and trace elements essential for vigorous plant growth, abundant flowering and ripening of fruit. Also for making potting compost. Rather expensive for use outside in the garden.

Usage 140g to 200g per square metre.

Potato fertiliser[NPK 7-5-12]

Potatoes are an extremely productive and greedy crop. They require an exact feeding regime depending on the variety grown as well as the amount of nutrients already in the ground for them. As well as nitrogen to form foliage potatoes need a high level of potash for the tubers.

For first early potatoes the addition of extra fertiliser is probably unnecessary, assuming manure was added in the autumn. If it has not been manured previously, adding 200g/m2 of Growmore or fish, blood and bone will provide enough to get a decent crop.

Second early and maincrop potatoes will certainly benefit from additional feeding prior to planting even if previously manured and again at the point where the tubers begin to form. This is effectively when the foliage canopy between the plants begins to touch. The late maincrop varieties are in the ground longest and these need the most feeding. Adding additional nitrogen around ten to twelve weeks after planting should carry them through.

Chrysanthemum Food[NPK: 5-4-11 + 2Mg]

Balanced fertiliser specifically formulated for growing Chrysanthemums

Prepare the soil for growing beds by forking in 70g/ sq.m. After approximately three weeks repeat the above application and top dress around the plants, forking in generally then repeat every three weeks until cropping is finished.

Garden Fertilisers