While the easiest way to produce seedlings is to grow them in a STYROFOAM SEEDLING BOX or similar large box seedlings that do not like having their roots disturbed do better when grown in single cell seedling trays. This page explains how best to use these trays.
Single cell seedling trays are ideal for growing seedlings that do not transplant easily, examples of such seedlings include, corn, pumpkin, zucchini and cucumber. They do not transplant easily as they respond poorly to having their roots disturbed. As the root structures of the seedlings in a single cell seedling tray are separated from other seedlings they encounter much less root disturbance when transplanted than seedlings grown in multi seedling punnets or seedling boxes.
Single cell seedling trays can also be artificially heated using a seedling heat mat or an AQUARIUM HEATER SEEDLING PROPAGATION BOX, whereas styrofoam seedling boxes cannot be artificially heated.
Single cell seedling tray cells vary in size. Larger cells can hold seedlings for longer than smaller ones, but whatever size cells you use it is best to wait until the seedling is root bound before removing it. Root bound seedlings are more likely to come out of their cells with their roots intact than seedlings that are not rootbound.
Single cell seedling trays readily available at retail nursery outlets (Australia). LEFT: Yates 48 cell tray. CENTRE: Saxon 24 tray. RIGHT: Reko 30 cell tray. The Yates and Reko seedling trays fit in standard 350 mm seedling trays (used to provide extra support) while the Saxon seedling trays fit the Saxon Mini Greenhouse.
As the seed raising mixture that each seedling is grown in is small in volume seedlings grown in single cell seedling trays are more prone to drying out or exhausting the available nutrients. As a result, seedlings grown in single cell seedling trays require more frequent watering and regular applications of diluted liquid fertiliser if they are to thrive.
As seeds contain all the energy they require to sustain life in the first few days of growth there is no need to add liquid fertiliser until they reach the dicot (two leaf stage), in fact applying too much fertiliser can burn or even kill growing seedlings.
As newly emerged seedlings are small they only need a small amount of water. But as they get bigger they will need more water and regular applications of half strength diluted liquid fertiliser as their nutrient requirements increase. When the seedlings are approaching maturity they will need full strength diluted liquid fertiliser to meet their ever-increasing nutritional demands. Though at any stage of the seedlings’ growth it is important not to overwater them. Overwatering single cell seedling trays runs the risk of leaching the nutrients out of the soil, especially when applying water that does not have any liquid fertiliser added to it. Seedlings grown in soil with the nutrients leached out of it are likely to be sickly and stunted
Seedlings grow better when fed with liquid fertiliser, but it is important not to give them too much fertiliser as this can burn or even kill the growing seedling. Water with clean water until the emerging seeds have reached the dicot (two leaf stage) then apply a half strength diluted liquid fertiliser until they are three quarters grown, followed with full strength diluted liquid fertiliser until they are ready to be transplanted. Apply only enough water/liquid fertilser to keep the soil damp.
Overwatering single cell seedling trays runs the risk of leaching the nutrients out of the soil, especially if you use water that does not have any liquid fertiliser added to it.
Seedlings grown in single cell seedling trays need to have grown big enough to have become rootbound before being transplanted. Removing seedlings when still small runs the risk of them not coming out of their cells cleanly, which will likely damage their roots.
To remove a seedling use your finger to depress the flexible bottom of the seedling tray while at the same time gently pulling the seedling from the top.
Once planted in the ground water the roots and the leaves with a diluted liquid fertiliser. The leaves are watered as well as they can also absorb nutrients.
Seedlings grown in single cell seedling trays need to have grown big enough to have become rootbound before being transplanted. Removing the seedlings when still small runs the risk of them not coming out of their cells cleanly, which will likely damage their roots.
A big advantage of growing seedlings in single sell seedling trays is that they can be artificially heated. These capsicum and eggplant seedlings are being grown in an AQUARIUM HEATER SEEDLING PROPAGATION BOX.
Corn and pumpkin seedlings grown in single cell seedling trays. Corn and pumpkin seedlings do not transplant well when their roots are disturbed. For a list of seedlings that do not transplant well when their roots are disturbed see the SEEDLING PLANTING SUITABILITY CHART.
Even seedlings of vegetables that do transplant easily, such as tomato plants, will transplant more easily when grown in single cell seedling trays.