Overview
Cassava is one of the major staple foods of humanity, especially in the developing countries of the tropics where it provides a reliable source of calories when other crops may fail. The dense, starchy roots were historically a crucial food source for many indigenous groups throughout its native South America. Though technically a root, they are broadly thought of as a “tuber crop” in their cultivation and usage. It has now spread throughout the warm parts of the planet to become crucially important in tropical Africa, Asia, and beyond. In the case of Africa, cassava is the primary staple food of millions of people. This wide diaspora has given the crop many names such as yuca, manioc, tapioca, and endless variations on these. Cassava is eaten as a starchy, potato-like root vegetable but is also the source of tapioca starch, which has a myriad of food and industrial applications. Unlike most other root crops, which are herbaceous, cassava is a woody shrub. In my opinion, cassava is the most reliable yielder of all the starchy staples that can be grown in Central Florida. Yields are very high while labor and other inputs are relatively low. It performs exceedingly well in this climate and soil type. One friend who has traveled extensively through the tropics doing agricultural exploration commented that our cassava plants looked better than any he had seen anywhere else in the world. Cassava roots taste delicious and are highly sought after by people who grew up eating it, much as most Americans relish potatoes. It is in high enough demand to be available at many mainline grocery stores.
Climate Considerations
In the tropics, cassava is planted and harvested throughout the year. The physiology of the plant doesn’t limit it to a particular planting season nearly as much as most crops, provided there is a bare minimum of soil moisture present. While traveling in the countryside in the tropics it is common to see cassava at all different heights, oftentimes with singular farms having multiple fields planted at different times to provide staggered harvests throughout the year. Unfortunately this is not possible in Central Florida because of our subtropical climate. In fact, I find the situation to be quite opposite here with a very defined window of planting and harvesting bookended by potential frost or freeze events. Cassava is cold sensitive and does not actively grow in cool weather even if it is not frozen to the ground. If planted at the correct time, cassava is well suited to the Central Florida climate.
Cultivation Practices
Cassava is a thrifty plant that can grow in situations where other crops would fail, though it certainly responds to fertility inputs with higher yields. I generally “pocket amend” where the cutting will be planted with a few gallons of manure and compost and mulch the entire planting heavily. Top dressing with amendments throughout the season is helpful to plants.
Cassava is famous for it’s drought tolerance, though yields will be diminished or delayed by long periods of drought stress. I do not irrigate it on any sort of regular schedule, but I will intervene with emergency watering events during drought times, primarily in the early stages of the crop, which coincides with our dry season. Soil that is heavily enriched and thickly mulched will greatly reduce the need for watering. Always remember that just because the plants are surviving drought does not mean they are thriving. Diminished growth for the first three months of the season greatly reduces the capacity for potential yield, essentially representing lost time in the field. The yield of cassava roots seems to be directly correlated to the size of the plants. Big cassava plants with thick diameter stems mean big roots; small, stunted cassava plants mean small roots. Around the beginning of June plants should be approaching waist height. Cassava shows drought stress by yellowing and eventual dropping of lower leaves.
Cassava is a robust, woody plant that must have adequate space to grow. One plant can be fully expected to occupy a 4’x4’ space. There are a myriad of planting schemes that can be used on small farms and gardens. They can be scattered as individuals thought a mixed “food forest” or garden. In this case, be sure to provide adequate space from young trees and other crops as cassava plants cast deep shade and have competitive, greedy root systems. An agroforestry-based planting strategy I use is to plant a row down the middle of orchard tree rows. In following seasons the cassava will rotate with crops that follow the same timing scheme such as roselle, pigeon pea or true yams. Lastly, cassava can be planted in a block, like a cutout of a field. In the past I had always planted on a one-yard grid as is done throughout the tropics. Over several seasons I observed that the plants on the edge of the block would have much higher yields than those in the center. This occurs because they have the ability to have foliage on the side while the plants in the middle of the block compete for light and quickly make a full canopy and only maintain foliage at the top of the plant. More recently I have adjusted to 4’x4’ spaced plantings and am even experimenting with 5’x5’ spacing. I am confident the individual yield of each plant will be higher but it remains to be seen if this will yield a total higher yield per square foot. This decision may reflect if you wish to have larger roots to process all at once or small roots to use intermittently. Cassava plants can reach heights of 8’ or even much greater depending on growing conditions and variety.
