The Catalpa tree, often called the cigar tree or Indian bean tree due to its long, slender seed pods, is a striking addition to any landscape. Growing this deciduous species from seed requires attention to specific horticultural steps for success. The process begins not with planting, but with preparing the seeds to emerge from their natural resting state.
Preparing Catalpa Seeds for Sowing
The goal of pre-sowing treatment is to overcome seed dormancy. While some fresh Catalpa seeds may germinate easily, many benefit from a two-pronged approach that mimics natural processes. The first step involves scarification, which is the mechanical alteration of the hard seed coat to allow water absorption.
A simple method of scarification is to soak the seeds in warm water for 12 to 24 hours before planting. This softens the protective outer layer, signaling to the embryo that moisture is available for growth. Alternatively, gently nick the seed coat with a sharp blade or rub it lightly with fine-grit sandpaper, taking care not to damage the inner embryo.
For species like the Southern Catalpa (Catalpa bignonioides), a brief period of cold stratification can improve germination rates by simulating a short winter. Achieve this by placing soaked seeds in a moist medium, such as peat moss or sand, sealing them in a plastic bag, and refrigerating them for about three weeks prior to sowing. This cold, moist period helps break down chemical inhibitors within the seed.
The Step-by-Step Sowing Process
Once the seeds have been properly prepared, sow them in a suitable growing medium. The ideal timing is indoors in late winter or early spring, about 6 to 8 weeks before the last expected frost. This head start gives the seedlings valuable time to establish before they face outdoor conditions.
Use a well-draining seed starting mix or a blend of potting soil and perlite to prevent waterlogging and rot. Sow the seeds in small individual pots or a seed flat with adequate drainage holes. For the best root development, consider using deeper pots, as Catalpa trees naturally produce a long taproot.
The small, winged seeds should be planted very shallowly, covering them with only about 1/8 to 1/4 inch of soil. Planting too deeply can prevent the tiny sprout from reaching the surface before its stored energy is depleted. After sowing, gently mist the surface to settle the soil around the seed without washing it away.
Caring for New Seedlings
After sowing, maintaining a consistent and warm environment encourages successful germination. Place the containers in a warm area, ideally where temperatures remain around 70 to 75 degrees Fahrenheit. Covering the pots with a clear plastic dome or wrap helps maintain the high humidity needed for germination, but remove the cover immediately upon sprouting.
As soon as the first seedlings emerge, move them to a location with bright light to prevent them from becoming weak and leggy. If natural sunlight is insufficient, use fluorescent grow lights positioned a few inches above the plants for 14 to 16 hours per day. Keep the soil consistently moist, but not saturated, throughout this early growth stage to support the developing root system.
If multiple seeds were sown per container, thin the seedlings once they have developed their first set of true leaves, leaving only the strongest plant in each pot. When the seedlings reach a height of two to six inches, they are ready for acclimation before permanent transplanting. This process, known as hardening off, prepares the delicate indoor-grown plants for the rigors of the outdoor world.
Hardening off is a gradual process, typically taking 10 to 14 days, allowing the seedling’s cell structure to strengthen. Start by placing the pots outside in a sheltered, shady location for one to two hours during a calm, overcast day. Over the following days, incrementally increase the time they spend outdoors and their exposure to direct sunlight, wind, and temperature fluctuations. This slow introduction ensures the Catalpa seedling is robust enough to thrive once planted in its final location.