Acer RUBRUM

Acer RUBRUM - Red maple, scarlet maple, swamp maple, Red Maple.

Can be grown in bonsai style!

Acer is a genus of deciduous trees and shrubs in the soapberry family (Sapindaceae), comprising more than 120 species and numerous ornamental forms. Native ranges span Europe, Asia, and North America, with the greatest species diversity occurring in eastern Asia. Maples are found in mixed forests, on mountain slopes, in river valleys, and in parkland landscapes. The second genus in the subfamily - Dipteronia - is distributed only in China.

The plants have a rounded or broad, dense crown and large palmately lobed leaves with radiant venation. In autumn, the leaf blades take on brilliant shades of yellow, orange, purple, or reddish-brown, making maples among the most ornamental trees of the temperate zone. Shoots are usually light-colored, with varying bark hues on young growth.

The flowers are small, yellow-green, gathered in loose inflorescences and appear in early spring - simultaneously with the leaves or slightly earlier. The fruit is a double samara consisting of two winged seeds that separate upon maturity and are dispersed by the wind. The root system is predominantly shallow, which facilitates establishment but makes the plant sensitive to soil compaction.

Maple reproduces by seeds and suckers. Most species are light-demanding, tolerate urban conditions well, and are characterized by longevity: the average lifespan is 150-200 years, with individual specimens capable of reaching 300-500 years of age. Thanks to their ornamental appeal and hardiness, the genus is widely used in landscape gardening worldwide.

Red maple is a vigorous deciduous tree 12-18 m (39-59 ft) in height, forming a broad rounded or ovate crown. The leaves are 3-5-lobed, rich green above, grayish-greenish beneath, with conspicuous marginal serrations. Young shoots are reddish, which is characteristic of the species. In autumn, the tree becomes one of the most vivid among North American maples: the foliage turns fiery red, crimson, purple, and orange shades, often transitioning from one part of the crown to another.

Blooming occurs in early spring, before the leaves expand. The flowers are small, red or reddish-yellow, gathered in compact clusters and give the tree a noticeable "coloring" effect. The fruits are paired samaras ripening in summer; their wings often have a pinkish or red tint, rendering the tree ornamental even after flowering.

Maple seeds are samaras about 1-1.5 cm (0.4-0.6 in) long, ripening across different seasons. Most species, even under optimal conditions, have a natural germination rate of 20-50%. Simply remaining in the soil, they may germinate only after years.

Scarification significantly increases germination capacity and seed swelling; without disrupting the outer coat, germination will be minimal. The outer seed coat is carefully filed or nicked with a hard tool without damaging the embryo, after which seeds are soaked for 12-24 hours in warm water with the addition of stimulants (SUPERthrive, HB-101, Aminozol, Epin, or Zircon). Subsequent presowing preparation is conventionally divided into 3 scenarios depending on the species.

1. Acer BUERGERIANUM, Acer GINNALA, Acer ELEGANTULUM, Acer MACROPHYLLUM, Acer PALMATUM, Acer PLATANOIDES, Acer SACCHARUM, Acer TATARICUM, Acer TRUNCATUM (and most species not present in the list)

require cold stratification for successful germination. The seeds are placed into a small resealable plastic bag, inside of which lightly moistened peat moss or vermiculite is added beforehand, from which no water should squeeze out when pressed. Air is removed by running a palm from the bottom to the seal, the bag is tightly closed and placed on the lower shelf of the refrigerator. Stratification is carried out for 2-4 months at a temperature of 3-5 °C (37-41 °F). Once every 1-2 weeks, the contents are inspected. If condensation appears, excess moisture is removed by gentle pressing, after which the bag is flipped. In case the substrate dries out, 1-2 drops of water are added. Once germination begins, seeds are removed from the refrigerator and planted into prepared soil.

2. Acer CAMPESTRE, Acer GLABRUM, Acer GRISEUM, Acer JAPONICUM, Acer PSEUDOSIEBOLDIANUM, Acer SHIRASAWANUM (and challenging rare/montane/Asian species)

due to germination difficulty, require an additional warm stratification stage. After scarification and soaking, the seeds are kept in a warm room at a temperature of 20-30 °C (68-86 °F) for 2-4 months. Next, the seeds are placed in a plastic bag and undergo cold stratification (as described in point 1), sometimes with a repeated cycle. Low germination should come as no surprise, realistic expectations are only about 20-30%. Once germination begins, seeds are planted into prepared soil.

3. Acer RUBRUM, Acer SACCHARINUM (and hybrids such as Acer × FREEMANII)

do not require stratification and are sown immediately following scarification and soaking.

Following any of the preparatory stages, seeds are sown into a lightweight, breathable substrate to a depth equal to seed size or buried 0.5-1 cm (0.2-0.4 in) deep, moistened with a spray bottle, placed in a propagator or covered with film, and germinated in light but not in direct sun at a temperature of 18-22 °C (64-72 °F). Seedlings require ventilation. Overwatering and desiccation of the sowings must be avoided.

Seedlings appear in 2-4 weeks, the maximum germination period may exceed 6-8 weeks, and a portion of seeds may germinate only in the 2nd-3rd year. After the first true leaves expand, pricking out is carried out into individual small pots. Cultivar forms are also propagated by grafting onto sturdy rootstocks to preserve ornamental coloration.

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Maple prefers sunny or partially shaded locations, where ornamental foliage coloration displays most vividly. The plant tolerates urban conditions well, being resistant to wind and smoke pollution. In the initial years following planting, regular soil moisture and mulching of the tree well are recommended to preserve moisture. Best results are achieved on fertile, loose, and moderately moist soils with good drainage.

Watering is carried out regularly during hot and dry spells, approximately 10-15 L (2.6-4.0 gal) per plant, with a double rate after planting. In normal years, watering is performed once a month, and during hot periods - once a week. Maple can tolerate short-term soil dryness, but optimal growth is achieved with steady moisture. The plant possesses a shallow root system, so cultivation is performed carefully and shallowly. After planting, the base zone is mulched with a layer 3-5 cm (1.2-2.0 in) thick.

In early spring, sanitary and formative pruning is conducted: damaged, crowding, and diseased shoots are removed. In variegated forms and brightly colored cultivars, green reversion shoots may appear, which are pruned to the base so they do not suppress the ornamental part of the crown. Fertilizers are applied annually: in spring - balanced fertilizers with moderate nitrogen content, and in summer - phosphorus-potassium blends that promote shoot hardening.

Most maples are cold-hardy and require no shelter. Young plants during severe winters are recommended to be protected by mounding leaf litter or spruce boughs around the root collar zone. If annual shoots suffer frost damage, spring pruning is carried out - the crown recovers successfully through new growth flushes. With age, the cold hardiness of the plant increases.