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Seaweeds make great green fertilizers

Seaweeds make great green fertilizers

Green fertilizers are natural substances that can be added to the soil to increase its fertility. This includes manure, peat moss, seaweed extracts and bird and bat guano, as well as a variety of other substances.

Green fertilizers have lower concentrations of nutrients than chemical fertilizers, so they often give results that are less immediate and impressive. On the other hand, natural fertilizers have many advantages, such as:

  • They feed plants without being harsh, so it can be said that they are generally goof proof.
  • They are also not harsh to other forms of life present in your soil. This is important, since what actually makes your soil rich are all the organisms and micro-organisms that live within it.
  • They have a slower release rate, so they feed your plants more gradually and over a longer period of time, which is good in the long run.

Using green fertilizers

Most fertilizers are used to enhance the quality of the soil and thus feed your plants through their roots, but some can also feed your plants through their leaves. Solid green fertilizers can be mixed in with the soil or spread over it, while liquid fertilizers can be sprayed over the soil or on the plants.

Concentration is important. When planting a shrub, for instance, you should not mix in more than one third manure or peat moss with two thirds soil. Planting even an acid loving plant in pure peat moss is not a good idea. And when spreading solid fertilizers or spraying liquid fertilizers, always use the recommended quantity or concentration.

Choosing green fertilizers

Some green fertilizers, such as manure and organic fertilizer blends, may be used in most situations. But different fertilizers have different uses and characteristics. Below are a few examples.

  • Peat moss can be used to make soil more acidic, which is good if you want to grow plants like rhododendrons or blueberries, but bad for boxwood and spirea. In lawns, it may help moss grow, which is not good for the grass.
  • Corn gluten will help established plants grow, but prevent seeds and seedlings from developing. Since it dissolve slowly, you shouldn’t use it before or after over-seeding your lawn.

Some green fertilizers may be more suited to the spring, when plants are growing above the ground, while others may be better in the fall, when plants are growing roots and storing energy in those roots.

So when choosing a green fertilizer, consider the whole list of possible solutions and choose the one best suited to your needs.

Animal manure

Animal waste must be processed in order to be used in a fashion that is secure both for your plants and for the environment. The manure you buy in garden centers must have been processed according to approved animal manure management procedures.

Mulched organic matter

Grass clippings are a free source of nitrogen that can substantially reduce by one-third to one-half the fertilizer you’ll need to buy. Clippings also prolong the effects of any fertilization by returning nitrogen in an organic, slow-release form that promotes steady grass growth. (Colorado State University)

Mulched grass or leaves may be used as a green fertilizer on both your grass lawn and flower bed. But here are a few pointers on mulch:

  • You should follow the one-third rule: when mowing your lawn, do not remove more than one-third of the grass blades. Cutting more may slow root growth and cause thatching. Plus excessively long cuttings may smother your lawn and take a longer time to decay.
  • The organic matter should be well mulched.
    • Mowing your lawn when it is dry using a mulching lawn mower with a very sharp lawn mower blade will ensure the grass is well mulched.
    • If you want to use fallen leaves as well, wait for them to be as dry as possible. This way, when you mulch them, they will be reduced almost to dust and will decay much faster. You can do this with a  mulching lawn mower or a mulching machine. Note that if you use a lawn mower, you should not wait until the leaves are pilled up too high.

Also see how you can use mulch to retain moisture and fight weeds.

Knowing what your soil and plants need

Before you go ahead and add green fertilizers all over your yard or in your flower beds, it may be a good idea to bring a soil sample to your nursery and ask for a soil analysis. This will tell you exactly what is present in your soil and what it is lacking. Sometimes, adding more of something that is already there may do more harm than good.

But making your soil richer and more alive is rarely a bad idea (except in the case of plants which thrive in poor soils, of course). So using soil conditioners, manures and compost is rarely a bad idea.

And adding a little something to give plants a fighting edge when you put them in the ground is always a good idea. By the way, you should know about mycorrhizae. These are fungi that help plants grow roots faster (as documented on our page on helping plants grow).

Main ingredients

Most of the commercial fertilizers on the market today are known as NPK fertilizers, because their main ingredients are nitrogen (N), phosphate (P) and potassium (K). Fertilizer makers must specify the concentration of each one of these ingredients found in their products. A one hundred pound bag of 5-2-2 NPK fertilizer, for instance, would the equivalent of contain 5 pounds of nitrogen, 2 pounds of phosphate and 2 pounds of potassium. In Australia, the sulfur (S) content is also indicated. Other ingredients are present in all green fertilizers. Some of these may or may not appear on product labels.

The three main ingredients each have a different effect on plants:

N Nitrogen promotes leaf growth and health.
P Phosphate promotes root and shoot growth.
K Potassium promotes flowering, fruiting and hardiness.

Choose your fertilizer based on what you want to achieve. As a general fertilizer, choose one that has a high nitrogen index. For flowering and fruiting plants, choose one that has a higher potassium index. To promote root growth in the spring and fall, use one that has a higher potassium index.

Different green fertilizers for different needs

You usually use fertilizers to fix or improve something, be it to give new plants a better chance, to make your lawn and plants greener, or to help your plants make more flowers or fruits.

Different fertilizers can provide different benefits. Below are a few situations or problems along with the fertilizers that can help improve or fix them.

Note that this list is followed by another list that contains more information on each fertilizer. Before choosing a given fertilizer, check the second list to ensure that you made the right choice.

