Agrivoltaic agrotunnel/Sweet Potato Indoor Cultivation

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This guide explains how to use grocery-store sweet potatoes as mother roots, produce vine slips, and grow them in inclined 15-L coco-perlite buckets in the agrivoltaic agrotunnel. Grocery roots are suitable for trials, but their cultivar and disease status are uncertain; use certified, virus-tested slips when experimental reliability is essential.

Sweet potatoes are grown from vine slips, not by planting the whole root or root pieces in the final bucket. Whole roots take up growing space, may carry disease, and produce an uncontrolled number of shoots.

Choose roots that are:

• firm, smooth, and evenly coloured;
• medium-sized, about 200-400 g;
• free from mold, insect holes, deep cracks, soft areas, and black or sunken spots; and
• preferably organic or already showing one or two healthy buds.

Do not use refrigerated, badly shrivelled, leaking, damaged, or heavily sprouted roots.

If labelled roots are available, use Beauregard and Covington as separate treatments. Beauregard is generally earlier and can give high total yield. Covington often produces shorter, more uniform roots that may suit containers better. If the cultivar is unknown, record it as “orange grocery-store accession”. Do not guess the cultivar.

For every mother root, record the store, purchase date, label, country of origin, supplier lot, skin and flesh colour, and initial mass. Keep different roots and lots separate. Shoots from the same mother root are not independent biological replicates.

Surface sanitation reduces some fungal and bacterial contamination, but it does not remove viruses or internal infections.

• Plain, unscented household bleach. No detergent or splashless additives
• Potable water
• Free-chlorine test strips
• Gloves, a clean container, and a clean drying rack

1. Wash off soil and debris with potable water.
2. Prepare fresh chlorine solution at 120-150 ppm free chlorine and about 18-25°C.
3. Confirm the concentration with a free-chlorine test strip.
4. Immerse intact roots for 2 minutes.
5. Rinse once with clean potable water.
6. Air-dry on a clean rack for 12-24 hours.
7. Discard the chlorine solution after use.

Bleach required per litre of final solution:

Add bleach to approximately 90% of the required water, mix, and then add water to the final volume. Bleach loses strength during storage, so use the table only as a starting point and verify the final solution with test strips.

Safety: Wear gloves and provide ventilation. Never mix bleach with acids, vinegar, ammonia, alcohol, or hydrogen peroxide.

1. Place each whole sanitized root partly into moist coco–perlite.
2. Maintain 27-29°C and keep the medium moist, not saturated.
3. Wait for green shoots to develop.
4. When a shoot is 20-30 cm long with about 5-8 nodes and 4-8 healthy leaves, cut it using clean scissors.
5. Cut 1-2.5 cm above the mother root or substrate surface.
6. Plant the slip directly into its final bucket the same day.

A usable slip should be green, firm, and free of insects, lesions, wilt, and blackened tissue. Keep healthy leaves attached. Remove a leaf only if its blade would otherwise be buried and likely to rot.

If immediate planting is impossible, keep slips for no more than 1-2 days at 16-20°C in a shaded, ventilated container. Do not submerge them in water or seal them in a wet plastic bag. Pre-rooting in water is not recommended because the fragile water roots can be damaged during transplanting.

Inspect mother roots weekly. Discard a root and all its slips if black rot, internal discoloration, systemic wilt, or other serious disease develops. Disinfect tools between roots.

Use 70% buffered coco + 30% coarse horticultural perlite by volume. This mix balances moisture retention and aeration and reduces the risk of waterlogging on the lower side of a 45° bucket.

1. Fully hydrate and flush the coco.
2. Mix the coco and perlite evenly.
3. Fill each bucket loosely with about 15 L of substrate; do not compact it.
4. Leave 4-6 cm of space below the lowest part of the rim.
5. Pre-wet with nutrient solution at EC 1.0-1.2 mS/cm and pH 5.8-6.1.
6. Confirm that drainage holes cover the entire lowest area of the inclined bucket. No water should remain trapped below an outlet.
7. Run a test irrigation before planting.

The substrate should be evenly moist but should not release substantial water when gently squeezed.

For maximum marketable yield per bucket, begin with two slips per 15-L bucket. One slip may produce fewer but larger roots. Two slips are an experimental recommendation, not a proven optimum for this system.

