They look nice and healthy. I never had any luck with acorn to tree growth. Any pointers you can give?
Sure. The first place to start is containers. Trees typically grow long tap roots quickly. In regular containers, the tap root will circle or j-hook. The tree may look OK, but eventually root constriction will occur. So, if you are going to start trees from nuts in the winter like I do, you need specialized root pruning containers. This is not a single container, but a series of root pruning containers are required. Not only does this deal with circling and tap root issues, but it produces a very dense root system. The brand I use is Rootmaker. They were created by the guy who did much of the research on air pruning roots, Dr. Carl Whitcomb. There are now a number of competing brands that have different levels of effectiveness. Whatever brand you buy, read some Dr. Whitcomb's papers and make sure the containers you get support the underlying principles of an air pruning system.
The Dunstan chestnuts you see in the picture are in 18 cell Express Trays. These tiny cells air prune the tap root at about 4" causing early upstream secondary and tertiary root branching. These trees should stay in this size container for 12-16 weeks and are then transplanted to a larger size container. I like1 gal Rootbuilder II for the second stage.
You also need a well drained professional mix to grow trees. It needs to have a chunkiness to it. You don't want a mix like miracle grow that is designed to retain water. I've used both Promix Bx and Fafard 3B with good success.
Once you have containers identified, it is time to look at the specific nut or seed. Some oaks like all chestnuts require a period of cold stratification before planting. Other kinds of oaks do not and can germinate immediately.
Chestnuts require a period of 60 to 90 days of cold stratification. They are high in carbs and susceptible to mold as are some kinds of oak. It is best to get your nuts directly from the tree or immediately after they fall. They can quickly pick up mold spores if left on the ground. I first wash the nuts under running water to remove anything I can. Next, I hydrate them by putting them in a bowl of water for several hours or even over night. Any nut that floats is bad, discard it. I then separate the rest of the nuts into groups of 10 to 20. I put each group in a ziplock bag. They need moisture to stratify, but too much moisture encourages mold. I like to add a damp medium to the bag. I prefer long-fiber sphagnum. This has anti-fungal properties that helps keep mold at bay. It also holds water. I take a handful of it and soak it in water. I then squeeze as much water as I can by making a fist. I place the long-fiber sphagnum in with the nuts. I zip the bag half way closed and fold it in half. I place it in the vegetable crisper for whatever duration of cold stratification the particular nut requires.
The next issue most folks have is water. Avoid city water unless you have had a chemical analysis done and you really know what you are doing. The best thing you can do is collect rain water and use it. In the winter, I shovel snow into 5 gal buckets and bring it indoors and let it melt. Even more important is how frequently to water. You don't water these on a schedule or with a fixe amount of water like normal containers. These are extremely well drained. You soak them. You keep applying water until it is running out of the bottom holes of the cell or the lower side holes of the larger Rootbuilder II containers. You can't give them too much water, but you can give it to them too frequently. They need to dry out between watering. The best way to water is by weight. The container will be heavy when it is first watered and get light when it needs watering. If you ever see the leaves droop, you have probably gone a little too long without watering. The trees are trying to reduce transpiration. Water them ASAP.
The final thing is fertilizer. I won't use anything but Osmocote as a fertilizer when they are in the little cells. It is too easy to burn plants with direct fertilization. Osmocote is a slow release fertilizer that has much less chance of burning them.
Next is light an temperature. You don't need fancy grow lights. The lights I like best are plain old fluorescent shop lights. The important thing with lights is the output in lumens, not the color (temperature in K). Light intensity diminishes with the distance squared. So hot lights that might put out more energy must be kept further from the tree so more light is lost due to the distances. The cool shop lights need to be rigged so you can adjust the height as the trees grow. I like to keep them 2" - 4" above the trees.
You want to keep the temperature between 70 and 80 degrees. It is also best if you can keep a higher humidity but humidity is a second order factor at best.
That is pretty much the big picture. Using this kind of system, with a little luck, here is what you can end up with:
This Dunstan Chestnut tree was started under lights last winter. I transplanted it from an 18 to a 1 gal RB2 to a 3 gal RB2 in one growing season. This picture was taken on October 1st 2015 when I planted it in the field. For reference the tube is 5' tall. The tree is slightly over 6' tall and about 3/4" in caliper. Keep in mind that chestnuts are a pretty fast growing tree so not all kinds of trees will grow quite this quickly but it give you an idea of what is possible.