Seed Weed Fertilizer

Let me show you how we feed our seedlings using dilute seaweed extract to help keep them healthy and strong! It is gentle, sustainable, and effective. WHAT IS IT? Weed seeds = Elevator Screenings are what is left when grain is run through a seed cleaner. Clean grain goes into a bin and residues = screenings are disposed. Most grain elevators give weed seeds away free to any farmer willing to haul them. Some elevators charge nominal sums for screenings because…

How to Feed Seedlings with Seaweed Extract Fertilizer

If your new baby seedlings are a few weeks old now, it may be about time to feed them for the first time! In best practice, seeds are sowed in very mild, light, fluffy seedling starting soil mix, which is generally pretty devoid of nutrients. That is fine (for now) because tiny seedlings do not need or like fertilizer in the first couple weeks after sprouting. It can actually harm them, or “burn” the seed and prevent germination!

On the other hand, as they begin to grow, that fluffy seedling mix quickly becomes too light and won’t be nutritious enough to keep them happy for very long. Fertilizing seedlings with seaweed extract can help solve that! It is gentle, sustainable, and effective.

Let me show you how we fertilize our seedlings seaweed extract fertilizer to help keep them healthy and strong! It is very simple, and will make for a pretty quick post! At the end, you’ll find a demonstration video.

When do I start to fertilize my seedlings?

Seeds are pretty amazing little things. The seed itself contains all the food and nutrients that the little plant they produce needs for those first few weeks after sprouting. But as they start to mature, they’re also going to start to get hungry. Like any good baby should, they will get very cranky if you don’t feed them when they want it. Signs of distress include yellowing leaves, stunted growth, and even disease or death.

The best time to start fertilizing your seedlings is before they begin to get cranky. It is a lot better to keep them satiated then wait until they’re in trouble, and try to correct the damage. This is sort of a Goldilocks and The Three Bears kind of story. Not too early, not too late, not too much. We want “just right”.

Wait until after first couple sets of “true leaves” appear, and then start to feed them very lightly. About 3 to 4 weeks after germinating is a good target, about the time you’d want to start to thin them also.

What are true leaves? When a seed germinates, the first set of little leaves that emerge (often heart-shaped, and often looking exactly alike between dozens of varieties of veggies) are not the true leaves. These are the cotyledon leaves – their embryonic leaves. The two leaves that come after the cotyledon are their “true” leaves. Those leaves will more closely resemble what the mature leaves of the plant will look like.

These seedlings are TOO SMALL to be fed any fertilizer yet! The image in the top right show the heart-shaped cotyledon on a bunch of broccoli, bok choy, kale, and mustard greens. The lower right are tomato sprouts, and the on the left is a tomatillo. Wait another week or two, until the true leaves become larger and another set starts to appear.

If you’re going to plant your seedlings outside or pot them up within a few weeks after germination, it may not be completely necessary to feed them in their starting container. When they are planted outside in a bed of rich soil, or into a larger container with fresh soil and compost, they’re going to be essentially “fed” in that process. Yet if you are like us, and keep seedlings in containers for two or three months before planting them outside, they’ll definitely want a few rounds of food during that time.

What should I fertilize my seedlings with?

Many gardeners, us included, like to use a dilute organic seaweed extract fertilizer. It is nice and mild, making it very difficult to shock or harm your seedlings unless you really overdo it.

Seaweed extract helps the plants grow bigger and develop stronger root systems. Both of these contribute to overall improved plant health and immunity. Just like people, a plant with a strong immune system has a stronger ability to fight off disease, pests, or rebound from stress. Seaweed extract is loaded with over 70 beneficial vitamins, minerals, micronutrients, and enzymes! It contains magnesium, potassium, zinc, iron and nitrogen – to name just a few.

Cold-pressed kelp is commonly used to make seaweed extract. The harvest and cultivation of kelp is widely recognized as sustainable and environmentally-friendly! This is an excellent (and often overlooked) multi-purpose fertilizer; one that can be used for much more than seedling care! When we don’t have time to make a batch of compost tea, we water our garden beds or house plants with it too. Additionally, seaweed extract can be used to make foliar sprays. The plants can then absorb all that good stuff straight through their leaves.

See also  Hybrid Weed Seeds

Edit: We used to use this seaweed extract (at the time of writing this post), but the formula recently changed and it no longer says OMRI listed for organic gardening. I’m not sure what’s up, but we since switched to this organic seaweed extract instead.

From the book “Seaweed Sustainability” – Academic Press:

“Seaweeds grow in abundance in the oceans, many of which are edible and safe for human consumption. They have been documented to contain many of the essential nutrients such as omega-3 fatty acids, amino acids, vitamins, minerals, and bioactive compounds.

