Germination and seedling establishment for hydroponics: The benefit of slant boards

Abstract

Germination and seedling establishment for transplanting into hydroponics often uses porous substrates, but fine roots grow into these substrates, and they cannot be removed without damaging these roots. Seedlings transplanted without removal of substrates can cause interactions with solution chemistry or addition of particulates to the nutrient solution. Germination of seeds on slant boards is clean, uniform, and reduces the time to transplanting. Slant boards facilitate development of long roots, which maximize exposure of the primary root to the nutrient solution after transplanting. The "boards" are made from thin acrylic or polycarbonate sheets with germination paper on top. Seeds are held in place by covering with thin paper before vertical placement of the boards in the container. Four to twelve days later, the seedlings with long roots can be removed from the paper without damage and transplanted into the hydroponic system. Here we describe slant board construction and procedures for rapid germination and transplanting in hydroponics.

Fig 1. Side-view diagram of seedling transplanted into a hydroponic tank.

The root must be long enough to span the 1 cm air gap and have ample access to the solution immediately after transplanting.

Fig 2. Planting of lettuce (Latuca sativa) seeds on blue germination blotter paper.

Fig 3. Example of the growth of wheat roots through the thin absorbent paper.

It is difficult to separate the roots from the paper when this occurs. In this case, an additional piece of germination paper is recommended in place of the thin absorbent paper.

Fig 4. Acrylic holder for slant boards.

Fig 5. Germination slant boards under LED lights.

The photosynthetic photon flux density should be about 100 to 200 μmol m^-2 s^-1 to provide adequate light to reduce excessive hypocotyl extension.

Fig 6. Side view of cucumbers on slant board with an additional piece of germination paper on top of the thin absorbent paper.

Fig 7. Cucumber seedlings on a slant board with two layers of germination paper.

The roots of cucumber seedlings branch more than other species such as lettuce and tomato.

Fig 8. Neoprene cloning collar with lettuce seedling.

The top of the collar has been painted white to reduce light penetration into the nutrient solution, reduce temperature, and to reflect light back to leaves for maximum growth. A radial slit in the neoprene collar runs between the thumb and the plant.

Fig 9. Lettuce seedling in neoprene collar placed in rigid cover above nutrient solution surface about 7 days after transplanting.

Fig 10. Slant boards with germination blotter paper, lettuce seedlings, and thin paper over the seeds from day zero to day seven post seeding.

The thin paper can be removed to expose roots for inspection. Over-seeding helps for selection of uniform roots.

Fig 11. Example of rapid and excessive growth of lettuce (cv. Grand Rapids) and tomato (cv. Red Robin) roots over time.

Root elongation rate starts to decrease after roots are 20 to 30 mm long. Error bars represent standard deviation, n = 13. There is a large variability among seedlings. Overplanting by a factor of at least two allows for selection of the most vigorous seedlings.