How can we promote the longevity and productivity of our garden soil?
This Lesson Plan is part the Gardening Module of SustainEd Farms' virtual programming.
Background: Crop Sequences
The garden and farm are ever-changing places. Like the constant change that comes with the arrival and passing of the seasons, crops germinate, proceed through their lifecycle, and then die off, only to be replaced by a new generation of plants. When new plants replace those that die, they inherit the biological and chemical history of the land they now sit in, living on the residues of life in the past. In the natural world, this sequencing unfolds on the watch of the organisms that happen to live in a particular location (those that have evolved to live in a given environment). On the other hand, farmers and gardeners must facilitate these growing sequences within the constructed environments we create for feeding humanity. In other words, farmers and gardeners must harness (that is, understand, employ, and promote) the natural tendencies of living creatures in order to create sustainable production systems within ever-changing natural environments.
For years, conventional farming practices have resisted looking at nature as a template for growing food: they have attempted to grow the same crop, on the same land, year after year, with no other plants present (through use of herbicides), with no pests present (through the use of insecticides), with no cover crop, using heavy tillage, and applying environmentally degrading fertilizers. Such practices -- which will be looked at in greater depth in lessons to come -- have changed little with time, and are common systems for most agricultural producers in the United States. Yet, these “short-term gain” based schemes, which look very little like the sustained success of nature's guide, are now collapsing as a consequence of resisting the change that natural processes facilitate (natural succession). On those conventional farms, soils are becoming more degraded, food is becoming less nutritious, and yields have declined as pests and weeds build immunity to toxic chemicals. It turns out that the attempt to command nature (rather than harness it) ultimately leads to an unsustainable future.
For farmers that have recognized these facts -- that nature is a dynamic, changing process that cannot be held constant -- the most obvious management decision has been to create sequences of cropping plants (which is quite literally changing the type of plants that grow in a single location). To do this, growers have come to understand special properties among certain crops, and fit those understandings into a management plan that syncs with the timing of biological phenomena. Knowing how to select certain plants to grow at certain times, in certain locations, in particular arrangements, and under proper circumstances will allow the grower to carry out their operation indefinitely.
In this lesson, you will be using the DGSN garden template to design (or re-design) a garden space. Along with the questions and information provided below, you will use your knowledge of the crops grown in the past to mindfully develop your garden with a respect for natural change, thereby creating a crop sequence.
Learning Objectives
Students will be able to...
Identify reasons to grow different crops in different locations from season to season
Create an environmentally friendly garden design
Balance the needs and wants from the perspective of the grower while simultaneously working in harmony with nature
Academic Vocabulary
conventional farming /kənˈven(t)SH(ə)n(ə)l ˈfärmiNG/ noun. - a type of farming that relies heavily on high inputs (tilling, fertilizer use, irrigation frequency and magnitude, etc.) for a singular output (same crop year after year)
crop rotation /kräp rōˈtāSH(ə)n/ noun. - a farming technique that involves planting., in a fixed pattern, a certain type or species of plant after the first (different) type or species dies
crop sequence /kräp ˈsēkwəns/ noun. - a farming technique [similar to a crop rotation] that involves planting, with no fixed pattern, various types of plants after a certain plant type or species dies
Directions
1. Gather your materials. You will need the following supplies:
DGSN garden template (1) · pencil or pen · colored pencils, makers, crayons · printer (you may opt to design on your computer)
2. To begin your crop brainstorming process, you should review the information below on why it is logical to have a crop sequence:
Outcomes for plant health:
Nutrient balance: Soil is filled with varying levels of different nutrients depending on what was growing in the soil in the past, and different plants use different levels of nutrients. So, when crops are rotated properly, the soil is never fully depleted of a certain nutrient, making that nutrient available to the next plant. Like humans, who need many different nutrients, plants need a wide variety of minerals (nutrients) to grow. If plants are rotated, no mineral is depleted too much, which means that every type of plant should get access to its full spectrum of nutritional needs (thus increasing yields!).
Resilience to enemies: Crops that have balanced diets are especially robust. When crops have access to lots of nutrients, it helps build their eventual immunity to pests, weeds, and fungal/bacterial pathogens that destroy yields. Diseases affiliated with certain plants do not have as much time to proliferate under a system of crop sequencing, because the crop is moved or not grown in the next year or season. Sequencing and rotations disrupt the migratory patterns and availability of nutrients for natural enemies, making it difficult for the foe to establish a sustainable population.
