Rotating crops: 4 years or 4 crops?

Here is a basic question about which I am getting mixed answers. Is crop rotation counted in years or in the number of different plants which are grown in the immediate area? For example, if I plant tomatoes (nightshade family) this year, do I wait 4 years to replant or could I plant sooner if I can grow hairy vetch (legume family), radishes (mustard family), then spinach (goosefoot family)? If I use mowed and composted alfalfa, vetch or clover (legume family) as a mulch, does that count as one rotation after I take out the tomatoes for example? I could conceivably plant nightshades every summer if that last scenario were true. What am I missing?
If there is already a thread about this topic, please direct me. Thank you!

Hi Amy!

I think that in the grand scheme of things, the longer you can wait before you plant the same family of crop in the same place, the healthier your soil will be. I've seen crop rotation schedules anywhere from three crops to eleven crops.

Giving your plot a chance to lie fallow every so often is good practice too.

Adding compost and other natural amendments is advised any time you plant a crop. It's not just about crop rotation for the sake of pest resistance, but also because we need to add back the soil nutrients each crop draws out.

If you have enough land to go 4 years, that's sublime! If not, wait as long as you can and just add back good amendments each time you sow.

Others here might be able to lend more wisdom. I'd be interested to hear others' insights.

Same answer as all permaculture: IT DEPENDS.

For diverse soil biology, you want as close to a polyculture as you can manage, so a fast as the crops can cycle through the better. Four crops in one year would be great.

For disease and pest management, a long rotation breaks up the disease cycle so four years would be better.

We end up with a mix of systems depending on the goal.  The herb and kitchen gardens are polyculture and practically perennial with annuals planted back to the same spot (most self seeded) while the beds for canning and storage crops are rotated and treated like a traditional garden. Both are done for ease of harvest.  The first so we know where to find it quickly, the second so we can bulk harvest.  

This explains so much:

"For diverse soil biology, you want as close to a polyculture as you can manage, so a fast as the crops can cycle through the better. Four crops in one year would be great.
For disease and pest management, a long rotation breaks up the disease cycle so four years would be better. "
R Scott

Living in the high desert, I have four intensive garden areas that get enough low UV sun and water for nightshades. The rest of the acre is fruit trees with shady understory planting. The problem is, I would like to plant nightshades in all the intensive gardens during summer rather than just one. I could rotate potatoes, tomatoes, eggplant, chili but these are all nightshades. If I could reduce the rotation to two years, that would really help. Sounds like I'll be working on FAST CYCLING and switching the nightshade varieties in the cultivated beds. Thank you for this clarity.

It seems that the permaculture answer to this is to plant perennials.

Though promoting perennials this article says it is a 4-year plan.

common collection for us to consider now for a basic four-year rotation plan.

• Nightshades (Solanaceae): potatoes, tomatoes, peppers, eggplant

• Cruciferous (Brassicaceae): kale, cabbages, broccoli, cauliflower, mustard

• Legumes (Fabaceae): green beans, garden peas, snow peas, kidney beans, lentils

• Roots (Amaryllidaceae): onions, leeks, garlic, (Apiaceae): beets, parsnips, celery, carrots and (Chenapodiaceae): beets

https://www.permaculturenews.org/2016/11/18/rotate-annual-crops/


Bonnie Plants offers an easy plan using 4 crops that are rotated every planting:

One approach to crop rotation is to divide your plants into these four basic groups: legumes, root crops, fruit crops, and leaf crops. Imagine your garden separated into four areas, as shown in the chart at the top of the page. Each successive year, you would move each group one spot clockwise. So, for example, you would plant your legumes in Area 1 one year, then the next year you’d move them to Area 2 while the leaf crops from Area 4 moved into now-vacant Area 1—and so on.

https://bonnieplants.com/the-bonnie-blog/crop-rotation-made-easy/

It makes sense to me that different plants use different nutrients so rotating plants every year seems logical.

Years. the rotation times are built on how long troublesome diseases or pests can survive in the soil, what is growing there in those intervening years isn't important* Rotation is also to stop a build up of certain diseases that cannot easily be removed once they reach a high enough density to be an issue, some of them like club root can survive 15-20 years without a host plant, potato scab survives indefinitely. Others are shorter lived, black leg of potatoes survives only on a host plant or leftover potato halums/volunteers, late blight comes with the wind and can't really be avoided. Other pests like wireworms last 3-5 years not growing a host plant in that time frame will resolve the issue.

*some plants can help control certain pests, mustard when grown in huge dense beds can help control nematodes and wireworms.

Considering how long some pests/diseases can hang around, I think it depends on how strong your plants are to ignore those pressures. Each plant takes certain nutrients out of the soil, and might also add something else back to the soil. So I would plan a rotation so that between tomato plantings, you've also grown enough plants or added enough compost/amendments that the next tomato crop has at least as many nutrients in the soil as the previous crop.

It sounds like Stacie Kim’s advice to “add back good amendments each time you sow” and Mark Brunnr's suggestions for strengthening plants by adding lost nutrients will solve the depleting nutrients problem for a single plant family (like the heavy feeding nightshades). So I could keep planting annuals if I harvest more mulch from perennials. I do have lots of composted alfalfa, clover and hairy vetch; all of these are self-seeding annuals. I also have lots of pod producing trees: would composting the perennial tree mulch constitute giving back nitrogen rich leguminous material to the annuals? Does this support what Anne Miller refers to as “promoting perennials”?

If I intercrop with companions and perennials, which I do, will that reduce the risk of pests that live in monoculture gardens, especially if I rotate varieties in the plant family (tomatoes, potatoes, chili, eggplant)? Sounds like this would be a good way to balance risk vs reward in limited space.