Good general fertilizer Bird guano, crab flakes (combined with seaweed), fish meal
Improve soil aeration and drainage Bat guano, granular gypsum
Make soil more alkaline (raise pH) Dolomitic lime, crab flakes
Activate composting Feather meal
Improve soil structure and quality Feather meal, granular basalt
Lighten hard soils Granular gypsum, horse manure, peat moss
General soil conditioner Horse manure, humic acid (mixed with fertilizers)
Improve root growth Bird guano, bone meal
Plant trees and shrubs Mycorrhizae, bird guano, bone meal
Sod lawns Mycorrhizae, bird guano, bone meal
Improve color and vigor Blood meal, poultry manure, seaweed (or kelp) extracts
Promote flower and fruit development Bat guano, bird guano, seaweed (or kelp) extracts
Improve root growth Bird guano, bone meal
Rose fertilizer Bone meal, horse manure
Bulb fertilizer Bone meal
Improve drought resistance Granular basalt
Improve soil aeration and drainage Bat guano, granular gypsum
Control fungi in lawns Bat guano
Control nematodes in lawns Bat guano
Control thatch in lawns Bat guano, feather meal
Control weeds in lawns Corn gluten
Control moss in lawns Dolomitic lime
Improve drought resistance Granular basalt
Fix salt or urine yellow spots on lawns Granular gypsum

Fertilizers and characteristics

Below is a list of green fertilizers along with their main characteristics.

bat guano Excellent green fertilizer. Recommended to promote fruit and flower development. Good soil conditioner. Improves soil drainage. Controls fungi and nematodes. Can speed up the decomposition process in the soil (may reduce thatch).
bird guano Excellent green fertilizer. Rich in phosphate (especially sea bird guano), calcium and other minerals. Promotes vigorous flowers, fruits, and vegetables, as well as root growth.
blood meal High in nitrogen (as opposed to bone meal, which is higher in phosphorus). Nitrogen, which is often lacking in soils and low in most fertilizers, helps plants keep a green and healthy look. Works as a compost activator.
bone meal High in phosphorus (as opposed to blood meal, which is higher in nitrogen). As a slow-release fertilizer, it promotes root growth over time (it must be mixed in with the soil when planting). Recommended for bulbs and roses.
calcitic lime Rich in calcium carbonate. Comparable to dolomitic lime. Raises the soil pH. This process may take several months, as the soil penetration rate is slow. The finer the powder and the better it is mixed in with the soil, the faster the pH will change. Good for plants that prefer alkaline soils, but bad for plants that thrive in acid soils. May be used to reduce moss growth in lawns.
corn gluten Rich in nitrogen, it is good for green leafy growth. As it is a fertilizer and germination inhibitor, it is used mostly for lawns. It prevents weeds from germinating, but it will also prevent grass seeds from germinating. Should not be used on freshly seeded or over-seeded lawns.
crab flakes Rich in nitrogen and phosphorous. Combined with seaweed extracts, it makes a complete fertilizer. Effective against nematodes.
dolomite lime Rich in calcium carbonate and magnesium. Comparable to calcitic lime. Raises the soil pH. This process may take several months, as the soil penetration rate is slow. The finer the powder and the better it is mixed in with the soil, the faster the pH will change. Good for plants that prefer alkaline soils, but bad for plants that thrive in acid soils. May be used to reduce moss growth in lawns.
feather meal Rich in nitrogen, it is good for green leafy growth. It activates compost decomposition and improves soil structure. Needs to be mixed in with the soil, so as to make the nitrogen available for the plants.
fish meal Rich in nitrogen (the hydrolyzed form is even richer), it is good for green leafy growth. Combined with seaweed extracts, it makes a complete fertilizer.
granular basalt Improves soil quality and makes lawns greener, more resistant to yellowing and droughts.
granular gypsum Loosens hard soils and improves aeration and drainage. Rich in calcium and sulfur. Can be used to fix salt and animal urine damage.
horse manure Not very rich in nitrogen, phosphate and potassium, this fertilizer can be used as a soil conditioner, especially to lighten heavier soils. It is typically used to grow roses.
humic acid Not a fertilizer as such, but rather a soil conditioner, humic acid increases the effectiveness of fertilizers. Mixed with fertilizers, it improves soil structure, nutrient intake and root development.
mycorrhizae Not a fertilizer as such, they are in fact microscopic fungi that live in a symbiotic relationship with your plants’ roots. The plants provide the fungi with the carbohydrates it needs, and the fungi help the plants absorb water and nutrients. The fungi must be in direct contact with the roots, so it must be used when plants are put into the ground or on the ground when putting sods into place.
peat moss Not very rich in nitrogen, phosphate and potassium, this fertilizer can be used as a soil conditioner, especially to lighten heavier soils and to help retain moisture and nutrients. It acidifies soils.
poultry manure Rich in nitrogen, it gives plants a green leafy growth. Typically low in potassium, it may be used along with a potassium rich fertilizer. May not be suited for plants that thrive in acid soils.
seaweed or kelp extracts Nitrogen and potassium rich, this fertilizer also contains a wide spectrum of plant nutrients. It promotes green leafy growth as well as vigorous flowers, fruits, and vegetables. In granular and water soluble form, it is approved for organic farming.

Homemade green fertilizers

For green fertilizers that are safe and sure to give your plants a boost, and that you can make at home, see the nettles and horsetail slurry recipes on our page on Green pesticides (yes, these slurries can be effective as pesticides and fertilizers).

Compost, although not a fertilizer as such, can be greatly beneficial to your lawn and plants. See our page on compost. Note that our site also contains general information on how to help plants grow, as well as information on green landscaping.

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