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DIY Hydroponics - Starting Seedlings

Starting seedlings for your hydroponic garden is easy and can be a rewarding experience. Although with my outdoor hydroponics I often cheat and buy punnets of seedlings from my local nursery there is a great deal of satisfaction in raising a plant from seed, nurturing it through its fragile early days and seeing it reach fruition as an adult plant. When you raise a plant from seed there is a certain degree of satisfaction as you eat its fruit or admire (or otherwise) its flowers because you grew it yourself.

What you need to start seedlings!Seedlings start best in my opinion in rockwool cubes however a 80/20 mix of perlite and vermiculite will give similar results. The rockwool has the advantage of not requiring a pot or container, it has excellent air/water retention properties and its cheap. Aside from the rockwool we will also require a watertight container such as an ice cream container and of course your chosen seed. Purpose made seedling trays are available if you would prefer one but the ice cream container is made of food grade plastic, is easy to clean and suits our DIY theme just fine. The scalpel is not necessary but makes cutting the rockwool cubes easier. The seed we are going to sow today is capsicum, a delicious and nutritious addition to the dinner table that grows well in most hydroponics systems.

Rockwool seedling or cutting cubesWhen you buy rockwool cubes for the nursery they generally come in slabs like the one we have pictured here. They are precut but the cut doesnt go all the way through so you can keep your seedlings or cuttings in one slab and divide them as necessary. If you keep the individual seedlings in one slab to start off with they will retain moisture far better than if cut into individuals. To germinate our seeds successfully we need two things above all others, warmth and moisture and keeping them in one block will give a reasonable advantage over seperating them.

Soak your RockwoolBefore planting our seed in the rockwool cubes it is a good idea to clean it first. Plants have been growing happily in dirt for years and are tolerant to bacteria but a modicum of hygiene can help to create a healthy garden. Rockwool cubes can also have salts and other undesirables from the manufacturing process. To loosen them up soak the rockwool cube for at least an hour in water (in your ice cream container) and then rinse them under a tap gently for a few minutes, allowing the water to flow through the cube. Place them where they can drain naturally and rinse your ice cream container thoroughly to remove any impurities that may have accumulated during the soaking. Most rockwool cubes have predrilled holes in the top of them but these are often not big enough for seeds. Enlarge them if necessary so that the hole is not too tight and the seedling will have room to move when it germinates.

Rockwool seedling or cutting cubesThe final remaining step is to place the seed into the hole in the rockwool cube gently so that it is about a millimetre below the top surface of the cube. Place the rockwool back into the ice cream container and fill the bottom with about 5-8mm of water so that the cubes are moistened. At this point the ice cream container, complete with freshly planted seeds, can be left in a warm place until they germinate if you so wish. If you intend to raise them in an indoor nursery in a cutting box you might prefer to move them directly into the nursery. If they are to be used for outdoor hydroponics it is best to keep them indoors at least until they germinate to ensure that the seeds arent carried off by hungry insects.

Our Hydroponic Seedlings have GerminatedAfter a week or so in our nursery our capsicum seedlings had started to germinate and as pictured they are ten days old (from planting). Our nutrient strength guide tells us that capsicums like a cF of about 18-22 however young seedlings will not appreciate full strength nutrient solution being applied to them after being germinated on plain water. When they first spread their first set of leaves it usually is a good idea to start them off on plain water and superthrive (1ml superthrive per litre of water) for a day or two. After that water them with half strength nutrient until they become more established, usually after three to five days they can be fed on full strength nutrient solution, though if the recommended strength for your chosen plant is 18-22 cF keep the nutrient at 18 rather than 22 for the first few days.

When the seedlings have developed several sets of leaves and the roots have started to grow out of the seedling cube they are ready to transplant into your main hydroponic system. You can follow the progress of our capsicums here by going to our Using a Top Feed Hydroponics System page.