Tips for growing great vegetable and herb seedlings
We grow thousands of plants from seed every year to grow out in our market garden, seed farm and for sale. Over the years we have tried many different seed raising mixes and containers to grow in. We have tried many different commercial seed raising mixes but have found our own mixes to be far superior. We used to use very complex mixes with many different ingredients but over the years have simplified and mix down to three ingredients; equal parts good quality compost and vermiculite for the body and about 2 percent Blood and Bone for the fertility. We use this mix for pretty much every type of seedling we grow from Amaranth to Zucchinis.
You might regularly read on other blogs to use a sterile seed raising mix to ensure disease free seedlings, I believe this is a mistake. Modern research has shown that interactions between micro-organisms in the soil and plant growth are extremely important for the vitality of the plants. By growing in a sterile medium you deny those seedlings these extremely important interactions. We prefer to use a living compost in our seed raising mix to get the seedlings used to interacting with micro-organisms. Also, it's those micro-organisms which breakdown the blood and bone fertilizer we use to make it available to the seedlings. Yes, occasionally we get a batch of mix or the right environmental conditions where the ‘bad’ microbes are in excess and we lose some plants. However, this is not necessarily a bad thing, as this itself can act as a part of our selection process ensuring the next generation of those plants are more resistant to those pathogens.
We have also tried many of the different seedling containers on the market as well as biodegradable products with Jiffy pots and no pots at all, as with soil blocks. Biodegradable pots and soil blocks are great as you do not have to disrupt the roots as much when planting. The roots grow out to the edge of the seed raising mix, then when they come in contact with the air they pause their growth. When they are planted in the soil they resume growth straight out into the soil. This leads to a more natural root form and eventually a healthier plant. Their downside is that they require more observation when watering as they can dry out from all sides, not just the top. Plastic pots and punnets work well, especially when growing larger numbers of seedlings. Their downside is that seedlings grown in them tend to become much more root bound than biodegradable pots and the roots are disturbed much more when planting out. This can contribute to what is referred to as transplant shock and set the plant back quite a bit. The single most important lesson we have learnt when growing seedlings in pots is to always grow seedlings in the biggest container practical (but still appropriate for the type of plant). There is always a trade-off between this and available space, but we have consistently found the bigger the container, the faster growing and healthier the plant is and the more it producers.
In addition to the soil mix and container choice, the other important factor in growing great seedlings (or more importantly great plants from those seedlings), is planting them out at the right time. People often mistakenly see large leafy seedlings in garden stores and think that means the seedling will do better when planted out in the garden. In actual fact it is usually the exact opposite of this. Usually their seedlings have been in the punnets for far too long waiting around on the shelf for someone to buy them. The earlier a plant is placed in its final growing space the better that plant will grow. Punnets with large leafy seedlings above ground tend to have stunted or rootbound roots below ground. Also, older seedlings are far more likely to suffer from transplant shock and will want to bolt when they are planted out. The correct time to plant out a seedling is as soon as it is large enough to easily be handled and removed from it's container.
How do you grow yours seedlings? Do you have a secret soil recipe or great tips to share? Let us know in the comments below, we would love to hear from you.