By Cheryl Whalen, Head Gardener
Photos by Alison Rabinko
So here we are more than halfway through May and my activities in the tuberous begonia display house are well underway. For the past six weeks, I’ve been busy repotting begonias into their final pots for the season. This is also the time to try to root a few stem cuttings which, with any luck, will yield tiny new tuber tots by fall.
Of course the begonias are not all ready to be potted up on the same day. Each plant roots into its starter pot according to its own whim. It’s a process. You will find me most Saturday mornings throughout spring quite content in my makeshift workshop in the begonia house tending to those begonias that are ready to make the move. Gently knocking each plant out of its pot, I look for a network of fibrous roots that pretty much covers the outer surface of the soil mass. If the root system is not developed enough, the plant goes back to the bench and I wait another week.
The upright display plants get transplanted into 10” clay pots. The potting process is simple. With plant and pot in front of me and my barrel of potting mix at my side, I get busy. After filling the pot to nearly halfway with soil, I set in the begonia being careful not to sink the top of the root ball too deeply. I sprinkle a half teaspoon of a slow release fertilizer like Osmocote in the soil around the plant. Then I follow up with more soil to fill the pot, pressing lightly on the soil surface to firm it in. I pop in the plant nametag so our guests can be properly introduced to each variety when they visit the nursery. Everyone gets a thorough watering to settle them into their new digs. With words of encouragement, back to the bench each begonia goes eager to get growing.
I have found that some of the tuberous varieties tend to have lots of active eyes that grow up into a plant with many stems. It’s quite possible to cheat a few of these stems away from the tuber with no ill effects. These stems can be rooted, and in time they will form new tubers and become the newest additions to my family.
I take these cuttings right before the plants get moved up to their final pot. First, I select the stem I want to take. Then, with the root ball exposed, I peel back the soil until I can see where that stem attaches to the parent tuber. Looking closely at the very base of the stem, I spy a tiny pinkish bud. I need to make sure that when I make my cut that I am below that bud. Without that bud, the stem will make only roots but never a tuber. With the tip of my knife, I carefully cut and sort of pop the stem off of the tuber.
Most times the stem cuttings already have some young fibrous roots attached. With the cutting in hand, I trim away some of the leaf surface area to prevent wilting until those tiny roots can take hold. Using my multitasking Sharpie, I dibble a hole in the soil of a small pot, and I plant the stem. One inch of the stem should be undercover in the soil. I water in the fresh cutting and place it with the others in the shady spot in the back of the greenhouse. For the first week or so, I spritz the cuttings with water a few times a day until the roots can catch up and provide adequate water to the top growth.
Our mail order tubers are still born and raised in England. I like to make my stem cuttings from the tuberous begonia varieties that are part of our collection but not currently found in the for-sale list. So sometimes I am able to offer our store visitors the chance to purchase a variety or two that they could not have purchased otherwise from our catalog. My selections for purchase in the begonia house do vary from year to year.
Stem cuttings are not the only way to make more begonias, but it’s the one way I’ve tried so far. I would like to investigate other propagation possibilities just to satisfy my own curiosity. If only I had some more spare time . . . To be continued . . .
(To see previous chapters in the life cycle of Tuberous Begonias, scroll down.)