Soil enhancing properties:
Curbing erosion: The introduction of different root structures from a variety of plants help build structure within soil. These units, called soil aggregates, form when roots (in conjunction with microorganisms) carve pathways for nutrient and water exchange in the soil. With added structure, soil particles are more likely to stay intact when they become wet, which helps control the rate of erosion.
Water retention: Soil with a variety of root structures has a higher content and diversity of pathways for water to percolate into.
Mineral availability: Both plants and soil need sufficient nutrient balances to be considered “healthy.” When soil is mined by a single plant type, minerals become unbalanced, and the life within the soil suffers. Sequencing crops limits this mining of the soil by ensuring there are “breaks” in the uptake rate of certain vital minerals.
Building economic durability:
Multiple revenue sources: You’ve probably heard the phrase “don’t put all of your eggs in one basket.” The idea of this saying is that relying on any single thing -- be it an idea, a person, a product, or a revenue generating crop -- is risky, because if it fails, there is no backup to mitigate the hardship of the failure. Increasing the variety of plants on a garden or farm can make the grower confident that they will succeed, even if one particular crop fails to grow well. Having a crop sequence ensures that there is no financial dependence on the production of a single crop.
Steady financial growth: The biological principles of crop sequencing are understood well enough to confirm that any practice that does not rotate its crops will all-too-certainly deplete the soil of the necessary ingredients for life. This will eventually make the soil unusable; for a farmer, unusable soil means no source of revenue. Therefore, the only way to have a continual operation is to abide by the supply and demand of the environment, which can be met by rotating crops effectively.
3. After reading about why it is important to develop a system with changing plant varieties, read on to discover common practices that are in use today for crop sequences:
Never plant the same crop after itself in the same location. In fact, it is best to not plant anything within the same family of the crop in question after a full season of growth. You can use the list of these botanical families to aid your crop sequencing decisions, but be wary: avoid sequences where a disease may span different but consecutively placed botanical families.
🥬Play to your vegetable’s strengths… Though the “strengths” of any crop don’t fall within the exact bounds of its botanical family, sorting them into these categories can give us a general functional overview of how the crop can be used for a particular purpose. Consider using the distinctions in the table below to guide your rotation choices:
Family | Examples | Functions within Agroecosystem |
Grasses | wheat, oats, rye, sudangrass, corn Did you know? … Cereals and grains account for a significant portion of the human diet worldwide. | → typically, these plants are rapid colonizers, ushering in a quick succession when competitors die (or are harvested) -- some are, therefore, useful cover crops because they can quickly invigorate soil biology at the end (or beginning) of a heavy feeding cycle → excellent forage for grazing animals, which recycle the plant material by digesting it and working into the ground (adding to organic soil carbon sink); can also be terminated through human intervention. |
Legumes | lentils, beans, peas, peanuts, clover, soybeans, chickpeas Did you know? … Legume crops are nutritionally dense, containing vital proteins, minerals, and fibers. | → symbiotic relationship with bacteria at root nodules allow them to “fix” nitrogen from the atmosphere, pumping the soil full of fuel for future plant growth (great cover crops). → increase microbial activity (their chemical exchanges with plants) in soil. |
Brassicaceae (mustard or cabbage family) | cabbages, cauliflower, broccoli, kale, bok choi, turnips, brussel sprouts, mustard, radish, horseradish Did you know? … “Brassicas” originated from the same species, but diverged from one another when humans began selecting for different traits. | → competitive feeders that require heavy watering → cold tolerant properties (though, timing seeding properly is still crucial for many of the plants) |
Nightshades | tomatoes, white potatoes, eggplant, peppers, ground cherries Did you know? … Nightshades are “buzz pollinated” (and often wind pollinated too), which means that certain bees must vibrate the anthers of the flower to release pollen. | → competitive feeders that produce large fruits and/or roots, often draining nitrogen in the soil → highly susceptible to intrafamily disease → as heavy photosynthesizers, they may provide ample shade/groundcover for plants that need less direct sunlight (they, however, will thrive in warm, well-lit conditions) → contain toxic alkaloids (typically concentrated in foliage) that repel certain pests |
