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Sweet Potatoes

Sweet potato (Ipomoea batatus) is an edible relative of the familiar blue-flowered weed called morning glory. It has heart-shaped leaves and spreads across the ground as a trailing plant that has small white or pink flowers.

It is also known by its Maori name of kumara. Although widely grown through the Pacific region, sweet potato is not native to the Pacific but has spread from Central and South America perhaps more than 1000 years ago.

Sweet potato is eaten roasted, boiled, steamed, or fried and can be used as a substitute for potato or pumpkin. Tubers are high in fibre and low in calories. Its low glycemic index (GI) makes it a useful food for diabetics. The leaves are also edible – pick young shoots as a spinach or silverbeet substitute.

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When to plant

Sweet potatoes need at least four to five months of warm to hot, frost-free weather to grow and produce worthwhile tubers. This length of the growing season may not be available in the coldest regions of Australia, especially where nights are cold. Check with hardware and garden centres for advice on your local conditions.

  1. Plant sprouted tubers in late winter or early spring in most areas.
  2. In cooler regions, wait until after all threat of frost has passed.
  3. In tropical regions, they can be grown all year round.

Location

  • Grow sweet potatoes in full sun or with light afternoon shade in hot climates.
  • Select a position with space for the 3m-diameter vine to spread. Grow in rows, mounds, raised vegie beds or against a trellis.
  • Sweet potatoes can be used as a summer ground cover under fruiting trees in well-fenced orchards to keep out predators.
  • They can also be grown in large containers and trained up a support such as a tripod.

Soil

Get the soil right to harvest a bumper crop of delicious, sweet potaotes.

Follow our steps for easy soil preparation.

Step 1 – Sweet potato tubers or cuttings (slips)

  • Sweet potatoes are grown from tubers or cuttings from a sprouted tuber or growing plant.
  • Find virus-free tubers in hardware stores, garden centres or online organic suppliers in late winter or spring.
  • In warm climates take tip cuttings as plants grow and use these to start new plants. Place the cutting into seed raising mixture such as Seasol Seed Raising & Cutting Potting Mix and water in the Seasol. This will help encourage strong root development and healthy leafy growth.
  • Potted plants may be available during late spring and summer.

Step 2 – Sprouting sweet potato tubers

  • Shoots may sprout unaided from healthy tubers, but the process can be sped up by either method below.
  • Cut a sweet potato in half and place it in a glass of water. Submerge half of it in the water and half out. Place in a warm  spot, either a window still or in the garden for several weeks, until shoots appear on top. Roots should also appear below.
  • Place tubers in a box of damp sand. Cover with about 5cm of sand. Stand the box in a warm spot.
  • Sprouted tubers are ready to plant when the sprouts have reached about 15cm long.
  • Cut the sprouted tuber into sections ready for planting into rich organic soil or potting mix.

Step 3 – Planting sweet potato tubers out

  • Plant sprouted tubers, slips, rooted cuttings or potted plants into well-prepared soil. Plant 7cm deep and at least 20cm apart.
  • When planting potted plants, follow the directions on the plant tag.
  • If planting into pots, use a container at least 40cm across to accommodate the growth and production of tubers.
  • Water sprouted tubers, slips, rooted cuttings or potted plants in with Seasol to reduce transplant shock and aid plant establishment.
  • Cover bare areas with 5-7cm of organic mulch to reduce weed growth while plants get established. Where weeds do grow, gently hoe to remove.

Step 4 – Sweet potato tuber growth

  • Allow plants to grow across the ground as a ground cover. Tubers form where the plants develop roots into the ground. Apply Seasol every week to fortnight to aid root growth and reduce stress from heat and drought.
  • Keep plants growing actively with regular watering and liquid feeding every 10-14 days with PowerFeed PRO SERIES for Tomatoes & Vegetables. Increase the application rates from 20mL to 50mL of concentrate per 9 litres of water as plants mature.
  • Excessive plant growth can be tip pruned or cut back. If growing in a pot with a tripod, ensure the vine is well supported by checking it regularly to ensure the vine is tied securely to the tripod.

Step 5 – Ongoing sweet potato care

  • As the plants spread, they naturally deter weeds. However, if weeds do occur, gently remove them by hand, being careful not to damage the vine.
  • Regular watering is vital, particularly in hot or windy weather, especially if plants are growing in a pot. On days of high heat check moisture levels morning and night.
  • Along with daily watering, light shade in hot districts can help protect vines from water stress.
  •  Every 6-8 weeks apply PowerFeed Controlled Release for Tomatoes & Vegetables to produce a bumper crop and to revitalise nutrient-depleted soils. Water in thoroughly after application to watch those microbes go to work.

Sept 6 – Preparing sweet potato tubers for harvest

  • Sweet potato tubers take 4-5 months to mature. Spring-planted vines will be ready to harvest by mid to late autumn as vines begin to die back.
  • Continue to liquid feed with PowerFeed Pro Series for Tomatoes & Vegetables every week.
  • Towards the end of their growth period, sweet potatoes will have taken a lot of nutrients out of the soil. To help replenish depleted soils apply Seasol Liquid Compost.
  • As autumn arrives and temperatures drop, it’s time to harvest sweet potatoes. Vines yellow and die back as temperatures fall.

Step 7 – Sweet Potato harvest

  • Tubers bruise and break easily so gently pull up or dig up the vine taking care not to damage the tuber. Damaged tubers don’t store well.
  • In a container or pot, simply tip out the container to easily harvest tubers, being careful not to damage them.
  • Allow tubers to dry for a few days, wipe free of soil then store in a cool, dark place for up to a month or in a plastic bag in the crisper section of the fridge.

Things to watch out for…

  • Animal pests Bandicoots, rabbits, rats and wallabies may attack plants and tubers. Where these animals are a problem, grow sweet potatoes in a fenced area or cover the ground with mesh around the base of the plant to prevent rodents from digging into the soil.
  • Frost damage Sweet potatoes are frost-sensitive and the above ground growth will be killed off by frosts.  Early frosts may reduce the size of the crop and may also damage tubers leading to rot.
  • Grasshoppers or caterpillars These insects may eat leaves but rarely do enough damage to affect the plant’s overall growth.
  • Tuber rot Tubers can rot in poorly drained soil. Rot may also occur if plants and tubers are frost damaged.

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