How to wean your garden off its oil dependency- Step 1: Fertilizers

Happy New Calendar Year to everyone! I work in a school, so for me the year 'ends' in June and starts again in September... It also ends in the fall and starts again in the spring... It's an endless cycle of endings and beginnings, and odd spaces in between. This liminal time of the year is when I like to dream about my spring garden (and try to stay away from garden seed catalogues. Danger, Will Robinson!).

Growing your own veggies and herbs not only ensures that you have the best quality and highest nutrition, it can also reduce your impact on the environment. If you want to take that to the next level then you need to wean your garden off of its dependency on oil. The next level is barely a short step, and not hard at all to do.

Most commercial fertilizers are made from oil (natural gas in the case of nitrogen), or with the use of oil or coal in their production. In the end it's all the same chemicals (nitrogen, phosphorus and potassium), but where the chemicals come from, and what pollution is left behind in creating them, matters.

Nitrogen-

Some plants, like tomatoes, cabbage and corn, need more nitrogen than regular garden compost can provide. If your plants are low on nitrogen their lower leaves will be yellow-ish or the whole plant may be smaller than normal, as nitrogen is a major source for chlorophyll (the green stuff in leaves which converts sunlight into energy).

Cover crops-

One of the fancy and trendy ways to add nitrogen lately is to grow 'cover crops'. A cover crop is something that you plant, and then till back into the soil before it goes to seed. It makes sense in a large space like a market garden or field, but most home gardens just can't spare the space and time, especially in Canada where we have a shorter growing season. The most common cover crops are alfalfa, peas, oats, and buckwheat. It's definitely local, but more work than most people want to put in.

Manure-

Manure is a minor source of nitrogen, a fairly good one for phosphorus, and a good source of 'organic matter' (basically, dietary fibre for your soil).
Horse manure is easy to find, and the farmers may just let you haul it away for free. Other manures like chicken and pig aren't as easy to come by unless you raise them yourself, but they are much higher in nitrogen than horse manure. In fact, they're so high in nitrogen you can 'burn' your plants if you put it on directly. Better to run it through a composter first. Some other kinds of manure are cow, goat, and sheep.
Composted manure can be applied directly to your garden, raw manure needs to sit awhile in a composter and let the pathogens (bad bacteria, viruses and protozoa) either die or just simply go away. One year is a good length to let it sit and 'stew'. Try to keep your composter happy and healthy, and it will cook off anything that might hurt you. If you're concerned about it, let it sit for two years. (I would also suggest strongly against pig manure, as they carry some pathogens that are very harmful to humans.) All of these (except chicken and pig) will contain weed seeds, so you have no idea what you're direct-seeding into your garden. Not a pleasant surprise, guaranteed. So, compost, compost, compost.

Other good nitrogen sources are blood meal, fish meal, feather meal (from ground up chicken feathers- a very high source of nitrogen), and crab meal. If you prefer plant sources you can get alfalfa meal, soybean meal and cottonseed meal (the last two need to come from organic sources, as the pesticides used on the source plants can be very high). All of these are found at good garden centers (so probably not the pop-up ones which emerge at your grocery store every spring). They don't need to be composted, and can be applied to your garden as directed on the package.

Obviously, the most environmentally sensitive way to do it would be to find a source of local manure and compost it yourself. If you're really concerned about pathogens (or just don't have the space for multiple composters), buy your manure already composted. You can add it to your garden immediately or into your composter as a source of 'brown'. The nutrients can take a year or two to break down, so going through your composter won't hurt it at all. And in fact, it can help quite a bit.

And all of these sources are better than nitrogen sourced from natural gas.

Phosphorus-

Horse and cattle manure are a good all-round source of nutrients. If you really need to up the phosphorus content of your soil you can use rock phosphate. This mineral source lasts longer in the soil than the animal-sourced ones, however, it's only available to plants at a specific soil pH of 6 or 7 (neutral to slightly alkaline). If you don't know what this means just avoid this soil amendment. There's no point just chucking it in your garden and hoping for the best. I'll cover soil pH later if you don't feel like looking it up.
Chicken manure has a good supply of phosphorus, as does bone meal. Apparently bat guano from fruitbats is also good, but I've never seen it sold in stores. Maybe I haven't been looking hard enough.

I added bone meal to my front yard lawn to try and help it recover from the previous tenant's dog (huge patches of bare, burnt soil from the dog urine). The grass in the areas where I 'amended' the soil is dark green and somewhat jungly. I'd say it worked, and that pH is definitely fixed. It looks so different from the rest of the lawn I'm thinking I'd better even it out a bit this coming spring. But, if you do use bone meal make sure to wear a mask. You don't want to inhale that stuff.

Phosphorus helps plants to grow, develop, and establish good root systems.

Postassium-

When you're reading a fertilizer package, this is the 'K' in NPK (nitrogen, phosphorus, potassium). It's also known as potash.

Alfalfa meal is a good source of nitrogen and potassium. And then there's the old standby, manure. Sheep manure is better than other kinds for this. Some guides suggest a mineral called 'greensand', but it's something that is mined, so it requires a high input of oil to extract and transport it. If you have acidic soil (again with the pH talk), you can add wood ash as a good source of potassium. Don't add it to alkaline soils, though. If you're new to this it's probably safest to stick with alfalfa meal and manure. Those are my favourites.

Potassium helps plants resist disease and pests, stimulates growth, and helps with the transfer of water within the plant (amongst other things).

Liquid or dried kelp. Is it worth it?-

Sure, I guess. If you have the money. It's not necessary for a regular kitchen garden which you're just growing for yourself. It's not a magic bullet, obviously, and won't replace good care and watering, but if you feel like experimenting then go ahead. You can impress your mother-in-law with your garden prowess.
Kelp (a seaweed) stimulates the bacteria in your soil and provides additional nutrients that plants need in smaller quantities.

Further reading:

Nitrogen sources - from Rodale's Organic Life

Nutrient deficiency problem-solver - from Rodale's Organic Life

Why to compost manure - Ontario Ministry of Agriculture, Food, and Rural Affairs (it's a little technical in places, but very thorough)

More advanced topics/ for your interest and amusement:

BioChar - This is a somewhat advanced topic, and not something that I've bothered with. But, if you'd like to look into long-term soil improvement and carbon sequestration (ie. removing carbon from the atmosphere and locking it in the soil to help relieve the effects of global warming), then this might be of interest.

Pee on your garden - Yes, really. Your pee is a fantastic source of nitrogen.

Wikipedia article on fertilizer production