Tuberous begonias are a vibrant and beautiful flowers that are commonly sought after as a prize piece in many gardens. However, the tuberous begonia is quite uncommon in the unique growing experience that the plant's cultivation process offers the gardener. Whereas many other flowers germinate and sprout from simple seeds the tuberous begonia, as its name implies, grows from a tuber. Basically it's a root like plant structure that looks like a shriveled, misshapen potato.
While the tuber may not look like much it is significant, and choosing a tuber that is appropriate to your level gardening experience is an important first step in growing complex and colorful begonias. We'll explore some of the unique opportunities attached to working with tubers in contrast to seeds and point out some things to avoid if you're new to the begonia racket.
Selecting Your Tubers
Begonia enthusiasts insist that the best way to source your tubers for potential Begonia tuberclosa cultivars is to go straight to the source. In this case that means trying to get your hands on a tuber from a plant that has already bloomed successfully under someone else's care and has since seen the flower and bloom portions die off and regress back to a very alive, very nutrient rich tuber that will lay low during the plant's off season. Because begonias can regrow and have multiple blooms across seasons from a single tuber, it is unlikely that a beginner could acquire a tuber with such a proven history, unless you already happen to have a friend with a green thumb and generous heart.
More likely, you'll be going to a store and purchasing tubers to begin your planting. Be aware, tuberous begonia cultivars tend to be expensive when compared to other plant or flower seeds, but even with that caveat the pricing varies wildly depending on the strain. Arguably the best producer of begonia plants with the finest flowers is Blackmore and Langdon, based out of the United Kingdom. Because of their sought after quality, a single tuber for a Blackmore and Langdon plant can run you as much as forty to fifty dollars. If you have the passion and some historic successes with other tuberous begonias, feel free to splurge for the top drawer tuber.
Though if you're not comfortable or confident enough in the fact that the plant won't die on you before any flowers bloom, it's a smarter choice to settle to for a low to middle range supplier that price in a range between 15 and 30 dollars. Plus those producers usually offer multiple tubers in a single package for that same amount. Assuming that you follow all of the correct growing practices, your worst case scenario with a cheaper tuber is that you may not have the fanciest flower of all, but you will come out of the blooming season with a beautiful begonia.
So you've finally acquired the ideal shriveled little potato. Now what? First judge the weather and season for your region. Tuberous begonias are frost sensitive plants with an optimal growth and bloom period that peaks from July through September. As such, if you are starting with a mere tuber you should plant sometime in the Spring in anticipation of flowers in the following months. But be careful, as wild begonias are native to high altitudes so intense summer heat and direct sunlight is a killer. If you live in such a climate, tuberous begonias can actually be grown indoors. The best option here is to find a locale such as an east facing window, where the indoors protect the plant from the heat without depriving it of at least a few hours of light a day.
At the start, the cultivars are very needy so be sure to use a healthy soil and provide a healthy diet of fertilizer when necessary. A good mixture to establish and encourage early growth is equal parts potting soil, peat, and sterile sand. The sand is significant as it promotes good drainage, and issues such as over watering and rot getting to the tuber are common and fatal mistakes that novices tend to make. As an added precaution against poor drainage, some gardeners even plant their tuber deliberately at the very bottom of their pot and water from below.
After 2-6 weeks you should be seeing some growth and even some leaves. It is at this point that the sprouts should be transplanted to whatever location it will ultimately stay in when it blooms, either to the outdoor soil or to a larger pot. As your stem gains height and surpasses 6 inches, consider placing a stake in the ground to offer support. For safety press your stake close enough for the stem to be attached but still slightly off center so you don't accidentally stab the submerged tuber.
From this point forward, maintenance is the main goal as the plant just needs time to grow. Continue to ensure that the soil is getting good drainage and be aware that as the plant grows and even blooms, additional stints and supports may be needed to help carry the weight of the large vibrant flowers.
When your lovely flowers finally begin to shed and die toward the end of the summer be sure not to uproot your tuber prematurely. In fact, the best way to ensure that the tuber stays healthy and productive for the next season is to allow it to stay potted and continue to receive water and nutrients for as long as November. Even if there is little to no growth during this period, any nutrients absorbed are stored within the tuber.
Finally dig out the tuber along with some of its surrounding soil. Place it out in the open and allow it dry and shed some of the dirt and soil that may be stuck to it. When the final small excess stems break from the cured tuber, store it in sand or dry peat moss and keep it at a cool temperature such as 50 degrees Fahrenheit.
If your blooms are successful and your tuber is preserved, you can begin the entire process again when the weather allows for it.