If my main goal of gardening is to grow food crops (mostly beans and potatoes), how should I find the right balance between pulling weeds and leaving them?
Excellent question!
Most food crops, besides brassicas, amaranth and a few other exceptions, want a more fungal soil than what most weeds want. Most species we commonly refer to as weeds are low successional plants. What does that mean? It means they are the first to come after disturbance...sometimes called pioneer or ruderal species. They thrive in a bacterial dominant soil. They prefer nitrate for a nitrogen source. The higher a plant is in succession the more fungal the soil, the greater the need for ammonium, not nitrate.
So weeds are indicators. Depending on the weed, it may be indicating compaction, poor drainage, mineral imbalances, toxins, and almost always a lack of biology (life!) in the soil. They come in to remediate, balance, mine unavailable nutrients, break compaction....
Cultivating biology or I like to say, promoting life, is the name of the game. If you are plagued by weeds, it is a sure indicator the soil needs more life-more fungi, more protozoa, more nematodes. The soil needs more structure-more aggregation, more pore space.
Finding the right balance of removing or leaving the weeds is dependent on understanding your context. I almost never recommend pulling. Pulling is a disturbance and if you are trying to improve soil health, minimal disturbance is a key principle. Pulling is reserved for those that spread by rhizomes, like Johnson grass or when its your choice of therapy
or the weed has a very thin stem (and cutting requires more energy). Most often, cutting to the ground is your best bet. If its a more competitive weed and sprouts back too quickly from a crown, you can go just below surface and cut main root. Leaving the root means not only less disturbance but potentially exudates continue to be released to feed the biology (though most weeds give up less energy in the form of exudates than higher successional plants. 10% vs 80%), or as the root senesces (dies) it becomes food for decomposers and then pathways for biology. This is on the way to getting more soil structure.
First recommendation is to ID the plant then research and consider: is it an annual or perennial and how does that effect management? is it beneficial in some way? Does that make it more tolerable? Can you manage it by mowing, not allowing it to go to seed? can you plant something to outcompete it (cover the soil), something that is a more cooperative soil builder; is it a dynamic accumulator? If yes, what? Are you low in that mineral? Can you add it and effectively tell the weed its job is done? Can you ferment that weed and help the system go through succession more quickly by returning it to the soil. Chop and drop is in the same principal but composting and fermentation requires less energy for the soil biology and plants to mineralize and only a little more energy from you. Is the weed some exotic invasive doing nothing except taking advantage of an opportunity because it is highly competitive? Those are the most difficult. Think Bermuda or bindweed. Im not sure about poison ivy but definitely a bear to deal with. Again, most all weeds respond to a more biologically active soil by going away.
Another recommendation is to have a change of attitude when in the garden. Lol, but true! I will quote Jay McCain, author of the excellent "When Weeds Talk"..."the attitude is not to "kill" the weed but to feed the microbes in the soil by placing the weeds where they can be digested by the soil life. Some think plants are effected by the emotions of the grower. As such it is important to maintain the proper attitude if the best is to be obtained from the plants. 'Kill' is not the best attitude."
This is a long winded answer to a question that deserves an even more longwinded discussion but I hope you find some insight to guide you.
