GROWING AN EDIBLE TUBERS

A tuber is an edible root produced by a number of plants of various species. Tubers are grown worldwide and have been cultivated by humans for thousands of years. There are very many tubers that can be grown, so it is important to choose one that is right for your area. This guide will cover the kind of tubers we sell at Raintree Nursery.

HORSERADISH

Soak in water up to 30 minutes to re-hydrate, then plant in a pot or in the ground. Keeping horseradish in a container may help you control its spread, but don’t let the roots grow out of the drain holes into the ground.

Use a potting mix designed for vegetables, and keep evenly moist. In the ground, horseradish will appreciate the addition of finished compost mixed into the top foot of soil.

WASABI

Wasabi grows best at 46-64°F. Grow under a shady leaf canopy unless summers tend to be cool and foggy. Above 70°F the plants may experience fungal disease or leaf burn, below 45°F they stop growing. Temperatures below 27°F may kill the plants.

Plant so the crown (the point where the leaves meet the roots) is about ½”above the soil. Amend the soil with finished compost 1 foot deep to provide plenty of humus and good drainage, then plant.

Keep plants cool on warm days with mist, but do not over-saturate the roots. In cold winter locations grow wasabi in pots using a well-drained vegetable garden mix, a 2-3 gallon pot should produce a nice sized root.

YACON

Yacon is hardy to 10°F, or colder if the dormant roots do not freeze in winter. Tops will die down with the first frost. Plant when all danger of frost has passed, in a rich well-drained soil, pH 6.5-7.2.

Plant in a mound amended with compost if your soil is heavy. Mulch the Yacon with compost to encourage strong growth and conserve moisture, keep soil evenly moist when actively growing. Tubers require about 200 frost free days to mature, and will be sweeter following frost. Plants can be started in a container in short-season locations, then planted outdoors when risk of frost has passed.

Use a garden type potting mix in a 1-2 gal pot, keep in a bright light situation, 50°F minimum temperature, and water regularly if the plant is growing.

OCA

Hardy to 0°F, Oca needs a pH range from 6.0-7.2, and well-drained soil.

Yields will improve with the addition of compost. Keep the soil evenly moist during the growing season, hill once or twice like you would a potato plant. Tubers begin to form as day length decreases, protect from frost in the fall to increase potential tuber size.

Start tubers in a container, use a well-drained mix for vegetables, and plant out after danger of frost. Or plant them directly in well-drained garden soil. Store the harvested roots at room temperature for several days after harvest to harden the skins and reduce the amount of oxalis, then store cool and dry.

MASHUA

Although it can be grown in many parts of North America, the Pacific Northwest is especially well suited to mashua cultivation.

The tubers should be planted in a sunny location during spring after all risk of frost has passed. Start mashua indoors in pots to get a head start on the season. They are tolerant of most types of soil, so long as they are moist, with a pH range of 5.3-7.5. Support or plenty of space will be needed for the vigorous trailing vines. Hilling after first emergence and at first flower may increase harvest. The tubers are ready for harvest in 6-8 months, or following first frost. They form near the surface and are harvested like potatoes.

Store the tubers up to 6 months in a cool, well ventilated location that is protected from strong light. Tubers left behind in the ground will sprout the following spring.

USDA HARDINESS ZONE

Most tubers are hardy to USDA zones 4-9, unless otherwise noted. This rating tells you the minimum winter temperature the plants typically survive when properly hardened off. On our web site you will find a USDA Hardiness Maps which provides information on the average minimum winter temperature in your location, by zip code.

CHILL HOURS

Many plants native to locations that have cold winters have a Chill Hour requirement to ensure uniform waking up of flower and leaf buds in the spring. The chill hour requirement of plants varies by species, by cultivar, and sometimes by the level of dormancy achieved.

WHERE TO PLANT YOUR TREE

Most tubers, with the exception of wasabi, need to be planted where they receive at least 8 hours of direct sunlight measured in early summer (late June to early August). Sufficient sun exposure triggers the initiation of new flower buds for the next growing season, without which there will be no root growth. Tuber ripening and flavor development are also benefited by the carbohydrate production stimulated by the sun, as well as it’s heat.

