Suppressors & Dynamic Accumulators

This is the last in our series on “Plant Roles” which means that once you know these last pieces of the equation, you’ll have all the knowledge necessary to put together a complete plant guild in your garden!

Here are the other articles in the series (read in any order):

Nitrogen Fixers

Mulch, Biomass, Mulchers

Pollinator Plants & Repellers

Food Forests

Suppressors

Suppressors are plants that intentionally inhibit the growth of other plants. This sounds counter-productive, but it actually has some very important applications for a food system!

Suppressors are used to intentionally combat weeds and keep otherwise invasive species under control. This is crucial when you’re trying to maintain a more natural food system where you want to avoid herbicides.

The way suppressors work is by either shading out smaller plants to keep them from growing, or by putting natural compounds into the soil that inhibit weed growth (which is called “allelopathy”).

While these can be effective, you should exercise caution. The last thing you want to do is plant something that will become invasive or harm the plants you’re actually trying to grow!

Examples

Allelopathic Suppressors:

• Black Walnut

• Sunflower

• Rye

• Sorghum

• Mustards

Shade Cover Suppressors:

• Squash/pumpkin

• Sweet potato

• Sprawling bean varieties

Nutrient Competitor Suppressors:

• Lambsquarter

• Alfalfa

• Rhubarb

• Dandelion

• Clover

• Plantain leaf

My recommendation would be to first observe plants that are already filling this role ecologically at your site. Do one of these plants grow near you and still manage to avoid becoming invasive? Are any of them useful in some way? If not, which can you easily remove if it proves to have invasive tendencies?

Dynamic Accumulators

Also called “nutrient miners” or “nutrient cyclers” (I may use all of these terms interchangeably in this article), these are plants that typically have deep taproots that take nutrients from deep in the earth and bring them up to the surface via foliage.

These are one of the most important ways to start building healthy soil and increasing the organic matter on your land.

Dynamic accumulators are mimicking the function they have in the wild; soil is poor quality, nutrient miners are seeded, nutrients are brought to the top level of soil, organic matter decomposes, repeat. Over time this is what yields truly rich soil! When properly managed, these plants can be powerful tools for building soil quite fast in comparison to nature alone.

Not all dynamic accumulators are equal in terms of the nutrients they mine however. Your soil may only need one or two major nutrients or have an excess of one nutrient so using a certain plant may not actually remedy the problem.

With plant nutrients there are a few main (and many more minor) nutrients to know about: Nitrogen, Phosphorus, Potassium, Calcium (Ca) and trace minerals like iron, magnesium, or zinc.

Nitrogen (N) is responsible for leafy and vegetative growth and photosynthesis.

Potassium (K) handles flower and fruit growth and water uptake.

Phosphorus (P) is important for root development and seed formation as well as energy transfer between parts of the plant.

Calcium (Ca) strengthens the structure of the plant and improves disease resistance.

Magnesium (Mg) Is responsible for photosynthesis and nutrient absorption.

Iron (Fe) is responsible for chlorophyll production and oxygen transport within the plant.

Zinc (Zn) supports growth hormones, enzymes, and plant structure growth.

Sulfur (S) is for protein, enzyme, and vitamin production within the plant.

Examples

• Stinging Nettle (N, trace minerals)

• Comfrey (N, K)

• Alfalfa (N, K, Ca)

• Yarrow (K, Ca, Silica)

• Borage (K, Mg)

• Sunflower (K, P)

• Mullein (K, Mg)

• Chicory (P, Ca)

• Dock (P, Mg)

• Lambsquarter (P, Ca, trace minerals)

• Dandelion (K, Ca, Fe)

• Plantain leaf (Ca, S)

Soil Indicators

The nice thing is that the weeds that grow on your site already can tell you a lot about what kinds of nutrients may be lacking or are in excess. Here are some basic visual cues:

• Yellowing leaves and stunted growth = nitrogen deficiency

• Browning or yellowing leaf edges and bad flower/fruit production = low potassium

• Purple/dark discoloration on leaves = poor phosphorus levels

• Distorted or curled leaves, blossom end rot on fruits (such as tomatoes) = calcium deficiency

• Yellowing between leaf veins and leaf drop on mature leaves = magnesium deficiency

• Yellowing between leaf veins on young leaves = low iron

• Small distorted leaves and poor fruit sets or small fruits = low on zinc

Likewise what weeds grow in your soil can be great indicators as well:

• Lots of clover, vetch, or other legumes = low nitrogen (legumes are nitrogen fixing plants)

• Nettles, chickweed, or lambsquarters = excessive nitrogen, overfertilized

• Bindweed, plantain = poor phosphorus levels (often due to compaction)

• Lots of mustards or sorrels = low calcium availability, acidic soils

• Lots of dandelion, sorrel, pineapple weed = Highly acidic soil with either poor nutrient cycling or high organic matter breakdown

• Wild carrot, chicory = Alkaline soil

• Plantain, goosegrass, thistle, dandelion = Compact soil (deep rooted plants like these fix that issue over time)

• Lots of sorrel or poppy = sandy low nutrient soil, often with low water-holding capacity

• Lots of purslane = Highly disturbed yet compact soil, low nitrogen but high in potassium and phosphorus

I may have mentioned before that the soil in a place is one of the easiest things to change about the site. It’s nice to start with good soil of course, but don’t let poor soil quality deter you from a piece of land if you’re willing to build it up!

Lots of permaculture gardeners insist on having a mix of seeds (Which I’ll formally dub the “Master Seed Mix”) that includes various plants that can show indicators to you of what might be going on with the soil but also what kinds of things will grow on your land. Here’s the recommendation I’ve been given by others (still working on putting my mix together):

• Legumes

• Root Crops

• Self-seeding Flowers (Calendula, Cosmos, borage)

• Brassicas (Mustards, kale, collards, broccoli, brussels)

• Herbs

• Cucimaceous plants (cucumbers, melons, squash)

• Asteraceous plants (aster family, sunflowers etc)

Here’s the mix I’m going with:

All that to say, you now have a ton of knowledge I wish I’d started out with 6+ years ago! It would’ve made my work a lot easier from the start.

I know this is sort of a technical article that seems intimidating with lots of information, but I’d encourage you to just try something. You don’t need to get it perfect, and you’ll have to experiment but have fun with it!

Let me know in the comments what you plan to do differently this next year!

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