After sowing the adenium seeds, my arbitrary cut-off is two weeks--if seeds have not come up after two weeks, I consider the exercise to be over and done. At this point, you can remove the lid from your seedling container as well as the propagation mat, if you are using one.
|Adenium obesum seedlings, Week 3|
During the third week after germination, be careful not to overwater your seedlings (it's the leading cause of death among my other plant projects). I have no instinct for this so I judge it by weight. If the container is noticeably lighter, I water. If not, I struggle to walk away. At this point, I water them maybe once a week. It's easy to make that a regular thing because the temperature range is pretty constant, I keep the room at a constant humidity level of 50 percent and they are under artificial light 16 hours a day.
This is the only advantage of growing them indoors: you can control the key elements of healthy plant growth. The downside: you have to control the key elements of healthy growth.
Until temperatures go up to a minimum of 16C during the night, keep seedlings indoors under artificial light if you do not have a sufficiently sunny spot. Once outdoor temperatures go up, they can be gradually introduced to direct sunlight.
|Adenium obesum, Week 5|
Most experienced growers advise against fertilizing until they are at least a year old and I agree with this. Fertilizing seedlings does accelerate growth but you might not get the shape you want. The plant might also be weaker going into the following winter so if you do decide to fertilize your seedlings early on, take note to stop early in autumn to give them time to harden off before the cold season.
So I do not fertilize my seedlings since I prefer them to be short and compact, like this.
Also at this point, I picked one of the seedlings to experiment on and pinched it. It is the only seedlings that has not indicated any intention of branching yet. The one pictured above, you can tell there are nodes for the next sets of leaves and those nodes are going to be branches. The one I picked is a straight, no-nonsense one. So I forced some nonsense into it. I don't have long fingernails so I used a box cutter to slice the top off where a new pair of leaves were starting. I probably should have sterilized the cutter before doing that. Didn't occur to me.
|7-month old seedlings in gritty mix.|
There is really no limit to the interesting experiments you can do with adenium seedlings, short of chopping them up and tossing them into a sauce pan.
Caring for Seedlings, Optimising Growth
Different plant cultures produce different results. For instance, the photo below shows the difference between basic care and growing hard. Just to confuse matters, sometines you get seeds that are just ridiculously awesome to start with, no matter what care you give it.
|From left. Six-month old seedling, given normal care; 2.5-year old plant, also given normal care; another 2.5-year old, grown very hard.|
Soil: If you want to optimise growth, I recommend keeping your seedlings in 50 percent potting soil (I prefer peatless) and 50 percent perlite. To achieve optimum growth in soil-free substrate like the gritty mix, or even its 5:1:1 version, it will just take too much effort to meet their water needs while growing rapidly.
Sun: As much as you can provide as long as you phase them in.
Watering: Learn how to tell if it is time to water. Water only when the pot is really light, indicating that the soil is dry. In my climate, this usually takes only 3 to 4 days because seedlings are voracious things. It will take longer to dry if the seedling is in a bigger pot than it needs (this is why seedlings should not be over-potted, too wet too long makes them rot-prone).
Moisture meters are bollocks so I don't bother with them. Instead, do this: water your plant. Then lift it with both hands. That's how it feels when it is wet. Check after a week and see how much it weighs in comparison. It should be dry by then. Now you have an idea what dry feels. Water the plant when you get at or close to that point. If you have six thousand pots, goodluck.
Fortunately, you really only need to do this benchmarking in the beginning. Eventually you develop a sense of how fast your plants take up water and how fast your climate evaporates moisture in your potted plants. If, after a week, your pots still weigh as much as they did when you watered, your soil is probably not drying fast enough. I'd recommend amending to kick that up a notch.
Feeding: There are different schools of thought on this subject. Some growers do not fertilize until after a year and some never stop fertilizing weakly, weekly. If you prefer short, compact plants, fertilizing weakly weekly is your best bet. Keeping the plant barely but consistently nourished will reduce the odds of dramatic growth spurts that turns young plants into tall, formless things.
Keep an eye on how seedlings adjust to fertilizers. Lack of nutrients usually shows up on the seedlings as gradual yellowing of leaves, even new growth. If the soil is dry, water lightly before you apply water with fertilizer.
Picking what fertilizer to use is also tricky and fraught with myths and tales. Just remember that plants need more than just nitrogen, phosphate and potassium. They also need trace minerals in the amounts naturally found in the soil. The easiest way to do this is to use a fertilizer mix with trace minerals already in it. An even easier way is to remember the rule "feed weakly, weekly". Weakly means mix half the recommended dose every week.
Winter: Adenium seedlings less than a year old usually do not go dormant. Bring them indoors as soon as night temperatures go down to 16C. They can be kept on a window sill if it is facing south or lit with artificial lights. Do not feed them unless the tips of the leaves start turning yellow. Keeping them fed in the winter will push growth but it will be weak and, without adequate light, etiolated.
Moving Seedlings Outdoors Further north of the equator, adeniums have been known to do fine outdoors with night temperatures dipping below 10C. As a general rule, though, you're better off waiting until night temperatures go up to an average of 16C. During the first week, keep the seedlings in the bright shade. After that, look for a spot with dappled shade and let them stay there for another week, gradually moving them into direct sunlight. First, let the seedlings get morning sun and after a week of that, they can manage as much sun as you can provide.
Repotting: Seedlings can be kept in the crib where they germinated for as long as you want. There is no need to repot them until you notice that you are watering at twice the rate that you used to.
Pests: Infestations of any kind usually shows up as malformations on the leaves of young seedlings (and adults). Caterpillars could be chewing on old leaves or mites could be eating young shoots. Either way, a good and thorough spray of horticultural oil, neem spray or even just a dilute solution of alcohol (half and half) will normally resolve it.
Spray all parts of the plants above the soil and then spray the top of the soil, then spray the pot itself. Hell, spray the bench, as long as you're at it. Do this only at sundown---a sprayed plant will burn in direct sun. Repeat this process every three days for at least a week or more if you are extra-paranoid or if you see persistent infestation.
Soil-dwelling pests can be treated with Bacillus thuringiensis, usually sold in granule form and mixed with water. Drench the soil with this and repeat next time you have to water the seedlings.
Done properly, spraying works extremely well and there is rarely a need for systemic pesticides.
Next: Part IV: Repotting seedlings
Previous Post: Part III Germination
Update: One year later
Related Post: Part VI: Pruning Adenium Seedlings