Table of Contents
- Introduction
- The Standard Rule for Begonia Planting Depth
- Why Planting Depth Matters for Begonias
- Planting Tuberous Begonias Step-by-Step
- Dealing with Begonia Transplants and Wax Begonias
- How Spacing and Depth Work Together
- Preparing the Soil for Proper Depth
- Container Planting: Depth and Pot Selection
- Starting Begonias Indoors vs. Direct Planting
- Timing Your Planting
- Watering Strategies for New Tubers
- Conclusion
- FAQ
Introduction
Begonias are a favorite for adding vibrant, tropical color to the shadier corners of your yard. Whether you are growing trailing varieties in hanging baskets or upright begonias in garden borders, these plants offer a long season of beautiful blooms. At Longfield Gardens, we enjoy helping you find the right plants to make your outdoor spaces feel like a personal retreat. Getting started with begonias is simple, but success begins with one important detail: planting depth.
Setting your begonias at the correct depth ensures the roots have enough room to grow while keeping the stems and tubers safe from rot. This article will guide you through the specifics of planting tuberous begonias and wax begonias, whether you are starting them in the ground or in containers. By following a few basic rules, you can enjoy healthy, vigorous plants that bloom from midsummer all the way until the first frost.
The depth at which you plant your begonias depends primarily on the form of the plant—whether you are starting with a dormant tuber or a nursery-grown transplant.
The Standard Rule for Begonia Planting Depth
When you are working with tuberous begonias, the general rule is to plant the tuber about 1 inch deep. This means that after you place the tuber in the hole, you should cover it with approximately 1 inch of loose, well-draining soil. This depth provides enough weight to anchor the plant as it grows while allowing the young sprouts to reach the surface easily.
If you are planting wax begonias or other varieties already growing in nursery pots, the rule changes slightly. These plants should be set at the same depth they were growing in their original containers. You want the soil level of the garden bed to match the soil level of the root ball. Planting these too deep can lead to stem rot, while planting them too shallow can cause the roots to dry out too quickly.
Key Takeaway Tuberous begonias should be covered by 1 inch of soil, while started transplants should be planted level with the existing soil line.
Why Planting Depth Matters for Begonias
It might seem like a small detail, but planting depth plays a critical role in the health of your begonias. Begonias are succulent plants, meaning their stems and tubers hold a significant amount of water. This makes them highly productive bloomers, but it also makes them sensitive to excess moisture.
If a tuber is planted too deep—three or four inches down—it may struggle to send shoots to the surface. The cool, damp soil at that depth can cause the tuber to rot before it ever has a chance to sprout. On the other hand, a tuber planted too shallow might not develop a strong enough root system to support the weight of the heavy flowers and foliage later in the season.
Proper depth also helps with temperature regulation. Begonias are tropical plants that love warmth but can be sensitive to extreme heat. A 1-inch layer of soil acts as a thin blanket, keeping the tuber insulated from rapid temperature swings in the early spring while allowing it to feel the warmth of the sun as the season progresses.
For a broader look at begonia types and care, see All About Begonias.
Planting Tuberous Begonias Step-by-Step
Tuberous begonias are grown from firm, brown, disc-shaped tubers. They are famous for their large, rose-like blooms and their ability to thrive in partial shade. Because the tuber is the lifeblood of the plant, how you position it and how deep it goes will determine your success for the year.
For more growing tips, see Tips for Growing Tuberous Begonias.
Identifying the Top and Bottom
Before you dig, you must know which side of the tuber faces up. Tuberous begonias have a distinct "hollow" or indented side and a rounded, smoother side. The hollow, bowl-shaped side is the top. This is where the leaf sprouts will eventually emerge. The rounded side is the bottom, where the roots will grow.
If you see small, pinkish buds (often called "eyes") in the hollow area, those are your future stems. Always plant with the hollow side facing the sky.
Digging the Hole
For each tuber, dig a hole that is roughly 2 to 3 inches wide and about 2 inches deep. Because begonias prefer loose soil, we recommend fluffing up the soil at the bottom of the hole before placing the tuber. This makes it easier for the new roots to penetrate the ground and start seeking out nutrients.
Placing and Covering
Place the tuber in the center of the hole with the hollow side up. Gently crumble loose soil over the top until the tuber is covered by 1 inch of soil. Do not pack the soil down too hard with your hands. Instead, give it a light pat to ensure the soil is in contact with the tuber without crushing the delicate buds.
