The following information is an extension of our original germination guide. This is a technique pertaining to the maintenance of your seedlings once they have sprouted.
The Humidity Tent
In our original guide, we mention that we prefer to use small Chinese soup containers to germinate cactus seedlings. It turns out that the Chinese soup container is assistive to this technique. As many guides suggest, the seeds should be covered with clear plastic after sowing. Newly sown seeds need a combination of light, moisture and air. While clear plastic wrap works well, the opening of a quart-size zipper seal bag fits perfectly over top of the Chinese container. This gives you a perfect seal to lock moisture in while creating a pocket of air, so the seedlings have a little extra air to breath than with clear wrap pulled flatly over the top of the growing container. The pocket offers the added benefit of limiting the amount of condensation that forms. If you are already using a different type of container, the same type of scenario could be set up with a different bag, although it seems that the Chinese container and quart-sized bag were made for each other.
A simple compact fluorescent bulb is suitable for starting cacti seedlings for the first few months. But they key it to keep it right on top of the seedling containers. A small desk lamp with a bendable neck is ideal for directing the light at your seedlings at this close range. Eventually, you will want to move your seedling to stronger lights such as four-foot fluorescents or even HPS. If possible, you should look towards eventually moving your seedlings outdoors, if not just for the warmer months. It is important to realize that outdoor light is drastically stronger than even the best indoor lights, so you will have to start your seedlings out in complete shade and gradually expose them to more light. If the seedlings begin to turn red or purple, it is a sign that they are getting too much light.
Cactus seedlings enjoy water, and you should look to give them as much as possible without them rotting. So to avoid this you need to create a good enough supply of fresh air. You can accomplish this by venting. Venting does not occur continuously. It is part of a cycle. So you would start the cycle by having the humidity tent locked on tightly for a few days. Keep in mind that you should be keeping the soil moist. It should not be saturated, but moist like the tip of a new marker where the moisture is readily available but not ready to come out on its own. Now, if you were to leave the humidity tent on consistently, the air would stagnate and lead to mold. So this is where venting comes in. Venting simply means that you pull off one side of the opening of the bag. Due to the ideal fit between the Chinese container and the quart-sized bag, the opening is able to be a small slit such that you are literally able to create a vent while still having the tent largely in tact overhead. You can leave the tent in the vented position until the very top starts to dry out. After that, simply spray your soil back to its original moisture, put the tent back on tight and the cycle begins again!
*Maintain this cycle, transplanting at about 1 inch in height.
Humidity tent in the vented position
*TIP: As the seedlings grow, it is a good idea to put some loose cactus soil in between the seedlings to support them. Usually there will be about a centimeter or less of smooth growth at the base of the seedlings before the spines start forming. Sift out any larger particles in your soil, so it will fit between the seedlings easily, and sprinkle it between them until the soil level is about where the spines start to form. Always leave the tips above the soil of course. But once the spines start forming, you can bury the growth below to give extra support as the plant develops more.