Cucurbits | cucumbers, melons, gourds, squash, pumpkins Did you know? … Cucurbits, in general, possess relatively lower nutritional value than other crops, and are also temperature sensitive, making them difficult to cultivate in certain regions. The rinds of some cucurbits have many different uses. | → vines provide extensive ground cover for cooling soil and surface-level moisture retention → foliage and roots grow quickly, with similar pattern distribution below and above ground → tough rinds protect fruits (seed bearing structures) from herbivores |
Chenopodiaceae (goosefoot family) | beets, spinach, Swiss chard, quinoa | → tolerate more basic soils (pH > 7; most plants of agricultural concern prefer slightly acidic environments) and saline (salty) environments → wind pollinated → have water retention properties |
Asteraceae (aster or daisy family) | lettuce, artichokes, sunflowers, safflower, tarragon, chamomile | → light and moderate feeders with rapid growth onset → bright flowers attract pollinators |
Alliums | onions, scallion, shallots, leeks, garlic, chives | → bulbs increase soil porosity, aggregate structure, and organic matter content → produce compounds that disrupt growth of fungal pathogens |
Umbellifers | carrot, celery, parsely, coriander, cumin, dill, fennel | → can grow in cooler weather → attract a wide variety of beneficial insects |
Lamiaceae (mint family) | basil, rosemary, sage, savory, marjoram, oregano, thyme, lavender | → strong aromatic smells repel pests, making them good companion crops → antimicrobial properties can inhibit bacterial/fungal pathogens in soil |
Give your garden a recovery period. Continual growth from annual plants can sometimes exhaust the land’s nutrient supply, so consider the following “recovery” rotations:
Composting & mulching: Adding these amendments to soil can help retain moisture in your agroecosystem, boost your organic matter content, improve drainage and aeration in your soil, and buffer temperature swings.
Fallowing: Fallowing is intentionally leaving a plot of land bare, with the hope that the added rest will promote the production of better crops in the future. There are differing stances on the utility of leaving a field fallow. Generally, farmers that use this technique believe it can alleviate weed pressure by first eliminating the competition for weeds, and then killing them off before they go to seed. At the same time, it is believed that without any crops growing, nutrient availability in the soil can recover, organic matter can build (by terminating weeds), and that the soil can soak up more water (less transpiration) for future crops. Among the possible drawbacks, fallowing for reducing weed pressure may entail using environmentally harmful herbicides or soil damaging tillage to destroy the weeds. Since fewer plants are grown in a year when fallowing a field, soil organic matter (SOM) may actually decrease due to less leftover crop residues. Finally, soil microorganisms that rely on plant structures (like mycorrhizal fungi’s reliance on roots) can experience serious disruptions with periods of fallow land.
Alternate (or sequence further apart) plant traits that are seen as “opposites.” Consider the following dichotomies:
Heavy feeding plant vs. nitrogen-fixing plant
Heavy feeding plant vs. light feeding plant
Extensive underground structures (root or bulb crops) vs. extensive canopy (above ground crops)
Shallow roots vs. deep roots
Consider using paired cropping and intercropping systems. Some plants grow better together (another lesson in itself!). Use pairings to maximize photosynthetic inputs, create shade for plants that need it, decrease weed pressure, enhance biodiversity, and create structures for other plants to grow on.
4. Using the information provided above, begin your crop sequencing scheme by answering these questions for own garden space:
What did we have planted last year, and the year before that?
What “crop families” [botanical families] do these things belong to?
How productive were these crops in these particular places?
Where are there perennials? Where are there annuals?
What are the market and/or individual needs for this year?
How many garden plots are there to rotate?
How many types of last year’s crops will be included in the rotation?
How many total (last year’s count + newly introduced) crops are included?
What is the total area of possible planting space (total planting area - area under perennial production)?
Where did we have pests last year? Where was the greatest weed pressure? Did you have any fungal or bacterial pathogens?
Were there any detectable patterns?
What controls were used?
How do you anticipate mitigating these harmful agents this year?
How will you encourage beneficial biological activity?
5. Finally, using the garden design template, design a cropping sequence based on your answers to the questions above. Make a list of each plot you have, what you had planted there last year, and what you will plant in the late Spring, Summer, and Fall. Check back with the principles above to verify that your crop sequence will yield good results. When you’ve reached the growing season, execute your crop rotations, and record qualitative and quantitative observations in a garden journal about any systemic changes you notice from day to day, season to season, and year to year.
Additional Resources:
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