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Quiz: DIY Systems and School Projects

Test your understanding of DIY hydroponic builds, beginner crop selection, school safety, and scientific project design with these questions.

1. What is the correct nutrient solution level relative to the net pot in a mason jar Kratky setup at the time of initial planting?

  1. Fill the jar completely so the net pot is fully submerged for maximum nutrient contact
  2. Fill the jar so the solution is about 1 cm below the bottom of the net pot, allowing an air gap to form
  3. Fill the jar exactly halfway and never add more water throughout the growing cycle
  4. Keep the jar empty until roots emerge, then add full-strength nutrient solution
Show Answer

The correct answer is B. The solution should just reach the bottom of the net pot (approximately 1 cm below), allowing a small initial air gap. As the plant absorbs solution and the level drops, the air gap grows, providing oxygen to the upper root zone. Fully submerging the net pot prevents the air gap formation that is the Kratky method's oxygen delivery mechanism. Never filling is incorrect — roots need contact with solution to absorb nutrients.

Concept Tested: Mason Jar Kratky Setup

2. What is the minimum acceptable EC range when introducing nutrient solution to seedlings after transplanting, and why is full-strength solution inappropriate at this stage?

  1. 2.0–3.0 mS/cm; seedlings need high nutrients to establish quickly
  2. 0.5–0.8 mS/cm; full-strength solution causes osmotic stress on fragile roots
  3. EC is irrelevant for seedlings — only pH matters during the first two weeks
  4. 1.5–2.0 mS/cm; seedlings need moderate nutrients but can handle adult concentrations
Show Answer

The correct answer is B. Seedling root systems are fragile and have high surface-to-volume ratios that make them vulnerable to osmotic stress. Full-strength nutrient solution (EC 1.5–3.0 mS/cm) can draw water out of young root cells, causing tip burn or wilting even with a full reservoir. Starting at EC 0.5–0.8 mS/cm and gradually stepping up over 7–10 days allows roots to acclimate while receiving adequate early nutrition.

Concept Tested: Seedling Transfer Timing

3. Why must a hydroponic reservoir be light-proofed, and what is the most effective method for a mason jar?

  1. Light causes nutrient minerals to settle out; wrap the jar in black electrical tape
  2. Light triggers algae growth; use a neoprene sleeve or two layers of aluminum foil
  3. Light raises solution temperature; paint the exterior with white heat-reflective paint
  4. Light disrupts root photoreception; keep jars in total darkness at all times
Show Answer

The correct answer is B. Light reaching nutrient solution triggers algae growth — photosynthetic organisms that bloom in nutrient-rich, illuminated water. Algae consume dissolved oxygen, cloud the solution, and compete with plants for nutrients. For mason jars, a tight-fitting neoprene sleeve (available as commercial hydroponic jar inserts) or a double-wrap of aluminum foil crimped around the glass provides effective light exclusion while allowing periodic inspection.

Concept Tested: Light-Proofing Reservoir

  1. Romaine — most nutritious and grows the fastest of all lettuce types
  2. Butterhead — minimal tip burn tendency, soft leaves, 28–35 day cycle, most forgiving variety
  3. Red Sails — the anthocyanin pigments indicate high mineral uptake efficiency
  4. Iceberg — forms tight heads that are ideal for measuring fresh weight at harvest
Show Answer

The correct answer is B. Butterhead varieties (e.g., 'Buttercrunch', 'Tom Thumb') are the most forgiving for beginners because they have lower tip burn susceptibility than romaine, form compact attractive heads, and have a fast 28–35 day harvest cycle. Romaine is prone to tip burn if calcium delivery is imperfect. Red varieties like Red Sails are appealing but the anthocyanin production requires adequate blue light. Iceberg is not recommended for hydroponic beginners.

Concept Tested: Lettuce Varieties

5. What is the correct air pump size selection for a single 5-gallon DWC bucket?

  1. The largest available pump — over-aeration is not possible in DWC systems
  2. A pump rated at 150 L/hr or more, sufficient for one gallon of reservoir volume
  3. A pump rated at 150+ L/hr is sufficient; approximately 1 L/min per gallon is the guideline
  4. Air pump size is irrelevant for small DWC systems — any aquarium pump works
Show Answer

The correct answer is C. The rule of thumb for DWC air pump sizing is approximately 1 liter per minute (L/min) of air output per gallon of reservoir volume. A 5-gallon bucket requires a pump rated at approximately 5 L/min (300 L/hr) at zero head. Most small aquarium pumps rated at 150+ L/hr work adequately for a single 5-gallon bucket. The pump should produce vigorous bubbling across the bottom of the reservoir, not just a thin stream of bubbles.

