Sweet potato / Kumara (Ipomoea batatas) growing guide

Quick facts

Category: roots bulbs
Difficulty: intermediate
Days to harvest: 90 to 150 days
Harvest type: single harvest then replant
Spacing: 30 cm between plants

Environment

Temperature: 18–32°C
pH: 5.5 to 6.8
EC (hydroponic): 1.4 to 2.2 mS/cm
Daily light: 20 to 30 mol/m²/day

Climate and zones

USDA zones: 8 to 13 (winter low around -12°C or warmer)
Frost tolerance: frost sensitive (dies at first frost)
Season: warm (summer crops, frost-sensitive)

Viable growing environments:

outdoor in growing season (annual)
unheated greenhouse / hoop house
heated greenhouse
indoor (heated home)

USDA zone bounds reflect outdoor year-round survival. Anywhere outside the bounded zone range, this crop still grows as an annual in the warm months (outdoor_seasonal), under cover (greenhouse), or indoors under lights.

Growing systems

Sweet potato works in:

media bed (ebb and flow)
wicking bed
soil bed

Root mass is very heavy - thin-channel systems (NFT, vertical towers) can't hold this crop mechanically, hence the system list above.

Growing media

The substrate the roots sit in. Choice depends on the system (clay pebbles don't fit NFT channels; rockwool isn't used in media beds) and the crop (sweet potato works in the media listed below).

Medium	pH effect	Water retention	Bacterial surface
Soil-based mix (Potting soil)	varies by source	high	high
Coco coir (Coconut coir)	slightly acidic	high	moderate

Bacterial surface area matters for aquaponics: clay pebbles, lava rock, and pumice double as biofilter substrate. Low-surface media (rockwool, perlite, pea gravel) work in hydroponics but need a separate biofilter in aquaponics.

Nutrient demand by stage

NPK ratios are relative weights at each growth stage; the nutrient mix calculator scales them to absolute grams or ml. EC targets shift through the plant's life: seedlings need a much lighter solution than fruiting adults.

Stage	N	P	K	EC target (mS/cm)
seedling	2	1	1	1.2
vegetative	2	1	3	1.8

Companion-growing notes

Heavy uptake of potassium. Co-grown crops with the same demand will end up deficient even at "correct" EC. Plan around this in shared reservoirs.
High transpiration. Reservoir level will need regular top-ups during fruiting or flowering.

Aquaponics suitability

Compatible with typical aquaponics nutrient profiles. Fish waste provides enough nitrogen for healthy growth; supplemental potassium, calcium, and iron may still be needed depending on fish stocking density.

Care notes

A warm-season root crop for media beds or large containers (20 L) with loose substrate. Not suited to NFT or DWC (the storage roots form in the growing medium). EC 1.5-2.5 mS/cm. pH 5.5-6.5. Temperature: 22–32°C (tropical; frost kills the vine, and tuber formation stalls below 18°C). High light (DLI 18-28 mol/m2/day). Propagation: from slips (small rooted shoots grown from a sprouted sweet potato). Place a sweet potato in water with the bottom half submerged; shoots emerge in 2-4 weeks. Twist off individual slips when 15–20 cm long, root in water, and plant. From transplant to harvest: 90-120 days. The vine grows vigorously and can be trained vertically or allowed to sprawl. Harvest when the vine starts to yellow, by digging carefully. Cure tubers at 30°C and 85% humidity for 5-7 days to convert starches to sugar and heal skin wounds, then store at 13–15°C. The sweet potato leaves and vine tips are a bonus harvest: cook as greens throughout the season.

Notable varieties

A starting shortlist of cultivars worth knowing about. Not exhaustive: the seed catalogs list hundreds of named varieties. These are the ones home growers commonly choose between.

Cultivar	Type	Breeder / origin	Days	Notes
Beauregard	open-pollinated	Louisiana State University, 1987	100	Orange flesh, copper skin. The dominant US commercial variety; ~80% of US sweet potato acreage. Disease-resistant and high-yielding.
Covington	open-pollinated	North Carolina State University, 2005	105	Orange flesh, similar to Beauregard but with better storage and disease resistance. Has displaced Beauregard in much of the North Carolina commercial trade.
Murasaki	open-pollinated	Louisiana State University, 2008	110	Purple skin, white flesh. Drier and starchier than orange-flesh types; the Japanese-style sweet potato (closer to the Stokes Purple style).
Stokes Purple	open-pollinated		120	Deep purple flesh, dry and dense. Very high anthocyanin content. Slower to mature than orange types; not suitable for short-season zones.
Georgia Jet	open-pollinated		90	The shortest-season sweet potato available. Specifically bred for the upper South / lower Midwest where the season is too short for Beauregard. Orange flesh, productive in 90 days.