The term “pricking out” may not be familiar to everyone. It is a step that is carried out every so often, depending on the plant.
“Pricking out” means separating seedlings growing together and transferring them to their own spot in the bed or pot. When many seeds are sown together in the same container, they gradually grow larger and larger until they become too dense, at which point it is time to prick them out. Read on to find out everything about this important gardening method.
What is pricking out?
In horticulture, pricking out is the process of separating seedlings or young plants that are growing too close together. During this process, weaker plants are usually also discarded.
The purpose of separating the small plants is to provide them with enough space to grow. As the seedlings grow larger, they begin competing with each other for water, light and nutrients. During pricking out, they are carefully removed from the substrate with an appropriate tool and transplanted at a greater distance from one another or into individual pots. In larger nurseries, this step is often considered too time-consuming, which is why they use specific seeds and sowing techniques to avoid pricking out. However, for hobby gardeners and in smaller nurseries, it is a common practice.
When to prick out seedlings
The optimal time for pricking out seedlings is when the plant’s cotyledon stage is complete and the first true pair of leaves is showing. By then, the seedlings have grown enough to cope with pricking out.
Instructions for pricking out plants
Pricking out requires some practice and finesse, as the seedlings are still very delicate and can break easily. You will also need a pricking out tool, but you can also use household items such as a small spoon. Here is our step-by-step guide of what to look out for and how to prick out seedlings:
- If transplanting seedlings into pots, fill the pots with some substrate and lightly press down. This ensures the seedlings can be placed in soil again as quickly as possible. Water both the substrate with the seedlings and the substrate in the new pots well before pricking out. This makes it easier to separate the seedlings and also helps them to adjust to the new environment.
- Now, take your pricking out tool and insert it into the substrate next to a seedling. Then carefully lift the plant out of the substrate from beneath the roots. While doing so, gently hold the plant close to the root neck − do not apply pressure or pull too hard. If the hypocotyl (the germination stem) breaks, regrowth is no longer possible.
- After removing a seedling from the substrate, make a hole in the soil of the new pot. Then, insert the roots of the seedling into this hole. If the root system, or the plant itself, is quite long, use the pricking out tool to carefully push it into the hole. It is beneficial for the growth of the seedling that the radicle (the embryotic root directly under the germination stem) is upright in the hole. Ensure the root neck is in the soil as well.
- Carefully press the soil around the seedling with your fingers to fill in the hole.
- Watering is an important step for the healthy rooting of the freshly pricked out seedlings − it restores the contact between substrate and roots. Water the pots either from below or above. If the substrate has already been watered in advance, this step is not necessary.
- Seedlings of different plants are often difficult to distinguish from one another, so be sure to label the pots to identify the species and variety. To reduce water stress on the seedling, a temporary cover can be placed over the plants. This will increase the humidity and protect the recently handled fine roots while they readjust.
Tip: Plants such as tomatoes can be planted deeply up to the cotyledons when pricking out, as they have the ability to form new roots on their stems. However, this phenomenon only occurs in some plants, so do your research for the seedlings you wish to transplant ahead of time.
The right tool for pricking out seedlings
The pricking out tool (dibber) is a plastic, wood or metal stick. It is about 18 centimetres long and tapers to a point. If you do not have a dibber, feel free to use a ballpoint pen, a wooden popsicle stick or a small spoon.
What soil is used after pricking out?
As the roots of the seedlings are still very delicate, use a low-nutrient seedling soil after pricking out. This ensures that the young plants become strong and robust and develop vigorous roots in their search for nutrients. A healthy root system also enables the plants to better nurture themselves later, for example during dry periods. We recommend transplanting the seedlings into our Plantura Organic Herb & Seedling Compost after pricking out. It has a loose and airy structure and is low in nutrients to help stimulate the root growth of young plants.
Some plants, such as tomatoes (Solanum lycopersicum) and peppers (Capsicum), require more nutrients than others. For such plants, it is indeed advisable to mix the seedling soil with a nutrient-rich soil to avoid undersupplying the young plants with their required nutrients. Of course, there are other plants with more specific soil requirements. Succulents, for example, need a mineral-rich substrate.
Which pots are suitable?
Which pot sizes to use when pricking out depends on various factors. These include how quickly the plant grows, how much space the plant requires, and how long the plant will stay in the pot. The number of seedlings can also play a role. If you are pricking out a lot of seedlings, it might be worth your while to use pricking out trays. When there are a smaller number of seedlings, they can be pricked out into one pot, as long as there is enough space for each one to continue growing.
Pricking out is a method that is often used, especially when growing tomatoes. Find out everything you need to know about pricking out and planting tomatoes in our specialised article.