Concept Tested: Aquarium Air Pump Selection

6. In a classroom science fair hydroponic experiment comparing two EC levels, what is the minimum number of plant replicates required per treatment group for statistical validity?

  1. One plant per treatment is sufficient if measurements are taken daily
  2. Two plants per treatment is always statistically adequate
  3. At least three plants per condition to calculate a mean and standard deviation
  4. Ten plants minimum per treatment regardless of space or budget
Show Answer

The correct answer is C. A single plant tells you what happened to one individual — which may be an outlier. At least three replicates per condition allows calculation of a mean and standard deviation, enabling statistical comparison between conditions. This is the minimum standard for science fair and publication purposes. Two replicates technically allow averaging but provide insufficient information about variability within the treatment group.

Concept Tested: Science Fair Project Design

7. What electrical safety requirement is mandatory for all hydroponic pumps and grow lights operating near water in a school setting?

  1. All electrical equipment must be battery-operated to eliminate shock risk
  2. GFCI (ground fault circuit interrupter) protected outlets are mandatory for all equipment near water
  3. Equipment must be UL Listed at 24 volts or lower to be safe near water
  4. All electrical equipment should be unplugged when students are present
Show Answer

The correct answer is B. GFCI (ground fault circuit interrupter) outlets are required by electrical codes for all equipment near water — they detect tiny leakage currents and cut power in 1/40 of a second, preventing electrocution. In a school classroom with water-based hydroponic systems, GFCI outlets are mandatory, not optional. Extension cords must also be rated appropriately and should not run across walking areas.

Concept Tested: School Garden Safety Rules

8. What does "cut-and-come-again" harvest technique mean for loose-leaf lettuce, and what is the benefit over whole-head harvest?

  1. Cut the entire plant at the base and plant a new seedling in the same pot immediately
  2. Harvest outer leaves when 10+ cm long while leaving the inner growth point intact, enabling continuous production
  3. Alternate between two different harvest dates to keep continuous supply from one growing system
  4. Cut the plant back to the cotyledons every 7 days to stimulate vigorous regrowth
Show Answer

The correct answer is B. Cut-and-come-again harvesting removes only the outer, mature leaves (10+ cm long) while leaving the center growing point and young inner leaves intact. The plant continues producing new leaves from the center, extending the harvest period over several weeks rather than producing a single one-time yield. This extends the productive life of each plant significantly and provides continuous fresh supply, versus whole-head harvest which requires replanting after each harvest.

Concept Tested: Lettuce Varieties

9. Why should basil plants NOT be grown in nutrient solution cooler than 18°C?

  1. Cold solution slows basil germination but has no effect on established plants
  2. Cold solution causes root damage, wilting, and nutrient uptake failure in basil
  3. Basil requires cold solution to produce its characteristic aroma compounds
  4. Solution below 18°C causes basil to bolt prematurely and produce flowers
Show Answer

The correct answer is B. Basil is a warm-season herb that does not tolerate cold solution. Solution temperatures below 18°C slow root metabolism (reducing active transport of nutrients), can directly damage root cell membranes, and lead to wilting and poor growth even when other parameters are optimal. This is why cilantro (cool-season) and basil (warm-season) are sometimes alternated based on seasonal room temperatures rather than grown simultaneously at the same solution temperature.

Concept Tested: Herb Selection for Beginners

10. How does succession planting convert a feast-or-famine harvest pattern into continuous weekly yield from a single DWC system?

  1. Growing multiple crop species simultaneously so that different crops ripen in alternating weeks
  2. Starting new seedlings at regular weekly or biweekly intervals so a portion of the crop reaches harvest each week
  3. Harvesting half the plants each week and leaving the other half to continue growing
  4. Running the nutrient pump at variable speeds to slow some plants and speed others
Show Answer

The correct answer is B. Succession planting staggers seed starting dates by a fixed interval (typically 1–2 weeks). When executed correctly, a new batch of seedlings is transplanted into the system as an older batch is harvested, creating a continuous pipeline. For lettuce with a 35-day cycle, seeding every 2 weeks produces a harvest every 2 weeks rather than 16 heads all at once followed by a 4-week gap.

Concept Tested: Microgreens Production