My recent feeling is that a grid planting of cassava leaves a lot of unused space in the rows for a window of time that is long enough to squeeze in a short term intercrop and increase the productivity of the space. Legumes such as non-climbing cowpeas or bush beans may be viable options for the scheme. I am experimenting with a new planting technique (described below) that may open up the opportunity to intercrop with tropical pumpkins. Another intercropping idea I want to try is a legume cover crop that is grown between young plants solely for weed suppression and soil improvement. Jackbean is probably the best option based on low water needs, non vining form and high nitrogen fixing capacity. Jackbean/cassava intercropping is a major cassava farming strategy in Paraguay. This cover crop would be shaded out or cut and laid as mulch when the time is appropriate. A potential downside with these intercropping ideas is that they may complicate weed management.
Something I have discovered is that it is not necessary to pull out all weeds in the cassava patch, though it should be planted initially into weed free ground. Weeds, which rapidly colonize the rows, can be carefully string trimmed/weed whacked to ground level every few weeks. It takes some finesse not to damage the crop and not throw the mulch everywhere. This technique takes much less time and energy than a thorough weeding. The cassava plants are strong enough to compete against some weed pressure, as long as the weeds are kept at bay to some degree. Eventually the plants form a full canopy that is so dense no weeds can survive beneath it. This trait is phenomenal because the cassava growing area will be relatively weed free after the harvest.
One weakness of cassava is that it is quite prone to blowing over, especially when planted in singular rows. This seems to be a unique problem for sandy soils, as farmers working with clay based soils in Central America informed me in conversation that this is not a major issue for them. If plants fall over, they can be righted and tied off to a stake holding them upright, and soil piled onto the exposed roots. This can damage roots but yields can still be appreciable. Grid plantings are much less susceptible to this problem. Another way to deal with this is to drive bamboo poles down the row and attach horizontal pieces at a 3.5-4’ height and tie cassava stems off to the bamboo. Compact growing cultivars will be less susceptible to blowing over.
Propagation & Planting
Cassava is planted exclusively by cuttings in agriculture; with seeds generally only utilized in breeding programs. Seedlings can spontaneously emerge in farmer’s fields with variable mutations, which can be desirable or undesirable. Unlike many other tuber/root crops, cassava cannot be propagated from roots. Farmers and gardeners in different regions with varying conditions have different methods of planting cassava cuttings. Because cuttings are so hardy, they are planted directly in the ground where they will grow. Transplanting is possible but in my experience the roots will come out of the ground twisted from the influence of the pot early on in their growth. A Puerto Rican man taught me how to plant cassava and I have stuck with his method. He taught me to use a ten-node cutting, burying seven nodes and keeping three above ground. The cutting is planted at a 45-degree angle. To make the planting hole I jab a steel tamping rod into the ground at the correct angle and wiggle it around in a circular motion. I shove the cutting in to the correct depth, then collapse the soil onto the cutting with my hands quickly and move onto the next. It is important that the cutting is planted upright. Upside down cuttings will not grow. The growth buds occur above the leaf scar (where a leaf used to be attached). Observe the stem of a plant in the ground to get a good grasp of the correct orientation. When I have visited yuca farmers in Central America, they plant the cuttings completely horizontally a few inches deep. Another strategy I have used with success is digging a long, continuous trench and laying 4-5 foot cassava cuttings into the trench with the pieces butting up to each other. This technique works well and gives high yields but the plants are extremely susceptible to blowing over. This strategy deserves more exploration. This season I am trying a new technique wherein a 3’ cutting is planted vertically, with the same seven nodes buried in the ground. My hope is that with this technique it will open up the cassava patch to more intercropping in the beginning of the season. The initial growth occurs at the very top of the tall cutting, up and away from rambling neighbors, which would shade out the emerging plant with my standard planting method. About 1/3 into the current season this technique seems to be working fine with no apparent downsides.