For many years, seaweeds have also been cultivated and utilized directly as food for humans or as feed to produce food for human consumption (e.g. fertilizer). Since seaweeds grow in many climatic conditions globally, their cultivation has minimal impact on the environment. Seaweeds are increasingly recognized as a sustainable food source with the potential to play a major role in providing food security worldwide.”

Kritika Mahadevan, Chapter 13 – Seaweeds: a sustainable food source

Kelp is such amazing stuff, that in addition to feeding it to our plants, we take some for ourselves too! No, not this liquid fertilizer… but in the form oral supplements. Algae is the only plant-based, vegan, or vegetarian source that contains all the most beneficial and essential forms of omega 3-fatty acids that are usually lacking in other plant sources. If you’re curious, read all about that here.

Another option people use for fertilizing seedlings is liquid fish emulsion. We don’t personally use this, so I won’t speak on its behalf.

How do I feed my seedlings seaweed extract?

Mix the seaweed extract with water according to the instructions on the bottle. If possible, use de-chlorinated water on seedlings. We use captured rainwater. If you allow chlorinated water to sit out, like in a bucket for example, the chlorine will dissipate in a day or two. If your city uses chloramines instead of chlorine to disinfect their water, it won’t burn off. When we can’t use our rain water, another option is to hook up this basic RV carbon filter to a hose – and that takes care of it.

Some types of seaweed extract have varying instructions for different types of plants or stages of growth. Look for instructions clearly intended for seedlings, or as a soil drench. We use about an ounce per one gallon of water, maybe just a touch over that sometimes.

Personally, I like to mix it inside this one-gallon watering can, especially for watering seedlings or working in the greenhouse. It is easier to handle than a larger 2 gallon can, and I really love the long, curved, skinnier spout. The design makes it very convenient for watering from below, as described next.

Wait a few days after the last time you watered, until the plants are getting a little thirsty and are due for another routine watering. Now, feed the seedlings the dilute seaweed extract mixture in place of their regular water. To accomplish this, we prefer to water from below.

Watering from below, into the trays. A note about our seedling trays: we prefer to use these heavy-duty seedling trays. They’re incredibly durable, will not crack, and can even hold bricks without bending! In addition to their longevity and strength, they’re perfect for watering from below. We still have some older flimsy 10×20 trays that aren’t totally “broken” and fairly functional, but this year I noticed most of them have developed little pinholes in the corners! This means all the liquid leaks out when practicing watering from below. And…. I figured this out the hard way, using a tray inside!

Feeding seedlings seaweed extract from below:

If you aren’t familiar with the concept of “watering from below”, it is exactly what it sounds like. It’s accomplished by pouring water (or in this case, seaweed solution) into the tray the seedling containers are sitting in. The soil will draw up moisture from the bottom, soaking up as much as it needs until the soil is evenly saturated.

Simply pour enough seaweed solution to evenly fill the bottom of the tray (with the containers still sitting inside of it) to about a half an inch deep. It is important that your trays are sitting level to ensure all the seedlings are getting a similar amount of seaweed solution. Otherwise, the liquid may pool on one side and leave the other thirsty.

After adding the seaweed solution to the tray, wait about an hour to see what happens. Did they already suck it all up, but seem a bit dry still? If so, you may need to add a little bit more. Alternatively, is the soil totally saturated, but a lot of liquid remains in the tray?

Allowing seedlings to sit in soggy conditions is not ideal. They breathe through their roots and do not want to drown. Therefore, we try to remove any leftover standing liquid from the trays within a few hours. Or, at least by the next day if we get busy. You can do this by either very gently tipping it out (if possible), or using a large garden syringe thing to suck it out. Yes… it is easiest if you don’t have a bunch of excess, so I suggest to go lighter at first and add more if needed.

See also  Weed Seed Prices

How often to feed seedlings seaweed extract?

You can generally feed seedlings seaweed extract every two to three weeks, depending on the brand. Again, read those instructions! After feeding, you should see an immediate boost in growth.


It is as simple as that. If you follow these steps to feed your seedlings, they will thank you and feed you right back!

Check out this video to see just how quick and easy it really is.

Do you need more seed starting and seedling care tips? Check out this post all about starting seeds indoors! Furthermore, here is another one that covers how to thin seedlings when the time is right.

In all, I hope you found this interesting and informative! Let me know if you have any questions.


WHAT IS IT? Weed seeds = Elevator Screenings are what is left when grain is run through a seed cleaner. Clean grain goes into a bin and residues = screenings are disposed. Most grain elevators give weed seeds away free to any farmer willing to haul them. Some elevators charge nominal sums for screenings because they can be fed to animals. For example, 10% to 15% weed seeds can be mixed into chicken feed.

