Vegetable Gardening for Engineers

This is a starting point for understanding how to grow vegetables at home. I created this document out of dissatisfaction with popular gardening books (too little detail) and social media (too much talking and clickbait). I found myself organizing and synthesizing concepts, data, and advice from disparate sources. I even turned to material from agricultural university extension programs, crop guides from commercial seed and fertilizer companies, high school biology courses, live farmer training courses and gardening workshops, and techniques from indoor cannabis growers.

This document reflects my personal learning journey over the past years. You are welcome to submit pull requests or email me with feedback.

Currently the focus is on indoor and balcony growing in an urban apartment setting. Therefore, only hydroponics and container gardening are covered. Garden beds, composting, aquaculture, fungiculture, permaculture are not covered (yet).

Table of Contents

This document is organized broadly in three parts:

  1. 🍎 Concepts
    1. ☯️ Environmental parameters
    2. 🌱 Growth stages
    3. ☀️ Light
    4. 🌡 Temperature
    5. 🧪 Nutrition
    6. 🟤 Growing Media
    7. 💧 Water
    8. 😷 Pests and diseases
  2. 🔢 Data
  3. 🛠 Techniques & Resources
  4. 💰 Economics

The first part provides a conceptual understanding of the science of growing vegetables. The second part features tables of data (“VegTable”) for many garden crops. It answers basic questions about crop selection. The third part is a collection of links about well-known growing systems, techniques, and other resources. Finally, the last part examines the economics of market gardening.

🍎 Concepts

☯️ Environmental parameters

When growing plants, your task is to balance a number of highly interdependent factors, as listed below. An insufficient amount of, say, light or nutrition creates a limiting factor in plant growth and development. On the other hand, excessive light or fertilizer (i.e. beyond what a specific plant species can handle at a given metabolic rate) can also result in problems (tip burn, photo-oxidative stress).

Parameter Measurement Unit Zone
Light Daily Light Integral (DLI)* mol/m²/day Light
Temperature Air temperature* °C Air
Humidity Relative Humidity (RH) % Air
Wind Wind speed m/s Air
Carbon dioxide (CO₂) Carbon dioxide ppm Air
Nutrients Electrical Conductivity (EC)* μS/cm Soil/Water
pH pH* pH Soil/Water
Temperature Root-zone temperature °C Soil/Water
Oxygen (O₂) Dissolved Oxygen (DO) ppm Soil/Water

* key measurements for small-scale systems

Why are these relevant? Plants perform two critical processes which are complementary:

Light is the single most important environmental parameter as it literally provides energy for plant growth.

Temperature dictates a plant’s metabolic rate and therefore also strongly influences growth rate.

Additionally, there is another critical process:

Soil pH is sometimes called a “master variable” as it affects the solubility of soil nutrients (among other things, including microbial activity) and therefore nutrient availability, hence plant growth.

Air humidity, wind, and temperature all affect the rate of transpiration and also therefore nutrient uptake and plant growth. For this reason, poor ventilation actually can result in nutrient deficiencies.

On the other hand, excessive ventilation decreases relative humidity which, in combination with heating the cooler incoming air (air holds more water at warmer temperatures), can increase transpiration, which decreases plant temperature and increases ambient humidity, resulting in a vicious cycle. Alternatively, if transpiration occurs to the extent that there is not enough water in the plant (e.g. during peak hours of the day), then stomata (microscopic openings on the undersides of leaves) will close, which increases leaf temperatures and decreases CO₂ exchange… [1]

Humidity can be reduced in three ways: 1) heating (air holds more water at warmer temperatures), 2) ventilation (“out”), and 3) condensation (“in”).

Environments:

More about plant biology

🌱 Growth stages

Stage Description Labor
Germination (Stage 1) Sowing to radicle (root) emergence -
Germination (Stage 2) “Sprout”: Radicle emergence to expansion of cotyledons (false leaves) -
Germination (Stage 3) “Seedling”: Cotyledon expansion to vegetative growth -
Vegetative Growth of all true leaves Transplant
Flowering From first flowering to first fruit set Pollinate*
Fruiting* From first fruit set to growth, ripening, and first harvest -
Maturity From first harvest to the end of last harvest Harvest

* fruiting crops only

A general rule of thumb is to plant seeds twice as deep as they are large.

More about plant growth

☀️ Light

Light Quality

Based on https://en.wikipedia.org/wiki/File:EM_spectrumrevised.png

Light quality refers to the distribution of wavelengths (colors) in a light. The part of the light spectrum most relevant to photosynthesis is 400–700 nm. This range is named Photosynthetically Active Radiation (PAR).

Simplistically speaking, blue light is needed to produce healthy stems and leaves. Red light is needed for flowering and fruiting, as well as seed germination, root growth, and seed production.

Historically it was believed that plants only used PAR light. It is now understood that far-red and ultraviolet light, which are both outside PAR, can affect plant development. Specifically, far-red (FR) light, which penetrates leaves, can tell plants that they are under a canopy and promote growth, whereas blue-violet and ultraviolet light, which are abundant in the sky, can inhibit growth.

Shopping advice:

Light Quantity

Based on https://en.wikipedia.org/wiki/PI_curve

The rate of plant growth scales to light quantity (intensity). However, below a certain quantity (the light compensation point), there is not enough energy to fuel growth. On the other side, above a certain quantity (the light saturation point), plants become damaged. Tolerance levels vary from crop to crop (see the Data section).

Light quantity is measured in various ways, with a key metric being Daily Light Integral (DLI).

