How to Grow Rex Begonias

Rex begonias can be very demanding of just the right amount of water, food, and humidity. Plants will vary and the only way to know what your plant wants is to watch it, once it has adjusted to its new surrounding. If it’s flourishing, continue with what you were doing. If it is droopy or gangly, adjust the light and water. Eventually, you’ll figure out the right balance.

Be sure your garden beds or containers meet the requirements of the rex begonia. Alternatively, if your area is too cold, consider growing yours as a houseplant or in an outdoor container that can be brought indoors in cooler weather.
Light

Full sun to partial shade. Avoid direct sunlight. They need some light to keep their coloring, but bright, indirect light is best.
Soil

Rex begonias prefer light, rich soil. When planting directly in the ground, a moist, well-drained location is optimal and mulch will keep the roots shaded. In pots, be sure to provide drainage holes. A peat-based potting mix is ideal for containers.
Water

Begonia rex should be watered when the soil or pot feels dry, but don’t wait until the plant starts to wilt. You can cut back on water during their dormant period in the winter, watering only when the pot dries out. Humidity is crucial to keeping your rex begonia happy, however, spraying the leaves can lead to spotting. It’s better to cluster your plants, so they can create their own humid environment, or use a pebble tray.
Temperature and Humidity

Begonia rex is sensitive to temperature changes and to temperatures below about 60 degrees Fahrenheit (16 Celsius). You can keep them happy as houseplants or store them dormant over winter, as you would with other tender bulbs. These plants do require high humidity (more than 50 percent), which means it can be difficult to maintain rex begonias indoors over the winter.
Fertilizer

You can feed your potted plants monthly with any good houseplant food. Too much food will make for a scraggly plant, so pay attention and adjust the feeding to suit your variety. Rex begonias can be temperamental and you just have to find the right conditions and balance for your plant. Don’t feed at all during the winter.
Potting and Repotting

Repotting rex begonias each spring will ensure that they have plenty of soil to grow in, but they like to be a little bit pot bound. Large or gangly plants can be pruned into shape. Rotating potted rex begonias will keep the plants full and stocky