What to do next
- Identify the hollow side of the tuber.
- Dig a hole 2 inches deep.
- Place the tuber hollow side up.
- Cover with 1 inch of loose soil.
- Water lightly to settle the soil.
Dealing with Begonia Transplants and Wax Begonias
Many gardeners purchase "wax begonias" or started tuberous begonias in plastic cell packs or small pots. These are already growing and often have several sets of leaves or even a few flowers.
Matching the Soil Level
When you move these plants into your garden or a larger pot, the most important thing is consistency. Dig a hole that is as deep as the root ball in the pot. When you slide the plant out of its container, place it in the hole so that the top of its root ball is level with the surrounding garden soil.
Avoid "Mounding"
A common mistake is to mound soil up around the stems of the plant. Since begonias have fleshy, soft stems, burying them in soil can trap moisture against the stem, leading to "damping off" or stem rot. If the plant feels a little wobbly after planting at the correct depth, simply press the soil firmly around the roots rather than adding more soil higher up the stem.
How Spacing and Depth Work Together
While depth gets the plant started, spacing allows it to finish the season strong. If you plant your begonias at the perfect depth but put them too close together, they will compete for light and air. Begonias are susceptible to powdery mildew, a fungal issue that thrives in humid, stagnant air.
For tuberous begonias, we suggest spacing the tubers about 10 to 12 inches apart. This gives the foliage plenty of room to expand. Wax begonias, which are often used as a colorful groundcover or edging, can be planted slightly closer—about 6 to 8 inches apart—to create a "carpet" effect of color.
By combining the 1-inch planting depth with 10-inch spacing, you ensure that each plant has its own "zone" of soil to draw water from and enough airflow to keep the leaves dry and healthy.
Preparing the Soil for Proper Depth
The depth of your planting is only as good as the soil you are planting into. Begonias need "well-drained" soil. Drainage refers to how fast water moves through the soil. If water sits in the hole like a puddle, your begonias will not be happy.
Amending the Soil
If your garden soil is heavy clay, it can be difficult to maintain a consistent 1-inch depth because the soil doesn't crumble easily. We recommend mixing in some compost or finely ground bark before you plant. This loosens the texture, making it easier to tuck the tubers in at the right depth.
Testing Drainage
Before planting, you can test a spot by digging a small hole and filling it with water. If the water drains away in less than an hour, the spot is perfect. If it takes several hours or a full day, you should consider planting your begonias in raised beds or containers where you have more control over the soil environment.
For more shade-friendly planting options, browse our spring-planted bulbs for shade.
Container Planting: Depth and Pot Selection
Begonias are among the best plants for containers because they provide constant color without needing full sun. When planting in pots, the rules for depth remain the same, but you have a bit more flexibility with spacing.
If you are planting trailing or hanging begonias, planting them near the edge of the pot will encourage them to spill over the sides more quickly.
Pot Depth and Size
For a single begonia tuber, a 6-inch or 8-inch pot is usually sufficient. If you are using a large whiskey barrel or a deep planter, you don't need to fill the entire thing with begonia tubers. However, because these pots are deep, make sure you use a high-quality potting mix that doesn't stay soggy at the bottom.
In a container, you can plant tubers about 4 to 6 inches apart for a fuller look. Still, maintain that 1-inch covering of soil over the top of each tuber. If you are planting trailing or "hanging basket" varieties, planting them near the edge of the pot will encourage them to spill over the sides more quickly.
For even more combinations, see our container shade collection.
Using High-Quality Potting Mix
Avoid using garden soil in containers. Garden soil is too heavy and will pack down, effectively making your 1-inch planting depth feel much "heavier" and wetter than it should be. A lightweight, peat-based potting mix with added perlite (those little white volcanic rocks) is ideal for keeping the tubers aerated.
Key Takeaway In containers, use lightweight potting mix and maintain the 1-inch depth, but you can space tubers closer together (4–6 inches) for a lush, full display.
Starting Begonias Indoors vs. Direct Planting
Because begonias are tropical and take some time to start blooming, many gardeners choose to "wake them up" indoors before the weather is warm enough to plant outside. This is a great way to get a head start on the season.
For an early start, read How to Start Tuberous Begonias Indoors.