1. Place the two slips on opposite sides of the bucket, 18-20 cm apart, at approximately the same height across the slope.
2. Make a 30-45° angled planting channel, 8-12 cm deep, for each slip.
3. Point the buried stems toward different parts of the central root zone.
4. Insert 8-12 cm of stem, placing 2-3 nodes below the surface.
5. Keep the growing tip and all leaf blades above the substrate.
6. Firm the substrate gently around the stem without crushing or sharply bending it.

Do not plant one slip at the top and the other at the bottom of the slope; they would receive different moisture conditions.

• With two drippers, assign one to each slip.
• Place each dripper 5-8 cm upslope from its slip, not against the stem.
• With three drippers, place the third near the center and slightly upslope.
• Do not place all drippers at the lower edge; this can saturate the downslope area while leaving the upper root zone dry.

Use frequent, small irrigation pulses. Check that water spreads through the root zone before draining rather than forming one narrow flow channel.

Immediately after planting, apply 0.5-0.8 L per bucket in two or three pulses, 10-15 minutes apart. Then use these starting conditions:

Keep the coco around the buried nodes moist but not saturated. If a slip remains badly wilted after 48 hours, check moisture around the stem, temporarily increase RH, and reduce light intensity.

Prepare separate 1:100 stock solutions for Calcium + Micros, Grow, and Bloom:

• Dissolve 100 g of each product separately.
• Add water until each stock reaches a final volume of 1.00 L.
• Each ml of stock then contains 0.10 g of product.

Never mix concentrated stock solutions directly together.

*Source-water EC varies. Always measure the final EC rather than relying only on the listed volumes.

To make 15 L:

1. Add 12-13 L of water to the reservoir.
2. Add Calcium + Micros stock and mix for 1-2 minutes.
3. Add Grow stock and mix.
4. Add Bloom stock and mix.
5. Add water to reach exactly 15 L.
6. Measure and adjust EC.
7. Adjust pH last to 5.8-6.2.

Suggested volume per irrigation event is 0.15-0.30 L during establishment, 0.25-0.40 L during vegetative growth and root initiation, 0.30-0.55 L during bulking, and 0.25-0.45 L during maturation. Adjust frequency and volume using plant demand, substrate moisture, and drainage. Do not follow a fixed volume if the lower bucket area remains wet.

• Guide vines laterally and slightly upward on a wide mesh, forming a fan.
• Keep vines from upper buckets from covering lower plants.
• Maintain a shallow, well-lit foliage layer where practical.
• Redirect long vines instead of routinely cutting them.
• Remove only diseased, dead, or severely shaded leaves.
• Prevent vine nodes from touching moist substrate outside the bucket, where they may form competing roots.

Avoid repeated pruning or leaf harvesting because it can reduce storage-root yield. Lift stray vines carefully and do not disturb the main crown.

Check and record at least weekly:

• plant health, pests, and disease symptoms;
• input and drainage EC and pH;
• irrigation volume and drainage percentage;
• temperature, RH, and light; and
• unusual wetness, dryness, salt buildup, or substrate movement in each inclined bucket.

Likely harvest windows are:

• Beauregard: inspect from 110-120 days; likely harvest at 120-150 days.
• Covington: inspect from 120-130 days; likely harvest at 130-160 days.
• Unknown or Japanese types: may require 140-180 days.

Indoor leaf yellowing is not a reliable maturity indicator. Use crop age, stabilization of water use and canopy growth, visible substrate displacement, and destructive sampling of a spare replicate when available.

During the final 3-5 days, reduce irrigation by about 30-50%, without wilting the plants. Stop irrigation about 24 hours before harvest only to make the coco easier to remove.

To harvest:

1. Cut vines 10-15 cm above the substrate.
2. Support the bucket horizontally.
3. Remove or split the container; do not pull the crown out.
4. Separate the coco gently by hand.
5. Handle roots carefully because fresh skin is easily damaged.
6. Do not wash roots before curing unless measurements require it.

Cure harvested roots for 5-7 days at 29-32°C and 85-95% RH, with gentle air exchange and no strong direct airflow. At the lower end of the temperature range, curing may take up to 10 days.

After curing, store roots in darkness at 13-16°C and 85-90% RH with moderate ventilation. Do not refrigerate below about 10-12°C, because chilling injury can occur.

• George et al. (2011), Root Piece Planting in Sweetpotato
• WSU Vegetable Research and Extension, Sweetpotato Slip Production and Sweetpotato Varieties
• LSU AgCenter, Sanitation in the Sweet Potato Packinghouse
• Sakamoto and Suzuki (2020), Nutrient Solution Concentration in Hydroponic Sweet Potato
• NC State Extension, Postharvest Handling of Sweet Potatoes