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Frann Leach

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Organic Gardening:


Organic fertilizer facts


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Growing your own food the organic way produces food uncontaminated by pesticides and other nasty chemicals with a higher nutritional content. It also goes a long way to improving environmental diversity in your garden. But if you're using organic methods, you obviously need to use organic fertilizers which may be unfamiliar and difficult to find in your local garden supply store.

Before I go any further, let me clarify what I am talking about. I've seen sites online that talk about "fertilizer", but when you read them it's obvious that what the articles are really about is garden compost, a totally different thing.

Even the word compost can be confusing, as it refers to three different things:

You can make your own potting compost, of course, and you would most likely use some of your garden compost in it, but other ingredients are necessary for a good mixture, and if you want to use it for sowing seeds you would probably need to sieve it as well.

The situation is further confused because some manures like poultry or pigeon manure are so high in nutrients that they are often used in the same way as fertilizers, but not until they have been stacked for several months to cool down, as otherwise they are likely to kill your crops instead of encouraging them to grow.

But fertilizer is neither compost nor manure. Fertilizer is a feed almost always applied in handfuls rather than barrowloads. It's a lot more concentrated than anything you can produce in a typical compost pile, even if you wanted to.

Fertilizers are mainly used to provide the three main nutrients, nitrogen, phosphorus and potassium (or potash), usually abbreviated to NPK (K is for potassium - these are all the standard abbreviations used in chemistry).

There are basically two kinds of fertilizer, dry and wet. The dry kind is usually sprinkled round plants and then worked into the top few inches of soil, and the other kind (often called "tea") is diluted and applied with a watering can. A weak solution (usually half the regular strength) is used for foliar feeds, and a stronger one as a root drench.

Fish, blood and bone is a good general fertilizer, with a pretty good balance of nutrients for most crops.

Refer to the tables below, but basically, nitrogen is the main "energy source" (if we ignore sunlight). If you need a quick nitrogen boost, watering with a solution of dried blood should do the trick or for a more balanced mix, use liquid seaweed feed which has lots of trace minerals. At half strength this also makes a good foliar feed. Alternatively, hoof and horn can be worked into the soil around plants, but this is much slower acting.

Phosphorus is necessary for root development and by fruit and seed crops. It is also important for seed germination, though adding it to your soil won't make any difference to germination levels of the seeds you sow today. In most cases, there's no need to add phosphorus, but bone meal is a good source if you do need to, though it's quite slow acting. Bone flour, if available, will break down more quickly, making it available to your crops sooner.

Potassium is the main nutrient for promoting flower and fruit production. It also helps plants resist disease. Comfrey liquid is a good alternative to liquid tomato feed, as it's high in potash.

When referring to the tables, remember that even crops with a high requirement for a particular nutrient may well obtain this from your soil preparation. Fruiting crops like tomatoes, squash and sweet corn will probably need additional potash.

NB. Always wear gloves when using animal-derived products like bone meal, hoof and horn and fish, blood and bone.

Nitrogen requirements

Very high High Medium Low Very Low None
Celery
Onions (bulb)
Cabbage
Pumpkins
Corn (Sweet corn)
Cucumber
Onion (all)
Peppers (hot/sweet)
Squash (exc. pumpkins)
Asparagus
Carrots
NZ spinach
Parsnips
Pole (Runner) Beans
Spinach
Rutabagas (Swede)
Asparagus (established planting)
Broccoli
Radishes
Asparagus (New planting)
Mint
Parsley
Rhubarb (New planting)

Phosphorus requirements

Very high High Medium Low Very Low None
Celery
Onions (bulb)
Cabbage
Carrots
Parsnips
Pumpkins
Rutabagas (Swede)
Cucumber
Eggplant (Aubergine)
Lettuce
Squash (exc. pumpkins)
Tomatoes
Turnips
Watermelon
Beetroot
Broccoli
Brussels sprouts
Cauliflower
Endive
Garlic
Muskmelon (Melon)
Onions (green)
Peppers (hot/sweet)
Rhubarb (established planting) Spinach
Swiss chard
Asparagus (established planting)
Bush beans
Lima (Broad) beans
Peas
Potatoes
Radishes
Corn (Sweet corn)
Asparagus (New planting)
Mint
Parsley
Rhubarb (New planting)

Potash requirements

Very high High Medium Low Very Low None
Celery
Onions (bulb)
Cabbage
Carrots
Parsnips
Pumpkins
Rutabagas (Swede)
Cucumber
Eggplant
Lettuce
Squash
Tomatoes
Turnips
Watermelon
Beetroot
Broccoli
Brussels sprouts
Cauliflower
Corn (Sweet corn)
Endive
Garlic
Muskmelon (Melon)
Onions (green/bunching)
Peppers (hot/sweet)
Rhubarb (established planting)
Potatoes
Spinach
Swiss chard
Asparagus (established planting)
Lima (Broad) beans
Peas
Radishes
Snap beans
Asparagus (New planting)
Mint
Parsley
Rhubarb (New planting)


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Article ©2012 Frann Leach. All rights reserved.

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