Table of Contents
- Introduction
- The Magic Number: Temperature Requirements
- Soil Temperature Matters
- Timing Based on Your Growing Zone
- Dormant Tubers vs. Started Plants
- Starting Indoors for Earlier Blooms
- The Essential Step: Hardening Off
- Choosing the Right Outdoor Spot
- What to Do if a Late Frost is Predicted
- Signs Your Garden is Ready
- Specific Timing for Different Begonia Types
- Water and Fertilizer After Moving Outside
- Monitoring for Pests in the Spring
- Long-Term Planning for Begonia Health
- Caring for Begonias in High Heat
- Conclusion
- FAQ
Introduction
Begonias are a favorite for many home gardeners because they bring incredible color to the shaded corners of a yard. Whether you love the massive, rose-like blooms of begonias or the lush foliage of Rex varieties, these plants offer a long season of beauty. At Longfield Gardens, we want to help you enjoy those vibrant flowers from the moment you move your plants into the garden. Getting the timing right is the most important step for success with these tropical treasures.
In this guide, we will cover the exact temperature and weather conditions begonias need before they head outdoors. We will look at how your local climate and planting zone affect your schedule. This information is designed for anyone who wants a lush, healthy garden without the guesswork. By following a few simple rules about warmth and weather, you can ensure your begonias thrive all summer long.
The most important thing to remember is that begonias are tropical plants that love warmth and cannot tolerate cold. For a broader overview of begonia types and care, see our All About Begonias guide.
The Magic Number: Temperature Requirements
The most common question we hear is about the specific date to plant. While a calendar can give you a rough idea, begonias care more about the thermometer than the date. These plants are native to tropical regions.
For the best results, wait until the danger of frost has completely passed. In most regions, this is several weeks after the "official" last frost date. Begonias really start to grow when the air and soil are warm. If you put them out too early, they may sit still or struggle to grow later in the season. For more practical growing tips, see our Tips for Growing Tuberous Begonias guide.
We recommend waiting until nighttime temperatures stay consistently above 50°F. If you want to be extra safe, wait for 60°F nights. This higher temperature is the "sweet spot" where begonias feel at home and begin to put on new leaves quickly. Warm nights are the signal the plant needs to start its summer growth cycle.
Soil Temperature Matters
Air temperature is only half of the story. The soil temperature is just as important for the health of the roots or tubers. Even if the afternoon sun feels warm, the ground often stays cold much longer into the spring. Cold, damp soil can cause begonia tubers to sit dormant or, in some cases, even rot before they get started.
Aim for a soil temperature of at least 60°F. You can check this easily with a basic soil thermometer pushed a few inches into the ground. If the soil is still cool to the touch, it is better to keep your plants in their pots on a warm porch or inside a little longer. Waiting for the ground to warm up actually leads to faster growth and earlier flowers in the long run.
Plants that go into warm soil establish their roots much faster. A begonia planted in warm June soil will often catch up to and even pass a plant put out in cold May soil. This is one of those cases where being patient for an extra week or two leads to a much more rewarding garden.
Timing Based on Your Growing Zone
Your USDA hardiness zone is a helpful tool for planning your gardening year. While begonias are only perennial in very warm climates like zones 9 through 11, they grow beautifully as annuals everywhere else. Understanding your zone helps you estimate when that 60°F threshold will arrive, and our Shipping Information page shows how Longfield Gardens times shipments by zone.
In northern zones, such as zones 3 through 5, you might not be able to plant outside until early to mid-June. These areas often have "late" frosts that can surprise gardeners in May. In central zones like 6 and 7, mid-to-late May is usually the safest window. Gardeners in the south can often plant in April, provided the spring rains have moved through.
Always keep an eye on your local 10-day forecast before you move plants. If you see a dip into the 40s or low 50s, keep the begonias tucked away. Local weather patterns can vary from year to year, so use your zone as a starting point and your local forecast as the final word.
Key Takeaway: Begonias thrive when night temperatures stay above 60°F and the soil is warm to the touch.
Dormant Tubers vs. Started Plants
The "when" of planting also depends on what you are planting. If you are planting dormant tubers directly into the garden, you must wait until the soil is warm. Dormant tubers have no leaves yet, so they are entirely dependent on soil heat to wake up. This usually happens in late spring.
If you are transplanting begonias that already have leaves and flowers, they are even more sensitive. These plants have been growing in a warm greenhouse or inside your home. They are used to stable, warm conditions. Moving them into a cold garden can be a shock to their system.
For started plants, the "when" is strictly after all danger of frost is gone. For dormant tubers, you can plant them once the soil is 60°F, even if there is a tiny lingering risk of a very light frost, because the tuber is protected underground. However, waiting for settled, warm weather is always the safest path for both.
Starting Indoors for Earlier Blooms
Many gardeners choose to start their begonia tubers indoors about 8 to 12 weeks before the last frost. This is a great way to get a head start on the season. By the time the weather is warm enough to go outside, you will have a sturdy plant with several leaves or even some flower buds.