The Indoor Method
If you start indoors, you can plant the tubers even more shallowly at first. Place the tubers in a shallow tray filled with damp potting mix. Instead of burying them an inch deep, just press them into the soil so the tops are level with the surface. This allows you to monitor the buds as they sprout.
Transplanting to the Garden
Once the tubers have sprouted stems that are 2 to 3 inches tall and the outdoor temperatures are consistently warm, you can move them to the garden. At this stage, you should follow the transplant rule: plant them so the top of the tuber (and the base of the new stems) is just barely covered by soil.
Timing Your Planting
Timing is just as important as depth. If you plant your begonias at the perfect depth but the soil is still freezing, they will not survive. Begonias should only go into the ground when the danger of frost has passed and the soil has warmed up.
A good rule of thumb is to wait until nighttime temperatures are consistently above 50°F (and ideally closer to 60°F). In most parts of the United States, this happens in late May or early June. If you are eager to get started, remember that the "wait" is part of the process—planting in warm soil leads to much faster growth than planting early in cold, wet soil.
To check your location, use the Hardiness Zone Map.
We ship our bulbs and tubers based on the appropriate planting time for your specific USDA hardiness zone. See our Shipping Information page for details on timing and delivery.
Watering Strategies for New Tubers
After you have tucked your tubers into the soil at that 1-inch depth, the next step is the first watering. This is a critical moment.
Settling the Soil
The goal of the first watering is to settle the soil around the tuber so there are no large air pockets. You don't need to soak the ground until it is muddy. A light, gentle watering is enough.
Avoiding "The Hollow"
One specific tip for tuberous begonias: try to water around the tuber rather than directly into the hollow center. Because the top of the tuber is shaped like a bowl, water can sometimes collect in that indentation. If the weather is cool and the water doesn't evaporate, it can lead to rot. Once the plant has grown several inches and has plenty of leaves, this is less of a concern because the leaves will act as an umbrella and the plant will be using water much faster.
Ongoing Moisture
Keep the soil consistently moist, like a wrung-out sponge. If the soil at the 1-inch depth feels dry to the touch, it is time to water. If it feels wet and sticky, let it dry out for a day or two before watering again.
Conclusion
Planting begonias at the right depth is a simple step that sets the foundation for a summer full of spectacular color. By keeping tuberous begonias 1 inch deep and setting transplants level with the soil, you provide the perfect environment for these tropical beauties to thrive. Remember to choose a spot with filtered light, use well-drained soil, and wait for the warm weather to arrive.
At Longfield Gardens, we want you to feel confident in your garden. Gardening is a rewarding way to connect with nature, and begonias are some of the most generous plants you can grow. Our 100% Quality Guarantee helps make that possible. With just a little bit of care during the planting phase, you will be rewarded with lush foliage and stunning blooms that last for months.
For more shade-loving inspiration, browse our summer flowers for shade.
- Plant tubers 1 inch deep with the hollow side facing up.
- Space plants 10 to 12 inches apart to allow for airflow.
- Wait until nighttime temperatures stay above 50–60°F.
- Use well-draining soil to prevent rot.
Success with begonias starts with the right depth and the right timing. Once they are settled in, these plants are remarkably easy to care for and will provide beauty all season long.
FAQ
Can I plant begonias in full sun?
Most begonias prefer partial shade or filtered light, especially in the afternoon when the sun is strongest. However, some newer varieties of wax begonias are bred to handle more sun. Always check the specific light requirements for the variety you have chosen, as too much direct sun can scorch the leaves.
Which way is up on a begonia tuber?
The "up" side is the indented or hollow side, which looks a bit like a shallow bowl. This is where the stems will grow. The rounded, smooth side is the bottom and should be placed facing down into the soil.
What happens if I plant my begonia tubers upside down?
If a tuber is planted upside down, it will still try to grow, but the stems will have to grow around the tuber to reach the surface. This uses up a lot of the plant's energy and results in a much later start to the blooming season. If you realize you’ve planted one upside down early on, you can gently dig it up and flip it over.
Should I add mulch over my begonias after planting?
While mulch is great for many plants, use it sparingly with begonias. A very thin layer of organic mulch can help retain moisture, but you should keep it away from the stems. Thick mulch can trap too much moisture against the fleshy stems and tubers, which may lead to rotting.