HOW TO MAKE WEED SEED MEAL: Seeds of most plants make good fertilizer. The trick is to mill = grind seeds into a coarse meal or flour so they do not sprout. Most farmers use roller mills, hammer mills, or gristmills to grind weed seeds. If milling equipment is not available weed seeds can be baked in shallow (2 inch ~ 5 centimeter deep) pans at 350 degrees Fahrenheit ~ 176 degrees Centigrade for 1 hour to kill seeds. Baked weed seeds make very slow release organic fertilizer ideal for plants (like roses) sensitive to excess nitrogen.

If weed seeds are not available, substitute any type of waste or spoiled grain, for example, wet or dry brewer’s grains. There is no standard analysis for weed seed meal; nutrient content varies depending on species and proportion which change by locality and season. It is good practice to test weed seed samples yearly so fertilizer application rates can be adjusted as needed.

Below are some average nitrogen (N), phosphorous (P), and potassium (K) values for rough calculations. Note: lb = pound. 1 pound = 0.454 kilogram. 1 American ton = 2,000 pounds = 908 kilograms = 0.908 metric ton. 1 metric ton = 1 megagram = 1,000,000 grams = 1,000 kilograms = 2,200 pounds = 1.1 American tons.


BARLEY (spoiled, dry): 1.75% N : 0.75% P : 0.50% K = 35 lb N + 15 lb P + 10 lb K per ton (Manitoba 2011)

BEANS, SOUP (broken, dry): 4.0% N : 1.20% P : 1.30% K = 80 lb N + 24 lb P + 26 lb K per ton (New York 1988)

BREWER’S GRAINS (dry): 4.53% N : 0.47% P : 0.24% K = 90 lb N + 9 lb P + 4 lb K per ton (Pennsylvania 2012)

BREWER’S GRAINS (wet): 0.90% N : 0.50% P : 0.05% K = 18 lb N + 10 lb P + 1 lb K per ton (Pennsylvania 2012)

CANOLA SEED MEAL: 6% N : 2% P : 1% K = 120 lb N + 40 lb P + 20 lb K per ton (Saskatchewan 2014)

CASTOR BEANS (pressed): 5.5% N : 2.25 % P : 1.125% K = 110 lb N + 45 lb P + 22 lb K per ton (Egypt 2012)

COFFEE GROUNDS (dry): 2.0% N : 0.35% P : 0.52% K = 40 lb N + 7 lb P + 10 lb K per ton (Uganda 2015)

CORN, DENT (spoiled, dry): 1.65% N : 0.65% P : 0.40% K = 33 lb N + 13 lb P + 8 lb K per ton (Maryland 2014)

COTTON SEED (whole): 3.15% N : 1.25% P : 1.15% K = 63 lb N + 25 lb P + 23 lb K per ton (USDA 2015)

COTTON SEED (pressed): 4.51% N : 0.64% P : 1.25% K = 90 lb N + 12 lb P + 25 lb K per ton (USDA 2015)

COTTON SEED MEAL: 6.6% N: 1.67% P : 1.55% K = 132 lb N + 33 lb P + 31 lb K per ton (Egypt 2012)

COWPEAS (broken, dry): 3.10% N : 1.00% P : 1.20% K = 62 lb N + 20 lb P + 24 lb K per ton (California 2014)

FLAXSEED = LINSEED MEAL: 5.66% N : 0.87% P : 1.24% K = 113 lb N + 17 lb P + 24 lb K per ton (Manitoba 2008)

OATS (broken, dry): 2.00% N : 0.80% P : 0.60% K = 40 lb N + 16 lb P + 12 lb K per ton (New York 2010)

RICE BRAN: 4.00% N : 3.00% P : 1.00% K = 80 lb N + 60 lb P : 20 lb K per ton (India 2015)

RICE, BROWN (spoiled, dry): 1.0% N : 0.48% P : 0.32% K = 20 lb N + 9 lb P + 6 lb K per ton (California 2016)

RICE HULLS = HUSKS: 1.9% N : 0.48% P : 0.81% K = 38 lb N + 9 lb P + 16 lb K per ton (Philippines 2014)

RICE, WHITE (broken): 1% N : 0.21% P : 0.27% K = 20 lb N + 4 lb P + 5 lb K per ton (California 2016)

SOYBEAN MEAL: 7.0% N : 2.0% P : 0.0% K = 140 lb N + 40 lb P + 0 lb K per ton (Brazil 2011)

WEED SEED MEAL: 2.7% N : 0.90 % P : 0.90% K = 54 lb N + 18 lb P + 18 lb K per ton (Hungary 2013)

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WEED SEED MEAL: 3.02% N : 0.56% P : 0.77% K = 60 lb N + 11 lb P + 15 lb K per ton (Saskatchewan 2015)

WHEAT, HARD RED WINTER (broken): 2.00% N : 0.85% P :0.50% K = 40 lb N + 17 lb P + 10 lb K per ton (Kansas 2011)

For comparison, fresh dairy cow manure (86% water) contains 0.60% Nitrogen : 0.15% Phosphorous : 0.45% Potassium = 12 lb N + 3 lb P + 9 lb K per ton. Cow manure is the traditional standard against which all other organic fertilizers are measured.