If you start your begonias indoors, you don't have to wait for the tubers to wake up in the garden soil. You simply wait for the weather to be right and then move the established plant outside. This can result in flowers that start in early summer rather than mid-summer.
When starting indoors, use a shallow tray or small pots with high-quality potting mix. Keep them in a warm spot, around 70°F, and provide plenty of indirect light. Do not move these "spoiled" indoor plants directly into the garden without a transition period.
The Essential Step: Hardening Off
"Hardening off" is the process of getting plants ready for the transition from indoors to outdoors. This is a critical part of the "when" because it determines exactly when your plants are physically ready to live outside. Even if the temperature is perfect, a plant moved directly from a still house to a breezy garden can suffer.
This process should take about 7 to 10 days. Start by placing your begonias in a sheltered, shady spot outside for just two or three hours. Bring them back inside for the night. Each day, leave them out a little longer and expose them to slightly more light and wind.
- Days 1-3: Two to four hours in deep shade, protected from wind.
- Days 4-6: Six to eight hours in dappled light.
- Days 7-10: Full day outside, bringing them in only if a cold snap is predicted.
By the end of the week, the leaves will have thickened up. The plant will be adjusted to the natural movement of the air. This gradual move ensures that when you finally plant them in the ground or leave them on the patio, they won't wilt or lose leaves. For container-specific planting help, see our How to Plant Tuberous Begonias in Containers guide.
Choosing the Right Outdoor Spot
Once the timing is right, the location is the next piece of the puzzle. Begonias are famous for their love of shade. Most varieties, especially the large-flowered tuberous types like Picotee White, prefer filtered light or morning sun with afternoon shade.
If you plant them in a spot that gets hit by the hot 2:00 PM sun, the leaves can scorch. This is especially true when they are first moved outside. Look for a spot under high-canopy trees or on the north or east side of your home. A covered porch is often the perfect environment for Hanging Begonias in containers.
Good drainage is also essential. Begonias like to be moist but never soggy. If you are planting in the ground, ensure the soil is loose and rich in organic matter. If you are using pots, make sure they have plenty of drainage holes. This prevents water from sitting around the roots, which is the most common cause of plant stress.
What to Do if a Late Frost is Predicted
Even the best-laid plans can be interrupted by a surprise cold front. If you have already moved your begonias outside and the forecast suddenly calls for a drop in temperature, don't panic. You can easily protect your plants with a little bit of effort.
For begonias in containers, the easiest solution is to move them into a garage, shed, or back into the house for the night. If the pots are too heavy to move, you can cluster them together and cover them with a heavy blanket or a specialized frost cloth. If you are growing a moveable basket, Begonia Hanging Pink Balcony is a handy option to tuck away quickly.
For begonias planted in the garden, cover them with an upside-down bucket or a cloth. Avoid using plastic directly against the leaves, as it can trap cold and moisture. Remove the covers as soon as the sun comes up the next morning so the plants don't overheat.
What to Do Next:
- Check your local last frost date and add two weeks to it.
- Monitor nighttime temperatures until they stay above 55°F consistently.
- Begin the 10-day hardening off process for any begonias started indoors.
- Prepare your garden beds or containers with fresh, well-draining soil.
Signs Your Garden is Ready
Sometimes nature gives us better signals than a calendar. There are a few signs in the garden that suggest it is finally warm enough for begonias to move outside. When you see these signs, you can feel confident that the soil and air have reached the necessary warmth.
First, look at your lawn. When the grass is growing vigorously and needs frequent mowing, the soil is warming up. Second, look at other tropical-leaning plants. If your tomatoes or peppers are looking happy and green in the garden, the begonias will likely be happy too.
Finally, check the "weed" growth. While we don't usually like weeds, their active growth in the spring is a sign that the biological activity in the soil has begun. When the earth feels alive and the nights no longer have that sharp chill, it is time to bring out the begonias.
Specific Timing for Different Begonia Types
Not all begonias are exactly the same. While they all love warmth, some are a bit more rugged than others. Knowing which type you have can help you fine-tune your planting schedule.
Tuberous Begonias
These include popular varieties like the Non-Stop Begonias collection and 'Roseform' begonias. These are the most sensitive to cold. They have thick, succulent stems that hold a lot of water. If that water freezes, the stem cells burst and the plant collapses. Be very strict with the 60°F rule for these beauties.
Wax Begonias
Wax begonias are often used as bedding plants. They have smaller, waxy leaves and are a bit tougher. They can usually handle temperatures down to 50°F without much trouble. If you are eager to get started, you can often put wax begonias out a week or two before the tuberous varieties.
Rex and Foliage Begonias
These are grown for their stunning, colorful leaves rather than their flowers. Because their beauty is all in the foliage, you want to protect those leaves at all costs. Cold winds can tarnish the edges of Rex begonia leaves very quickly. Treat these like your tuberous begonias and wait for truly settled, warm weather.
Water and Fertilizer After Moving Outside
Once your begonias are in their outdoor home, their needs will change. Plants outside dry out much faster than plants kept in the house. The wind and sun pull moisture from the leaves and the soil.
