To begin, prepare your sponge. If you are going to use a natural, biodegradable sea sponge, there really isn’t much you need to do aside from cutting it down to the size you want. These are great for growing herbs, and make the transplanting process extremely easy, as all you have to do is plant the sponge into the soil along with the plants. If you are using a synthetic sponge that has been used before, make sure you rinse it in hot water for around five minutes, squeezing and washing thoroughly, to get rid of any chemical residue. Then, leave it out to dry overnight.
Now that you have your sponge prepared, place it in a dish, and water it gently until it is just damp – you do not want the sponge to be soaking wet, so if you pour on too much, wring the excess out. Once this is done, sprinkle herb seeds onto the top of the sponge – around 15 to 30 should be fine, depending on the size of the sponge. Then, use your fingers to press these seeds into the pores of the sponge.
Set the dish containing the seeded sponge in a warm, sunny spot in your home, like a window sill. The sponge now needs to be treated much like a plant – make sure it gets plenty of sunlight, and is kept damp. The sponge cannot be watered directly as this might dislodge the seeds, so try pouring small amounts of water into the dish, and allow the sponge to soak this up on its own. Make sure it stays damp, but do not drown it in water.
Once the plants begin to sprout, grow at least 2 inches tall, and grow three to four leaf clusters, you are ready to transplant them into either a pot, or an outdoor garden, as per your preferences. If it is a synthetic sponge, it would be best to gently pull the herb plants out and then plant them. If it is a natural sea sponge, however, the entire sponge can be planted directly into the soil. If you wish to plant the herbs growing in the sea sponge individually, you can also cut the sponge up (make sure you do not damage any roots), and plant individual herb sprouts in the soil.