Now, which side of the tuber is the up side? And which side is the down side? We get dozens of calls every year about which way is the correct way to plant these cup-shaped tubers. It’s simple to remember: Plant the cup-shaped tuber UP! If you happen to plant them upside-down, the sprouts will eventually grow to the surface — they will survive — but the sprouts will have to grow down and around the tuber to get to the soil’s surface, and that’s a waste of time. Plant the cup-shaped tuber UP, and you’ll be on the way — the right way!
Keep the planted tubers moist and at room temperature until the sprouts appear, which doesn’t take long. At all stages of growth, begonias are kept in strong light, but not directly in hot sun. When the first shoots appear, it’s time to begin feeding with a weak 5-10-5 or liquid manure fertilizer every week. Fertilize carefully — be careful not to burn the little plants by splashing fertilizer onto the leaves.
Where are you going to use your tuberose begonias? Use them wherever you want precious color in the shade or in tree-filtered light. These shade-loving plants can best be used in protected areas — they’re quite fragile. What’s a protected spot? NOT where the hose gets pulled through the evergreens and pachysandra. NOT where the kids play ball, and NOT where the paper person throws the newspaper. NOT where a broken downspout pours a torrent of water from the roof during every rainstorm. And beware of unleashed dogs that might run through your begonia plantings! Consider using them in containers for a lush, luminous look.
For the most spectacular blooms, continue feeding begonias all summer. During the summer, remove dead flowers and foliage to prevent fungus and mildew. Good air circulation helps prevent mildew, which is common on most begonias.