Check the soil daily during the first two weeks. Stick your finger an inch into the soil. If it feels dry, give the plant a good drink. Avoid watering the leaves directly, especially in the evening. Water at the base of the plant to keep the foliage dry, which helps prevent mildew and rot. For a deeper look at watering, see our How Much Water Does a Begonia Plant Need guide.
After the plants have been outside for a few weeks and show new growth, you can start a regular feeding schedule. A balanced, water-soluble fertilizer used every two weeks will provide the nutrients they need to produce those spectacular blooms. Healthy, well-fed plants are more resilient to temperature swings.
Monitoring for Pests in the Spring
Moving plants outside introduces them to the local insect population. While begonias are generally quite healthy, spring is a busy time for many garden visitors. Keeping an eye on your plants during those first few weeks outside is a good habit.
Slugs and snails love the tender, succulent stems of begonias, especially when the weather is damp. If you see small holes in the leaves, look for silvery trails on the soil. You can manage this by keeping the area around your plants clear of debris or using a bird-safe slug bait.
Aphids can also occasionally appear on new, soft growth. A quick spray with a garden hose can often knock them off. Because you waited for warm weather to plant, your begonias will grow quickly. A fast-growing plant is much better at naturally resisting and outgrowing any minor pest issues.
Long-Term Planning for Begonia Health
If you get the timing right this year, you will be rewarded with blooms that last until the first frost of autumn. Tuberous begonias are wonderful because they don't have a "down" time. They just keep blooming as long as the weather stays warm and they have enough food and water. That is especially true with Upright Double Begonias.
As the summer winds down, you can start thinking about next year. In colder zones, you can lift the tubers and store them in a cool, dry place for the winter. This allows you to enjoy the same plants year after year. The tubers will actually get larger over time, producing even more flowers each season.
Getting the "when" right is the foundation of this cycle. By respecting the tropical nature of the plant, you set yourself up for a successful gardening experience. There is a great deal of satisfaction in watching a small tuber transform into a massive, flower-heavy plant because it was given the right start at the right time.
Caring for Begonias in High Heat
While we talk a lot about the cold, extreme heat is also something to watch for when you first move begonias outside. In some regions, spring can turn into a very hot summer almost overnight. If the temperature spikes into the 90s shortly after you plant, your begonias might need a little extra care.
Newly planted begonias haven't established a deep root system yet. In high heat, they can't always pull up water fast enough to keep their leaves from wilting. If a heatwave hits, you might need to water more frequently. You can also provide temporary shade with an umbrella or by moving pots into a deeper shade area until the heat passes. For more ideas on plants that thrive in shadier conditions, browse our Summer Flowers for Shade collection.
Most begonias will "rest" during the hottest part of the summer. They might produce fewer flowers when it is very hot. Don't worry; once the temperatures move back into the 70s and 80s, they will resume their heavy blooming.
Conclusion
Planting begonias outside is one of the most exciting moments of the spring gardening season. These plants offer a level of color and texture that is hard to match in shaded areas. By waiting for the soil to reach 60°F and ensuring nighttime temperatures stay above 50°F to 60°F, you give your plants the warm welcome they deserve. Remember that patience is a gardener’s best friend when it comes to tropical varieties.
We at Longfield Gardens are here to help you make your yard a place of beauty. Starting with high-quality tubers and following a careful schedule for moving them outdoors will lead to a garden you can be proud of all summer long.
- Wait for warm soil and nights above 60°F for the best results.
- Harden off indoor plants for 7 to 10 days to prevent shock.
- Choose a shaded spot with excellent drainage to prevent root rot.
- Keep a frost blanket handy for those unexpected spring cold snaps.
Gardening is a journey that rewards those who work with nature's timing. When you wait for the warmth, your begonias will reward you with a spectacular show that lasts for months.
FAQ
What happens if I plant begonias outside too early?
If begonias are exposed to frost, the leaves and stems will turn black and mushy, often killing the plant. Even if it doesn't freeze, temperatures below 40°F can stunt the plant's growth for the rest of the season. It is always better to wait for consistent warmth to ensure the plant stays healthy and vigorous.
Can I leave my begonias out if it rains heavily in the spring?
While begonias need water, heavy and consistent spring rains can be a problem if the soil doesn't drain quickly. Excessively wet, cold soil can cause the tubers to rot. If your area is experiencing a very rainy spring, it is often better to keep begonias in pots on a covered porch until the weather becomes more stable. For more container guidance, see our How to Plant Tuberous Begonias in Containers guide.
Do I need to fertilize my begonias as soon as I plant them outside?
It is best to wait until you see new growth before you start a regular fertilizer routine. This usually happens about two to three weeks after planting. For more care tips, see our Tips for Growing Tuberous Begonias guide.
Why are the leaves on my begonias turning yellow after I moved them outside?
Yellow leaves can be a sign of "transplant shock" or too much water. If you didn't harden the plants off gradually, the change in environment can stress the foliage. Make sure the soil is moist but not saturated, and ensure the plants are protected from direct, hot sunlight while they are still adjusting to being outdoors. For a step-by-step refresher, see our How Do You Plant Begonias: A Simple Step-by-Step Guide.