Use the old solution to feed indoor and outdoor plants. Keep the reservoir full most of the time, but you can allow it to fall three to four days before time to change it. The best way to start seedlings is to sow seed in rock wool cubes or blocks, available at garden centers or hydroponic retail stores. Soak the cubes in water for 24 hours before sowing seeds to adjust the pH and thoroughly moisten the cubes. Buy seeds of varieties known to grow well hydroponically.
Seeds are available from hydroponic retail stores as well as many mail-order seed companies.
Sow lettuce seeds into 1-inch cubes and don't transplant them into blocks. Sow cucumber seeds directly into 3-inch blocks. Immediately upon germination, place the seedlings under light. Transplant herbs at a similar stage, but note that the time until true leaves appear may be considerably longer. European cucumbers take two to three weeks, and peppers take five to six weeks.