In the tropics, cassava plants are always available so cuttings can be taken when needed. Central Florida has winter temperatures that often freeze the cassava plants completely, making fresh cuttings unavailable when the planting season arrives. This creates a bit of a conundrum, which fortunately has an easy solution. Incredibly, woody cassava cuttings can be stored for four months or longer for future planting. Before the first freeze arrives, I collect cuttings and tie them into bundles, carefully labeling each variety with a permanent marker. It is important to select long pieces, 4-5’ in length. I then stuff these cuttings into a shed, which has a sand floor and is situated in shade. I pile the bundles on the floor and make sure the door is shut for any hard freezes. This simple, low-tech solution has been fail-proof so far.
There are some selection criteria for getting the most optimal planting material. The thicker a cutting is, the more stored energy it possesses. Thick cuttings are faster growing and make more robust plants. The thickest cuttings come from the base of the mature plants. Thin stems from the top of the cassava plant are not worth saving for propagation unless it is a new, rare variety that calls for special attention. Another crucial selection point is how close the nodes are on the stem. This trait varies hugely on different parts of the plant. In some cases nodes can be so close they are jammed up together, and in other cases they are 6 inches or more apart. Since roughly seven nodes are buried in the ground, a cutting with widely spread out nodes would place the bottom of the cutting quite deep in the soil where tuberous roots will grow. Cassava planted this way will be virtually impossible to pull out of the ground without back injury, needless excavation and possible damage to the roots. To summarize, use thick stems with close nodes. All of the cutting work can be done with a sharp machete. When prepping cuttings, it is important to lay the stems down and hold the section to be cut firmly against the ground or the machete will split the stems and ruin them. I usually remove six inches or more from the ends of the long stems because the ends are often desiccated and dead. To check the viability of a cutting, scrape the bark with your fingernail. The presence of green underneath the scrape indicates a healthy, viable planting piece.
The best planting date for cassava in my garden is March 1st,, which is usually the last day a frost may occur. If the forecast looks hospitable I will plant them a week or two earlier. Delayed planting results in diminished yield. Occasionally a light frost can threaten in March. In this case, a one-gallon pot or a tuft of straw can be placed over plants for the night.
Genetics
The domestication of cassava represents a very complex lineage that probably involved several species contributing to give us modern cassava. It is extremely diverse and there are thousands of distinct forms grown throughout the world. Cassava is generally broken up into two distinct categories, “bitter” and “sweet” types. Raw cassava contains a toxic compound called HCN, which is a form of cyanide. Bitter types of cassava contain much higher concentrations of these compounds and require complex processes to make them edible. These varieties are still widely grown throughout the world because they are much more resistant to various forms of pestilence. Toxicity of bitter types should not be underestimated. I have encountered tales of death from improperly prepared bitter cassava while traveling. Simple precautions make cassava very safe to eat. Sweet cassava types are relatively low in HCN and can be eaten after relatively simple processing, such as boiling. There is no real compelling reason to grow bitter cassava in Florida. The great majority of cassava grown by gardeners in Florida is sweet but it is important to ask when receiving cuttings. Fortunately, the presence of toxic compounds is tied to bitter flavor so toxicity should make itself known upon tasting (Lebot 18). Sweet cassava will have a pleasant, nutty flavor that is free or mostly free of bitter flavor.
Cassava varieties come in many diverse forms and it is worth trialing varieties in search of those that have the traits we desire in Central Florida home gardens. Some varieties grow quite tall while others have a more compact form, which is more ideal considering their propensity to blow over during storms. Stems, leaves, tuber skin and tuber flesh come in a variety of colors. Most cultivars have white flesh but yellow types exist which contain beneficial beta-carotene content. Perhaps the most important trait for Central Florida is the amount of days to harvest. Some types are ready as early as 8 months, while some in the tropics can take 14 months. The Florida climate necessitates culture of early types that are ready to harvest before cold weather arrives. There are rumors of types that mature even sooner than 8 months but I have not encountered them yet. My favorite cassava variety I grow is named “Togo”, noting its West African heritage. This variety has a stout growth form, precocious and high production, is very easy to peel and tastes great.
