How to Choose Soil for Spring Transplants
Updated: Feb 13, 2018
Fine, uniform, aerated, loose soil helps regulate the environmental factors that contribute to healthy seed germination, and allow you to achieve consistent results in your garden.
When you’re preparing your Spring Transplants, it’s a small amount of soil you’re starting with, so big chunks of bark found in a less uniform soil can obstruct roots from, well... taking root!
Coconut coir is a material I like to teach people about when they’re starting their seeds because it’s beneficial in so many ways.
This ground-up coconut husk comes in a tightly packed cube; you add water to it and it expands quite a lot.
When you break it up, you can see it’s very uniform, which is ideal for fostering successful seedlings.
People used to commonly use Peat Moss, which is an ancient decomposed material that is not a renewable resource – they mine it out of bogs, and it is used up. The environmental impact of using Peat Moss is more significant than coconut coir, which is a byproduct of the existing coconut industry, making coconut coir a sustainable choice for your garden.
There are other products you can buy like Seedling Mix, which incorporates Perlite, a mineral that is heated until it puffs up kind of like popcorn.
These small white pieces in the mix are added for drainage. For small projects, just buying a bag of Seedling Mix could be a good way to go.
Seedling Mix is different than Potting Soil or Compost because Seedling Mix, just like Coconut Coir, is sterile. It’s important to create what we would consider a “low fertility,” sterile environment, which is less likely to have pathenogenic organisms that cause disease in young, germinating plants.
Richard Job, a guest at my Spring Transplants workshop, responded to this with the following observation:
“So, I’m imagining there are no nutrients in Coconut Coir and Seedling Mix.”
… and Richard is right – there aren’t any nutrients available in this sterile environment. At first, everything this germinating plant needs, it gets right there within the endosperm of the seed. But once the seed starts to get “True Leaves”, at that point it does need some nutrients.
First Leaves (Cotyledon), and True Leaves
Cotyledon are the first leaves to sprout from your seedlings.
These “First Leaves” look different than the True Leaves that come out later. They’re usually sort of smooth and simple and smaller than True Leaves. The First Leaves give the plant the opportunity to reach out and begin photosynthesis, then it starts craving the carbohydrates that photosynthesis produces inspiring the seed to put out its True Leaves. This is when your transplants start to display their identity. You’ll see that True Leaves look more like the traditional … tomato leaves, for example.
Once the plant has True Leaves, it will need some nutrients. A good way to give your seedlings what they need when they’re getting established is organic liquid fertilizers.
Although potting soil may have nutrients a plant needs, it will also have some organisms that could end up attacking the plant when it is still too young to protect itself. So, a combination of Coconut Coir or Seedling Mix, and an Organic Liquid Fertilizer works well for the development of your transplants.
You may be looking at your planting tray and wondering if the Cotyledon (first leaves) and true leaves can develop in such a tiny space. They will. In fact, each plant will develop Cotyledon, and true leaves, and another set of true leaves – maybe three or four sets of true leaves before you are up-potting.
One way to tell if you’re ready to move your transplant to a larger pot is to lift up the tray and check if you have roots coming out of the bottom. Ultimately, all those roots will fill up this small space, and start growing through the holes at the base of your planting tray. You can even press underneath the tray and pop the plant out to see if it’s getting close. If it comes out as one big clump – it’s clear it’s time to up-pot. At that point you’ll use a more traditional Potting Soil.
You can use Seedling Mix or Coconut Coir all the way up to the point when you’re ready to up-pot, or even put that transplant directly into your garden. And don’t worry, your spring transplants will do fine in that transition from the sterile environment into potting soil … or right into your garden if the ideal planting temperature is upon us.