Measurement Unit Meaning
Photosynthetic Photon Flux (PPF) μmol/s The amount of PAR (400–700 nm light) emitted from a source per second.
Photosynthetic Photon Flux Density (PPFD) μmol/m²/s The amount of PAR that reaches a destination per second.
Daily Light Integral (DLI) mol/m²/day The amount of PAR that cumulatively reaches a destination in one day.

PPFD and DLI are spot measurements. They are always relative to a specific distance from the light source.

To calculate DLI, multiply PPFD × hours of light per day (“photoperiod”) × 1/1000000 mol/μmol × 3600 sec/hour.

Shopping advice:

Photoperiodism

Photoperiodism refers to how the light cycle affects plant growth and flowering. Short-day plants (e.g. lettuce) only flower when days are shorter than a certain length, long-day plants (e.g. mung beans) only flower when days are longer than a certain length, and day-neutral plants (e.g. tomatoes) flower based on other conditions.

More about plant lighting

🌡 Temperature

Every plant has a base (minimum) temperature (T𝘣𝘢𝘴𝘦), an optimal temperature (T𝘰𝘱𝘵), and an maximum temperature (T𝘮𝘢𝘹). These temperature ranges can vary across growth stages.

Crucially, there is a tradeoff between growth rate and growth quality. Higher temperatures can result in faster growth but also thinner stems, weaker roots, and less flavor. Furthermore, gases become less soluable at higher temperatures, increasing the risk of oxygen deficiency.

Key air temperature measurements are as follows:

Measurement Unit
Average daily temperature (ADT) °C
Difference between day and night temperature (DIF) °C
Growing degree days (GDD) °C-day

Higher DIF can result in taller plants with weaker stems (stem elongation).

Unlike air temperatures, root-zone temperatures need to be relatively stable.

Plants can be grouped according to their tolerance for cold temperatures:

More about plant temperature

🧪 Nutrition

Plants require 17 essential nutrients (“minerals”) for survival.

Of these, plants obtain carbon (C), hydrogen (H), and oxygen (O) freely from air (CO₂ and O₂) and water (H₂O).

The remaining nutrients are obtained from the soil (or alternative growing media) in the form of salts. This happens through multiple processes: by the root physically growing in contact with the nutrients (“root interception”), by dissolved nutrients flowing through the soil solution to the root (“mass flow”), and by dissolved nutrients diffusing through the soil solution to the depleted soil next to the plant root (“diffusion”).

Nitrogen (N), phosphorus (P), and potassium (K) are required in the largest amounts; commercial fertilizers are labeled with N-P-K ratios. Although nitrogen is abundant in the atmosphere (N₂), it is only available to plants in the form of ammonium (NH₄⁺, which has an acidic effect), nitrate (NO₃⁻, which has a basic effect), and urea.

Nitrogen is a key ingredient in many plant substances, including chlorophyll. It is used by leafy green crops (like lettuce) and more in the vegetative growth phase of fruiting crops. Phosphorus and especially potassium are more important for fruiting crops (such as tomatoes), as evidenced in the following diagram showing the macronutrient uptake across time for a tomato plant:

Based on https://www.haifa-group.com/crop-guide/vegetables/tomato/crop-guide-tomato-plant-nutrition

Electrical Conductivity (EC)

A EC meter measures electrical conductivity, which is an indicator of the amount of dissolved nutrients (mineral salts) in a solution.

Notes:

pH

Source: https://commons.wikimedia.org/wiki/File:Truog_1947_pH_and_nutrient_availability.jpg

pH is the measure of acidity or alkalinity (basicity) of a solution, where acidic refers to having a high concentration of hydrogen ions (H⁺).

Soil pH is highly important as it affects the bioavailability of nutrients to plants.

Shopping advice

More about plant nutrition

🟤 Growing Media

Soil is best understood from three perspectives simultaneously:

Porosity refers to the percentage of pores (microsopic spaces) in the growing medium which can contain water or air. Different media have different water-holding capacity. For example, coarse-grained media (such as foam) has a low water-holding capacity (i.e. holds onto water weakly), medium-grained media (such as rockwool) has a medium water-holding capacity, and fine-grained media (such as peat) has a high water-holding capacity (i.e. holds onto water strongly). Water-holding capacity and air porosity should be chosen to be appropriate for the crop and container size.

💧 Water

TBD

🔢 Data

See overview table at https://github.com/CollapseLabs/gardening-for-engineers/blob/master/crops/dist/_crops.csv and individual pages at https://github.com/CollapseLabs/gardening-for-engineers/tree/master/crops/dist

The size and maturity values provided are for comparison purposes only. Actual values will vary considerably depending on seed variety, climate and other environmental factors, and growing technique.

😷 Pests and diseases

TBD

Key here is to take an ecological (ecosystems) perspective.

🛠 Techniques & Resources

Vertical farming refers to indoor farming in an urban context, scaling vertically, based on an early concept of farming in New York City skyscrapers. It implies the use of artifical lighting, either as a supplement or a replacement for sunlight. A vertical farm is also known by the Japanese term Plant Factory with Artificial Lighting (PFAL). Vertical farming may or may not involve vertical-plane growing (i.e. growing vertically in towers, as opposed to growing horizontally in racks).

Controlled-environment agriculture (CEA) refers to growing in a climate-controlled environment, typically a greenhouse but can also be completely indoors.

Hydroponics

Techniques:

More about hydroponics:

Online courses:

Automation:

Greenhouse growing

Container gardening

Automation:

Backyard/allotment gardening

Methodologies:

Techniques:

General gardening/urban ag courses

Companion planting

Urban agriculture & market gardening resources

TBD

Economics

For a typical hydroponic greenhouse (source: ZipGrow):

See also