Harvesting
The largest weakness of cassava as a crop is its pathetic shelf life. Roots begin to go bad within a week of harvesting, which is why roots sold in stores are coated in wax. Thus, cassava roots must be harvested relatively shortly before their desired use or preserved quickly for future use. The first harvestable roots appear in November and will continue to enlarge into late December. Plants can be harvested as-needed into Spring, but we have found that sometimes roots can become bitter when left in the ground over the whole winter. This bitterness presumably comes with an increase in HCN. I’m not sure what causes this but it may be a stress response from the plant. It is best to have cassava pulled out of the garden and processed by the end of February. Even if the tops die during winter the roots can survive underground waiting to be harvested.
Individual roots can be removed but it is easier and preferable to harvest whole plants at once. There is a special strategy to pulling out whole plants without damaging the roots. It takes a considerable amount of strength and can easily lead to a hurt back. Having a partner makes the process go smoother. It is important to do as little damage to the roots as possible because all damaged spots will contribute to spoilage. When harvesting, top the plant with a machete back to knee height and put all the stem material off to the side to give access to the base. To pull out the base, grab onto the remaining stem material and make a firm, consistent rocking movement. Once the roots become somewhat loose, add an upward pulling motion while continuing to rock. The whole root system will come up together still connected to the stem. Inexperienced harvesters often snap roots off underground. These roots have to be individually dug up and can be hard to find. The key to not snapping off roots is to be patient and pay good attention as you rock the plant. You can hear and feel when roots are on the verge of snapping. Freshly cut surfaces on roots will tell you if you have left part of the harvest in the ground. As top roots become visible it can be helpful to cut those away with the machete and harvest them so there is less resistance to the whole plant coming out of the ground. Unfortunately, higher yielding healthy plants are the hardest to pull out because their roots are long and deeply rooted. Once plants are out of the ground, they can be set on the ground and individual roots removed. Cut them away carefully with a machete, making one clean cut for each root as close as possible to where it connects to the stem.
Once the harvest is over, I fix the soil with my feet and compact it back to how it was before the mess was made. Any stem material desired for future plantings should be put away in storage. The remaining material can be chopped up with a machete and left as a mulch in the now open area where the cassava plant was. Cassava plants split into harsh angles that do not lie down easily for mulch. Cutting stems at all of their joints makes for straight pieces that lay down better. Some of these pieces may grow in the following season but they are easily killed by walking on them. Leaving behind this organic matter creates mulch that protects the soil and the nutrients that were in the plant biomass are returned back to the soil. If this type of coarse mulch is not appropriate for the location then the stems can be composted.
Pests & Disease
Cassava faces several important disease issues in the tropics, most notable is CMV (cassava mosaic virus). None of these diseases seem to have a presence in Central Florida at this point. Great care should be taken not to introduce these problematic diseases. Since cassava is propagated vegetatively, diseases pass to each new generation when they are planted by cuttings. People should not bring cassava cuttings into the United States that are potentially infected and put all Florida cassava growers at risk. In the future I will be growing all new varieties in a quarantined area away from the rest of my crop so I can observe to ensure I am not importing new pests.
Culinary Uses
There is a vast array of ways cassava is processed and prepared around the world. All of the methods include steps to detoxify the roots by removing most or all of the HCN content. The most straightforward way to eat sweet varieties is to peel the roots, dice them up and boil until soft. The water used to boil the cassava should be dumped and the boiled chunks can then be further seasoned and cooked in additional ways such as pan frying, mashing or baking. To peel cassava roots, cut the root into 1-2 inch wide “coins”. Then take a knife and hit it into the skin and pry up the edge. The peel will then roll off as one piece. There are two layers of skin, with the inner layer being white and harder to see. It is important to also remove this inner layer which is bitter and fibrous. The culinary aspects of cassava are too vast to cover in this post.
