Sweet potato is a great vegetable that is reasonably easy to grow if the conditions are suitable for the plant, and mulch is one component that helps create good growing conditions; even in areas outside of the natural locations where it grows natively, it can be successfully grown with care.
Sweet potato vines should be mulched when planted to maintain soil moisture content, suppress weed growth, and to protect microbiology at the soil surface-root zone interface.
There is plenty of information on growing sweet potatoes on the net, and while a lot is very generic, it seems not much is written by actual growers of these plants.
We are happy to say that we do grow sweet potatoes, and we also consider ourselves to be self-sufficient in this root crop, and through this, we would like to help others start growing this wonderful vegetable.
So to explain this article a little, it is written to convey the techniques and methods that we use and know to be effective for us, so I hope that at least something in this post can help all visitors.
A few common questions come up from time to time about growing sweet potatoes, so we address these as we go.
What can be used as mulch for sweet potato?
Many things can be used as mulch for growing sweet potatoes, and the primary purpose is maintaining moisture in the soil.
Organic materials like recycled paper, cardboard, bark chips, straw, hay, shredded trees, and even small tree branches laid side by side will all be effective. The sweet potato tubers will push up from the ground and make space as they grow.
Some suggest that mulch can keep weeds down, and while this may be applicable when the sweet potato is very young, the vines will quickly outgrow any weed that does come up, so don’t get hung up about them.
Sweet potato can become a thick mat of green leaves that can form an excellent ground cover. However, the moisture loss from bare or un-mulched soil still happens but at a less rapid rate because of the shading by the plant’s leaves.
Mulch will help even more if it holds nutrients that the vines can access as it breaks down. This is how we approach growing sweet potatoes.
We have a related article explaining how this nutrient-rich mulch can be beneficial. It is titled “Growing lots of ginger: is this the best mulch?” It is a little off-topic for sweet potatoes, but the mulch information is precisely what we look to do with our sweet potato patches.
Commercial growers often use a black plastic sheet as a mulch substitute to increase soil temperatures. Sweet potato loves heat, and warm soil is the best environment for it to grow. The plastic cover allows the soil to maintain moisture, and before the daily temperatures climb too high, the vines have sprawled to create protective shade for the roots.
Hot soil is detrimental to the plant, whereas warm soil is prime. This is one of the reasons that sweet potato is challenging to grow in colder climates. If you are in a tropical or sub-tropical zone, the soil temperatures will be fine in early to mid-spring.
The plant will grow in these zones during the winter; however, if frost is a regular occurrence where you live, then best wait till the frosts are behind you.
The image below is a small section where we have sweet potatoes growing wild. We harvest annually, leaving a few tubers to set the following year’s supply in motion. The smaller seedlings are rosellas that have self-sown. This is all under the dripline of a mango tree.
The mulch you see is wood shavings from wood turning on a lathe similar to that described in the above-linked article. If you have skipped reading it so far, we suggest reading it to wrap your head around the “why” some mulches work better than others.
The link (all links) will open in a new tab so you won’t lose your place here.
How thick should mulch be for sweet potato?
The thickness of the mulch can vary, and what you have available to use as mulch will dictate how thick a layer is ok. Cardboard sheets from recycled boxes are good as just a single sheet, but you may want to cover it for looks.
A layer of hay over the cardboard is all you need to get going and will last for the season. The soil needs to be loosened before you plant your sweet potato slips, and they can be planted once the cardboard is down and holes have been cut where the plants can go.
The mulch we use is in a layer up to 8 inches thick (200mm) but will vary quite a bit. The minimum is about 4 inches (100mm).
The thickness of some mulches can stifle the airflow because the mulch is a barrier like cardboard. In contrast, the wood shavings we create as a byproduct of lathe work allows airflow and water passage. It also holds slow-release nutrients.
Rainfall can easily move through this mulch, and you should think about your mulch situation regarding this.
How much water does sweet potato need?
Sweet potato is a tropical plant; like all plants from these areas, it loves moisture. It is easy to have soil that is too wet, and this can cause the tubers to rot in the ground.
The sweet potato will perform best when the soil is kept moist through regular watering without creating conditions that can rot the tubers before harvest. As the crop matures the watering can be slowed a little to help avoid the risk of rot.
The people of the New Guinea highlands form mounds of loose soil into which they plant sweet potatoes, and this allows the extreme rainfall events that are common in that part of the world to run off and cause no harm.
This method works, and as the sweet potato is a staple food source for these people, the ways of planting that they rely on can be a lesson for us all to observe and then put into practice in our gardens.
We also grow sweet potatoes in raised bed gardens, and we use different mulch on these. The image below shows the covering on the bed. It is a light-colored organic sugar cane mulch that helps reflect some of the heat from the soil surface.
Raised beds get warmer than in-ground gardens, so we try to compensate through different methods. This seems to work ok so far, but this is just the second year of this method, so we will find out if we are right in our guess.
In fact there are several disadvantages to growing in raised beds as we detail in “Organic raised bed gardening : what are the disadvantages?” and soil heat is a big one.
Growing any vine in a raised garden bed can cause damage to the vine as it escapes the confines of the garden bed if the edges of the bed are sharp, so to help avoid this, this article “Can edges on corrugated steel garden beds be made safe?” details a way to help.
Will mulch increase sweet potato yield?
Mulch will definitely increase the harvest yield but how much by is impossible to say.
This is an unknown quantity because there are so many variables to consider. It is a regular event for us to harvest 20 pounds (10 kgs) of tubers from a 3ft x 3ft patch of the garden when grown using the nutrient-rich mulch described in the first linked article.
There is no reason why this number cannot be larger if more work is done on the soil before planting out. We apply the mulch each season and let it do its own thing.
We even grow rosellas over the top of the sweet potato, and the self-sown seeds for the coming season have already popped up and are raring to go. It does take a little time to keep the vines off the rosella plants, though. Sweet potato vine will climb.
Some fertilizers can be placed under the mulch; these should not be nitrogen-rich because they encourage heavy vine growth and do little to zero for the tuber quantity.
We sometimes use a light sprinkle of our version of organic fertilizer that we have the chickens make for us, as described in this article titled “Improve your garden soil with rock dust and chickens.” It is a critical process in maintaining soil fertility here in the tropics, where heavy annual rainfall can leach nutrients faster than you can blink.
Most plants benefit from a good protective layer of mulch. While the plants will often grow without the mulch layer, in a situation where self-sufficiency and food resilience are concerned, it is a significant component towards some level of reliable food growing.
The yields from bare soil sweet potato gardens can be far less and of inferior quality. We recommend the methods we use, and applying mulch is a major process we won’t sidestep.
If you have not begun to grow this crop yet and need to work out what you need to start, “Sweet potato propagation, tips for backyard food growing” is recommended.
Article by Tim Blanch for TheTropicalHomestead.com. He is a qualified Permaculture designer.