If a space contains particularly poor soil, especially sandy, rocky, dry, or close enough to the coast to suffer from high salt levels, selecting the blackjack oak for the spot might make sense. A few things need to be considered about this oak species when deciding on a blackjack. While it might not reach 100 feet, it can still be an unmanageable space for a small area, reaching heights of 50 feet or so at times. Another consideration people overlook is that blackjacks do not have the same noble form as most oaks. The blackjack oak is not a stately tree; it is a bit of a scraggly ugly duckling but does possess the attractive ecological feature oaks are known for; it is a pollinator haven. If you are looking for a medium to a large tree for a landscape with poor soil and great ecological value, then the blackjack oak is one to consider. This oak species, while known to be unattractive and able to grow anywhere, can have its image improved with some tender loving care. The blackjack will grow in terrible soil and less than ideal conditions, but the tree will be a little rough around the edges. Luckily all the information you need to give your tree its best life is right here.
Light
Blackjack oaks are often found in the understory in nature, so unlike most oaks that require full sun that comes with being a canopy tree, these smaller species are used to receiving less light. Making sure a blackjack oak gets partial sun will ensure the tree gets adequate sunlight to grow at a healthy rate. Placing a tree in an area that gets too much sun or in an area that at one point had tree cover removed to allow the blackjack to receive more light will cause some maintenance issues in the long run. As the tree is exposed to more light, its limbs will grow outwards, requiring more frequent pruning, which is just extra work that can be avoided if the right site is chosen.
Soil
When caring for blackjack oak, soil quality will not be detrimental to the health and wellbeing of the tree. This oak species is incredibly adaptable regarding soil type and consistency and will do well in any soil, be it gravelly, sandy, sandy loam, medium loam, clay loam, or clay. What soil consistency determines is the tree’s aesthetic and how scrubby the appearance of a blackjack oak ends up as it grows into a mature tree. If given rich soil with plenty of nutrients and adequate moisture, it will grow into a tree more similar, not exactly like the oaks you are used to. The only caveats to this super-adaptability are its ability to withstand poor, overly wet soils and its preference for acidic soils. Fulfill these needs, and the tree will be happy and healthy.
Water
Another appealing aspect of the blackjack oak is its relatively low water demand. It is extremely drought tolerant and can do well in dryer areas that tend to dry out in between supplemental watering as it matures. Ideally, it should be watered as one would water any other newly planted tree until it is established five gallons of water per inch of trunk diameter during the first two growing seasons. Once it is established, let nature take over and handle the irrigation even during dry spells, the blackjack oak can handle it. The one thing that this tree cannot tolerate is overwatering or poor drainage.
Temperature and Humidity
Blackjack oaks have a large native range that stretches across a large swath of area in the United States from Texas to Long Island to the Midwest. It can handle warm summers but does not do well in humid areas faring best in coastal forests and semi-savanna areas. The USDA recommends zones 6 to 9, the blackjack oak.
Fertilizer
Depending on the soil the blackjack oak is living in can determine whether or not your tree needs the helping hand of fertilizer. As mentioned, this tree can deal with some pretty poor soil but can benefit a great deal cosmetically if the soil is more nutrient-rich. The first step in deciding if supplemental fertilizer needs to be added to the soil is to test it to decide if it’s deficient in nutrients and, if so, what. This is easy enough to do, most extension services offer tests, or there are plenty of tests available that are simple to use. Once known, the decision can be made if the aesthetic value of the tree is important enough to add some fertilizer or if the natural shape is perfect for the landscape design you are trying to achieve.
Types of Blackjack Oaks
The blackjack oak is not a horticulturally valuable tree to the nursery trade and therefore does not have any cultivars available. In the western edge of the blackjack oak’s range a variety of the species is prevalent, which is smaller and more scrubby in a form known as Quercus marilandica Münchhausen var. ashei. This variety is less attractive than Quercus marilandica and is rarely considered for horticultural use.
Pruning
Like any tree, the blackjack oak will require pruning. No surprises here for weekend warriors. This is where most of the care this tree requires will come from. Luckily, its natural form as an ugly duckling gives caretakers an excuse to be somewhat less formal with their shaping if they want to maintain a more natural look. If a more formal aesthetic is desired, prepare the tools. You can use a pair of pruners with a small young tree, but loppers or a pruning saw will be needed as the tree gets older. Be sure to clean the tools thoroughly with bleach diluted with ten parts of water in between plants, and after you are finished, this is especially important for oak species. Now that the tools are set, the first pruning should be done the first or second season after planting to establish a good structure. Cut any branches that intersect or point inwards. The purpose is to make the tree establish a form that flows upwards and outwards. Do this year every year in the early winter once the tree is dormant. As the tree matures, besides focusing on the firm also looks to remove dead, dying, or damaged branches. Suppose branches look as if they are diseased; call an arborist as numerous issues can plague oaks that should be kept ahead. When the tree becomes large enough, a ladder is required to prune; that is another time to give your friendly certified arborist a call.
Propagating Blackjack Oaks
Normally oak trees are propagated from acorns and done so somewhat reliably. Blackjack oaks are notoriously difficult to propagate from an acorn, making it necessary to attempt propagation from cuttings. Unfortunately, propagation of oaks from cuttings is also difficult, but it can be done. To be successful, the best step would be to take a cutting in the late summer. Use sharp, sanitized shears to make an angled cut below a leaf node or bud. Take a few cuttings to make sure some succeed. The cuttings should be six to eight inches. Remove any new growth from the tip of your cuttings. Fill a shallow tray about four inches deep with drainage holes with wet perlite and poke holes for each cutting. Dip each cutting into the rooting hormone, push into the perlite, and press it firmly down, ensuring it contacts the cuttings. Keep the tray in a cool area and maintain the perlite moisture until the next spring. At this point, if any of the cuttings develop new growth, new roots will certainly have formed. Be very careful with the new plants. The best bet is to take them into a shaded area following the last frost to harden off and slowly separate them at the one-year mark.
Common Pests & Plant Diseases
Like most oaks, the blackjack oak is plagued by numerous diseases like oak leaf blister and oak leaf wilt, powdery mildew, and canker. Canker, in some cases, is considered beneficial. Most of these diseases are not fatal if a tree is infected, but one is extremely problematic. Easily the most concerning disease is Oak Wilt, and sadly the blackjack oak is highly susceptibly to this fungal disease. Beetles transmit the disease, and when you notice the symptoms in the species, leaves yellowing and wilting, it is already too late. While beetles are the vector that causes oak wilt, most insects that inhabit the blackjack oak are beneficial as they are hosts for numerous pollinators, with the majority of the insects hosted by the blackjack oak either being little threat to the health of the tree or practical risk assessment of insects difficult and may be best done by a certified arborist.
Common Problems With Blackjack Oaks
Blackjack oaks do have some issues, but they are not issues that are the type that would dissuade someone from adding them to their landscape. The tree is vastly underutilized and has faced eradication in the wild in favor of more profitable timber wood. Its reputation as scrub wood makes it have the bad name of only being good for firewood, but it has much more value. In numerous states, it is rare or concerned conservation status, and without it being widely available in the nursery trade, it is not spreading to new locations.