Tubers generally tolerate a wide variety of soils so long as they are well drained and moderately rich with a pH around 6.3-6.8. Improve your soil where you intend to plant by mixing an inch or two of plant based organic matter (manures are best for vegetable gardens), peat, or coconut coir into an area 1 1/2 to 2 times the diameter of the needed planting hole and up to a foot deep. A 2-4” deep layer of mulch (straw, leaves, or wood chips) applied after planting will continue to improve the soil.

Allow sufficient space for both the top of the tree and it’s roots when selecting the planting location. Refer to size descriptions for each variety, keeping in mind these are generally managed or pruned sizes, not maximum potential sizes. If you are planting an orchard be sure to include enough space between rows for transporting supplies in and fruit out.

GROWING IN CONTAINERS

Many tubers are excellent grown in a container if managed and harvested regularly, especially those the require the extra heat and drainage that a container can provide.

CARE AND MAINTENANCE

WATERING YOUR TREE

This is the most important and often the most difficult part of successfully growing plants. There are many factors, including the humidity, temperature, soil type, wind, and amount of direct sun that affect how much and how often water should be applied.

A general rule of thumb for plants in the ground is to ensure they receive an inch of water per week over the root zone. An inch of water is equivalent to about ¾ to one gallon per square foot of soil surface area. The typical three foot diameter planting hole would need 7 ½ to 10 gallons of water per week provided by rainfall or by the gardener.

Apply this water once a week, two times per week if soil is fast draining. This will of course depend on your own conditions and the plants you are growing! DO NOT waterlightly each day because this results in a wet surface and dry root zone area. The soil should be moist but not soggy to a depth of about a foot for most growing plants. The top inch or two can feel dry, and the plant still be well watered. The trick is to have the water available where the roots are. In hotter and sunnier areas, a mulch of straw, bark, etc. can greatly ease the burden of summer watering. For plants in containers, water until the soil is saturated and water comes out of the drainage holes. Let the container dry until the soil is dry to the touch 1-2 inches down and the container is lighter in weight. A plant that has wilted canbe receiving either too much or too little water.

In rainy areas like the Pacific Northwest most of the plants that we offer will need relatively little supplemental irrigation ONCE THEY ARE WELL ESTABLISHED in the ground and have had a chance to develop a good root system. However even here it is important to make sure plants have regular, deep watering during the first couple of growing seasons, and the first summer is especially critical. In drier areas, permanent irrigation is essential. Remember that you don’t want your trees to just survive, but rather to thrive. Make sure they get the water they need.

One method is through drip irrigation. We use half- inch flexible plastic pipe with punch-in emitters for trees in the ground. For each young tree, we use two emitters, spaced one foot from the trunk. The pipe can be put on the ground, under the ground with risers, or tied loosely from the trees. We use emitters that drip one gallon per hour. See drawing above. There are many different styles of drip systems, some controlled by timers and others by hand. Or, each tree can be watered with a hose deeply about once a week. Sandy soils will need more frequent watering than clay soils. For smaller plants, like strawberries or raspberries, soaker hoses work very well.

FERTILIZATION

For good steady growth and high productivity, your trees need to have adequate amounts of various mineral nutrients. Some people are fortunate and have naturally rich fertile soil. Many soils, however, are deficient in some nutrient or another and use of fertilizers, organic or chemical, can be highly beneficial if you want your trees to grow well. If you have a large gardener orchardist can be well worth it to have your soil analyzed by a qualified laboratory so you know for sure just what your soil needs. Typically this might cost $30-$60, depending on how detailed an analysis you want. Unless you know what is available in your soil, you will not be able to supplement it properly.

Use an all-purpose or balanced fertilizer like the organic fruit tree and shrub fertilizer. A couple of inches of well-rotted compost on the root zone can also be an effective fertilizer. A generous leaf or straw mulch around your trees will not only conserve moisture and help in weed control, but also keeps your soil healthy by building up humus, attracting earthworms, and supporting beneficial fungal organisms. This encourages young trees to be strong, healthy and productive. Use of concentrated products like chemical fertilizers or strong organics (for instance blood meal) is usually done from late winter through early summer. Applying fertilizer after early summer can encourage lots of soft new growth that is much more likely to be damaged by winter cold. Excessive use of fertilizer can in-crease disease problems on your plants and can even kill them. Use of too much fertilizer, whether chemical or organic, canals contribute to stream and groundwater pollution, so please try not to use more than your trees really need. As a general guide, if your tree is producing about one foot of new growth or more a year and has healthy looking foliage, it may not need much or any fertilizer.