For slow release fertilizer mill weed seeds into coarse flakes or meal. Grind weed seeds into powder for fast acting fertilizer.

WEED SEED MEAL APPLICATION RATES: Calculate application rates according to soil test recommendation for desired crop. Minimum application rate is 1 ton = 2,000 pounds per acre ~ 5 pounds or 1 gallon per 100 square feet ~ 2 Tablespoons or 2/3 ounce per square foot. Apply 1 pound of weed seed meal for every 25 feet of row or trench. Mix 1/2 to 1 cup of weed seed meal in each bushel (8 gallons) of potting soil.

Average density of weed seed meal = 0.3125 to 0.40 ounce per Tablespoon ~ 5 to 6.5 ounces per cup ~ 20 to 25.6 ounces per quart ~ 80 to 102.4 ounces per gallon ~ 5 pounds to 6 pounds 6.4 ounces per gallon ~ 40 to 51 pounds per bushel (8 gallons). 1 ton = 2,000 pounds weed seed meal = 40 to 50 bushels.

For example: 200 bushel per acre corn crop requires 200 pounds of nitrogen per acre. 200 pounds N divided by 54 pounds of nitrogen per ton of weed seed meal = 3.70 ~ 4 tons of weed seed meal needed per acre of corn. Weed seed meal can be tilled into the earth by conventional plowing, broadcast on soil surface, side banded down rows, or drilled into furrows or trenches.

For feeding earthworms broadcast weed seed meal (1 ton per acre or 2 Tablespoons per square foot) on soil surface. Reapply throughout the growing season when meal is no longer visible.


–> Weed seed meal is a natural = biological = organic fertilizer that requires decomposition before nutrients are available to plants. Bacteria, fungi and many other soil organisms eat weed seed meal then excrete nutrients in plant available forms. As soil organisms live and die, nutrients are constantly recycled = most fertilizer is tied up in the bodies of soil “critters” and is only available to plant roots in small amounts over extended time periods. Thus, weed seed meal is a slow release fertilizer that will not burn plant roots or leach from the soil.

–> Cold, wet soils delay weed seed meal decomposition. Warm, moist soils speed fertilizer availability. Early season crops may show signs of nitrogen deficiency (light green leaves) if soils are especially cold or poorly aerated = oxygen deficient. This is a temporary condition that will ordinarily correct itself in 2 or 3 weeks. Every 5 degree Fahrenheit temperature increase doubles microbial activity. As soils warm, nutrient cycling speeds up and more fertilizer is released for absorption by plant roots.

–> If crops must be seeded in cold soils, apply weed seed meal 2 to 3 weeks before planting so soil organisms have more time to decompose fertilizer and make nutrients available to plants.

–> Weed seed meal is an indirect fertilizer — it feeds soil organisms rather than plant roots. Large amounts of weed seed meal can be applied without crop damage or nutrient loss because the fertilizer is held by soil biology rather than soil chemistry. Thus, nutrients can be banked = stored for use by following crops. Weed seed meal has a “half-life” of several years. Nutrients are continually released in small amounts long after fertilizer is applied.

–> Weed seed meal works best on soils managed biologically. Chemically managed soils typically have smaller populations of soil organisms. Fewer “critters” slows nutrient cycling and restricts fertilizer absorption by plant roots.

–> To use LIVE weed seeds as fertilizer broadcast seeds into a standing cover crop like Red Clover (Trifolium pratense). Earthworms, ants, beetles and other critters eat the weed seeds. Clover kills any weeds that germinate. Caution: Do not try this unless you have a tall, aggressive cover crop that blankets the soil with dense shade.

RELATED PUBLICATIONS: Crop Rotation Primer; Biblical Agronomy; The Twelve Apostles; Managing Weeds as Cover Crops; Trash Farming; No-Till Hungarian Stock Squash; Planting Maize with Living Mulches; Living Mulches for Weed Control; Organic Herbicides; Pelleted Seed Primer; Crops Among the Weeds; Forage Maize for Soil Improvement; Forage Radish Primer; and Rototiller Primer.

WOULD YOU LIKE TO KNOW MORE? Contact the Author directly if you have any questions or need additional information on fertilizing soils with weed seed meal.

Please visit: — or — send your questions to: Eric Koperek, Editor, World Agriculture Solutions, 413 Cedar Drive, Moon Township, Pennsylvania, 15108 United States of America — or — send an e-mail to: Eric Koperek = [email protected]

ABOUT THE AUTHOR: Mr. Koperek is a plant breeder who farms in Pennsylvania during summer and Florida over winter. (Growing 2 generations yearly speeds development of new crop varieties).