Abstract: In dicotyledonous plants, the direction in which the cotyledons unfold after germination is influenced by the orientation of the seed within the soil. Oriented sowing using seed trays allows for the control of seed orientation, thereby laying the foundation for standardised seedling cultivation, subsequent transplanting and grafting. Manual oriented sowing is labour-intensive, whilst existing oriented sowing equipment performs poorly in terms of both seed orientation accuracy and efficiency. In response to the agronomic requirements for the oriented sowing of pumpkin seeds in seedling trays—namely, that the seed apex must align with the centre of the seedling hole, the seed must be placed along its long axis, and it must lie horizontally at a 45° angle within the hole—this orientation ensures that the cotyledons unfold in the same direction with minimal mutual shading. Based on these agronomic requirements for seed orientation, a method for oriented sowing is proposed. This method employs a negative-pressure drum for seed supply, a suction nozzle for single-seed pickup, and a stepper motor to drive the rotation of the suction nozzle to achieve oriented sowing. A mechanical analysis of the seed capture process was conducted to establish the relationship between the adhesive force and the negative pressure and flow velocity, and the diameter of the suction nozzle tip was preliminarily determined based on the three-dimensional dimensions of the pumpkin seeds. To address the issue of unstable seed pickup at the suction orifice, the nozzle shape was optimised, resulting in cylindrical, conical and trapezoidal nozzles. The internal flow fields of these three nozzle types were analysed using Fluent simulation, and comparisons were made of the cross-sectional negative pressure and velocity distributions, as well as the pressure gradients on the seed surface, for seed adsorption by the different nozzles. The simulation results indicated that, under identical outlet negative pressure conditions, the conical nozzle exerted a stronger suction force on the seeds. The diameter at the tip of the nozzle is primarily influenced by the suction orifice cone angle and the suction orifice depth. A three-factor, three-level orthogonal experiment was conducted, with outlet flow rate, suction orifice cone angle and suction orifice depth serving as experimental factors. The main and secondary effects of each factor on the surface pressure gradient of pumpkin seeds were, in order: outlet flow rate, suction hole cone angle, and suction hole depth. Simulation results indicate that when the outlet flow rate of a single nozzle is 3.1×10^-4 m³/s, the nozzle cone angle is 30°, and the suction hole depth is 3.5 mm, the negative pressure gradient on the seed surface reaches its maximum value; this combination represents the optimal parameter set. A prototype for oriented sowing of processed seed trays was constructed, and seed pick-up and placement tests were conducted using a conical suction nozzle (with a suction hole cone angle θ of 30° and a suction hole depth h of 3.5 mm). Using seed pick-up success rate and seed loss rate as evaluation criteria, The results indicated that when the fan airflow was 5.5–5.75 m³/h, the sowing efficiency reached 290–295 trays/h, and the relative displacement of the seed from the centre of the suction hole on the drum was 0–4.5 mm, the nozzle’s seed pick-up success rate met the requirements for directional tray sowing. Based on these parameters, oriented tray sowing trials were conducted, yielding the following parameters for the oriented tray sowing prototype: a single-seed rate of 98% and an orientation success rate of 96.13%. These results provide a theoretical basis and design reference for the subsequent development of an oriented sowing scheme for pumpkin seeds.