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When growing from seed, there are a number of different growing mediums that we can use; Soil, Stonewool (Rockwool), Clay pellets & Vermiculite are all suitable growth mediums. Before we plant our seed we need to decide which medium best suits our purposes.

By and large, selecting the right growing medium is a matter of personal preference. When seeding, you should select the medium that best suits your needs, with foresight into what you expect to use later on in the process – i.e. if you plan to use stonewool for transplanting later on, then you should start with stonewool.

The size of your seeds plays a part in which medium you choose to use. For example, smaller seeds are likely to fall through clay pellets due to the exposed areas left in between each pellet. We want to get the most out of our seeds by giving them the best possible opportunity to successfully germinate and properly grow into well performing plants.

Best Practice For Planting Seeds In Soil

This is very easy, all you have to do is poke a hole in the soil, drop your seed in, cover the hole and wet the growing medium down. You want to make sure than the pointed end of the seed is laid flat, which is to say sideways. You don’t want the narrow pointed end of the seed pointing down into the growing medium, because that’s where the seed is going to actually germinate from upside down and start growing into the growing medium. You want the seed to lay flat or the rounded end to be pointing down. This allows the seed to follow gravity and have the root tip come out and head down into the growing medium.



When the roots grow and the seed starts to come out of the ground, the medium is moist so the seed shell is moistened and separates itself from the seedling as it grows toward the surface of the growing medium. The seed shell will brush against the growing medium trying to remove itself. If the seed shells do not come off when they reach the surface you can take a spray bottle and moisten the shell and release the seedling to open it up with your fingers, allowing the seedling leaves to open up and get into the light.



How can we tell if the soil has the right moisture for the seeds? That’s rather difficult because a lot of people plant their soil wrong. There are holes in the bottom of your growing chambers; they’re always supposed to be open to air. You pour your water over the growing medium and you want the water to flow out of the bottom. With hydroponic growing mediums, after a few hours the water will drain enough so that you have a good combination of water, air, nutrients and above all moisture. Soil takes longer, possibly up to two days. When we water soil, the soil particles are small and attract water creating a solid block of water through retention.

A good way to test the moisture level is to take a handful of soil and squeeze it after you’ve watered it. You don’t want excessive quantities of water dripping through your fingers. If this happens the soil is too wet. What you do want is a little water dripping from your hands; you also want the soil to retain the shape that you squeeze it into as the moisture binds it in place. Then, use a finger to lightly prod at it until it breaks apart.. If the sample is ‘powederising’ then your soil is way too dry. Conversely, if water drips from where you broke the soil then it is way too wet.



Why is water so integral to growing? Soil-less mediums have very little mineral elements available to them so the water is constantly delivering nutrition to plants. If we have too much water with nutrients delivered with no drying process the small particles in the soil will create a water tension that will become a solid block of water that your plants cannot breathe in. The seed pod has enough nutrition in it to facilitate it for six weeks of plant growth – but we want the plant to be up and growing faster and this is why we deliver water and nutrients trying to get a proper water to air ratio within the growing medium. Hydroponic growing mediums are very well suited to do this. Air/water/nutrients combination is at its peak within a few minutes of feeding.

Clay Pebbles

How does soil differ from planting in clay pebbles? There’s really no difference between the two growing mediums. Both act as anchorage for the root system of the plant. That’s why we use a growing medium; to give a seed the anchorage necessary to hold it upright, and at the same time separate the roots from each other. Plants adjust the pH of the growing medium to bring the mineral elements of the nutrients into a better relationship with the plant. Clay pellets are (as the names suggests) small, round balls of clay. They create very large openings through the growing medium, which means small seeds aren’t going to be able to anchor and they’re just going to fall to the bottom of your pot. To prevent this, a good practice is to use vermiculite to nest the seed securely in the clay pebbles.




Unlike most other growing mediums, it’s good practice to really soak stonewool before planting your seeds. Submerging the stonewool cube for at least ten minutes and then laying it out on the hills and valleys that are built into the stonewool tray will allow stonewool to drain to the proper level of water/air with nutrients. When using a stonewool cube, you will find that in the top there is already a hole available for planting your seeds. Once your seeds are happily nestled, tear a pinch of the stonewool off and plug the hole to cover your seeds.



What’s interesting about the manufacture of stonewool is the manner in which the fibers can be layered for different applications. Smaller cubes in flood and drain systems are layered vertically to allow the water to pass through the medium without disturbing its position. This allows water to be drawn to the top of the medium during flooding. Larger cubes or slabs used in drip systems are layered horizontally to spread the water evenly when it drips onto the stonewool growing medium. In both cases, the wool is designed to be successful at drawing up water and spreading it evenly throughout the medium. All growing medium are designed to anchor a seed and separate the roots from one another. When choosing a growth medium, make sure you maintain the proper pH.



Seeds are as varied as people in their characteristics. Accordingly, there aren’t universally applicable techniques which will definitely work for all seeds even though the basic process which seeds go through is the same throughout nature. As ever, trial and error are the best teachers for anyone seeking to learn what works best. Whilst it isn’t always possible, planting different types of seeds separately will make life a lot easier.

Smaller seeds can be exceptionally difficult to handle individually, and reasonably delicate to boot. In many cases your seeds might be better off lying closer to the surface of your chosen medium, rather than having been man handled into specific holes. In this case it’s best to be very wary when watering the medium before any greenery has started to show, because the seeds can easily be washed away if they have yet to anchor into place.



Some larger seeds, especially older ones, benefit from an overnight soaking in warm water. On more expensive seeds you can use paper towels to create a wet bed and place another sheet so that you can peel back the top sheet and examine the seeds. Also make sure that seeds are not touching in case mould gets established on some seeds. Once the growing tips break through the seed shell, transplant. Seedlings are delicate; the direct glare of an HID bulb will more than likely be too much for them. Seedlings grow well under CFL bulbs, but if you do have to use HID be sure to position your seedlings towards the edges of the bulb’s glare.



An increasingly large number of seeds are inert, or incapable of growth. Also, growing from seed is not easy, which is why nurseries tend to sell more juvenile plants than seeds. The rewards are, of course, tenfold when you actually manage it. If you are planning to start growing from seed, don’t get disheartened by your failures. Also with seeds there is less chance of bugs being introduced into gardens compared to cuttings or larger plants. Despite popular myth, people aren’t generally born with green fingers; they’re earned through season after season of trial and error.


  • - Moisture and warmth.
  • - Don’t let it get soggy either.
  • - Be wary when watering the medium as seeds can easily be washed away.
  • - Don’t let your growing medium dry out.
  • - Mist seedlings when needed.
  • - Keep room temperature between 70-80°



This article was originally published in Issue 004 of HYDROMAG (April – May 2013).

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