Mulch plants for different nutrients

I'm looking for deep-rooted mulch plants to bring up magnesium specifically, but im working on a larger list of other deep-rooted mulch plants too, and what nutrients they're rich in.

Zone 5/6 MI, clay soil, ample water, low elevation, sun areas and shade areas.

I've got comfrey and mullein already but I don't know what nutrients they're highest in

Here's a database of plant chemical constituents: https://phytochem.nal.usda.gov/phytochem/chemicals/show/11854?et=

I'm trying to get over my squeamishness about using the rash of LLM tools popularly called "AI" right now. So I decided to look at some old poorly-addressed questions at Permies and do my best to steer Copilot (powered by ChatGPT 4) toward valid data sources like the USDA.

Based on recent scientific analysis and USDA data, several plants have been identified as dynamic accumulators—plants that concentrate specific minerals in their tissues at levels significantly higher than average. For magnesium accumulation, the most promising candidates include:

🌿 Top Magnesium Accumulators (with Zone 5 and Clay Soil Suitability)
1. Redroot Amaranth (Amaranthus retroflexus)

Magnesium Accumulation: Known to concentrate high levels of magnesium and zinc.
Soil Suitability: Performs well in clay if soil is not overly compacted.
Zone: Hardy in USDA Zone 5.
Notes: In trials, it also showed high levels of aluminum, manganese, and sulfur. However, performance may vary depending on soil conditions. [Which Dyna...Garden ...]

2. Common Nettle (Urtica dioica)

Primary Accumulation: Calcium, but may also accumulate magnesium.
Soil Suitability: Thrives in clay and moist soils.
Zone: Hardy in Zone 5.
Notes: Proven to draw nutrients from subsoil, making it a true dynamic accumulator. [Which Dyna...Garden ...]

3. Russian Comfrey (Symphytum peregrinum)

Primary Accumulation: Potassium and possibly silicon; magnesium potential not confirmed but suspected.
Soil Suitability: Excellent for clay due to deep taproots.
Zone: Hardy in Zone 5.
Notes: Bocking 14 cultivar is recommended to prevent spreading. [Which Dyna...Garden ...]


🌱 Honorable Mentions (Potential Magnesium Accumulators)
These plants are often cited in permaculture circles but need more data:

Lambsquarters (Chenopodium album) – confirmed potassium accumulator, may also gather magnesium.
Dandelion (Taraxacum officinale) – deep taproots suggest potential for magnesium uptake.
Chicory (Cichorium intybus) – long taproots and clay tolerance.

As I was walking around here at our place, I noticed a lot of nettles growing lush in the cooler, wetter autumn weather.

My vegetable garden is in need of a nourishing layer of mulch, as I previously mulched with sawdust+horsemanure. I learned after mulching that  the sawdust consumes nitrogen as it decomposes, and that is showing in the yields... I've been adding extra nitrogen in the form of diluted urine before rain (or flushing with just water afterwards).

I used a good part of the afternoon pulling up nettles, tossing the plants with seeds on separate piles and the plants with no seeds (hopefully) on one big pile to wilt before using them as mulch in the vegetable garden. I hope a topping of nettle mulch will feed my vegetable garden, which currently is clay soil, compost and the said sawdust + horse manure and soon also chop and drop of the current crops.

Does anyone have experience with mulching with nettles? How did it go?

Yes, nettles will provide magnesium as well as other leafy greens such as spinach, kale, collard greens, mustard greens, and Swiss char.

Did you know that legumes are also rich in magnesium?

there are others though too many to name.