Slash pine is named for the slashes of swampy ground in which it grows. This fast-growing conifer is used for reforestation projects, turpentine, and other crude rosins. It is also known as Swamp Pine and Southern Florida Pine.
I. Appearance and Characteristics
Pinus elliottii, commonly known as slash pine, is a conifer tree native to the Southeastern United States. Slash pine is named after the “slashes” – swampy ground overgrown with trees and bushes – that constitute its habitat. Other common names include swamp pine, yellow slash pine, and southern Florida pine.
This tree is fast-growing, but not very long-lived by pine standards (to 200 years). It reaches heights of 18–30 m (59–98 ft) with a trunk diameter of 0.6–0.8 m (2.0–2.6 ft). The leaves are needle-like, very slender, in clusters of two or three, and 18–24 cm (7.1–9.4 in) long. The cones are glossy red-brown, 5–15 cm (2.0–5.9 in) in length, with a short (2–3 mm or 0.079–0.118 in), thick prickle on each scale. It is known for its conical shape and unusually high strength, especially for a pine. Its wood has an average crush strength of 8,140 lb/in2 (56.1 MPa), which exceeds many hardwoods such as white ash (7,410 lb/in2) and black maple (6,680 lb/in2). It is not as strong as black ironwood (9,940 lb/in2), but because its average density is less than half that of ironwood, slash pine has a far greater strength-to-weight ratio.
It may be distinguished from the related loblolly pine (P. taeda) by the somewhat longer, glossier needles and larger red-brown cones, and from longleaf pine (P. palustris) by the shorter, more slender needles and smaller cones with less broad scales.
Two varieties of P. elliotii are described, but recent genetic studies have indicated that the varieties may not be more closely related to each other than they are to other pines in the Southeast. If this is the case, reclassifying these varieties as separate species would be warranted. P. elliottii can hybridize with P. taeda, sand pine (Pinus clausa), and P. palustris.
The two commonly accepted varieties are the following:
P. e. var. elliottii (typical slash pine) ranges from South Carolina to Louisiana, and south to central Florida. Its leaves occur in bundles, fascicles of twos and threes, mostly threes, and the cones are larger, 7–15 cm (2.8–5.9 in).
P. e. var. densa (South Florida slash pine, Dade County pine) is found in the pine rocklands of southern Florida and the Florida Keys, including the Everglades. Leaves are nearly all in bundles of two, with longer needles. The cones are smaller, 5–12 cm (2.0–4.7 in), the wood is denser, and the tree has a thicker taproot. Unlike the typical variety of slash pine, seedlings of P. e. var. densa has a “grass stage” similar to longleaf pine. P. e. var. densa is not frost tolerant, which limits its range to South Florida.
II. How to Grow and Care
Sunlight
The slash pine can grow in both full sun and partial shade. When placed in a well-ventilated location with sufficient sunlight, the needles will be green and strong. In a hot location with insufficient sunlight, the needles will be weak and will easily turn yellow. Ideally, the plant needs around 5-6 hours of sunlight a day, with good ventilation.
Watering
For newly planted seedlings or new plants, water once every morning and evening during hot spells in the summer. Do not water midday, as this can cause root burn or strangle. Water plants according to your individual climate and rainfall in other seasons. For mature plants, only water when they are dry, keeping in mind that these plants are drought resistant. For indoor potted plants, spray water on the surfaces of the leaves once every morning and evening when it is dry. Be careful not to provide excess water – this hinders air circulation in a pot, leading to the rotting of roots and the withering of branches and leaves.
Soil
Slash pine can grow in a variety of different soil types, including bare mineral soil, sandy soil, volcanic ash, calcareous soil, limestone soil, and everything from dusty soil to red soil. Since it is resistant to drought, it will even grow in barren landscapes. However, it grows best in loose, fertile, well-drained, and slightly acidic soil. In the case of too much alkalinity, needles of potted plants will turn yellow and fall, so it is best to use natural mountain soil in pots and containers.
Fertilizing
The slash pine likes fertilizer and should be fertilized frequently, with just a small amount each time, during its growth period. It should be fertilized once a month in late spring, early summer, and fall. A fermented organic fertilizer is most effective for promoting growth.
Generally, do not apply a nitrogen fertilizer, such as urea or human urine, because pine needles already absorb nitrogen from the air, and pine roots are sensitive to nitrogen. You would be best off with a liquid fertilizer, applying this when the soil is dry in the afternoon. Water the plant again after fertilizer application, which will help with root absorption.
Do not use fertilizers that haven’t been fermented, or those with a higher concentration; the former will burn the roots and the latter will lead to the spindling of needles and more root damage, and could even cause the back-flow of sap, leading to water loss and the withering of the plant. No fertilizer should be applied in midsummer, during severe winters, or in the rainy season in the spring.
Generally, plants in gardens should be fertilized twice during the growth periods in spring and fall. Apply an organic fertilizer once before germination in the spring and apply slightly more fertilizer in the fall to promote robust growth. Stop fertilizing after midsummer so as to prevent spindling.
Planting Instructions
Slash pine is best planted in early spring. Ideally, use healthy and vigorous seedlings with soils balls, as this can greatly improve the survival rate. In the case of many lateral roots, the deep main root can be cut. Otherwise, the root system should be protected to avoid damage.
plant in a high, dry, well-drained, and well-ventilated place, with loose soil. In low-lying places with accumulated water, or places with sticky soil, try building a platform or changing the soil before planting. The planting pit should be treated with a basal fertilizer before planting. Newly planted large seedlings should be supported to prevent them being blown down by the wind. Before planting, excess branches should be pruned off. Protect the plant’s shape from damage as much as possible, as this will help to restore growth at a later stage.
Ideally, plant indoor potted plants in the spring, and repot every two or three years in the late fall or early spring. Repotting too frequently will lead to the death of the plant. If the plant is growing weakly, find out the cause of this and change the flowerpot soil, or replant in a larger pot.
Cut back on water before repotting, so as to keep the soil slightly dry. Remove the soil ball from the pot, keeping it whole, and then prune away any old roots from the bottom and sides. Remove some of the old soil from the middle of the soil ball, replace with new soil, apply a small amount of basal fertilizer, and then cover the plant with new soil. Ensure a suitable pot size – a deep pot will easily accumulate water, leading to root rot.
Pruning
For an indoor potted plant, any dead, diseased or damaged branches should be removed. You can then adjust the tree’s shape by pruning branches, pinching buds, and trimming leaves, giving you a better ornamental effect. Prune the plant before all of its needles fall off, so as to obtain a compact shape, richer lateral and side branches, and a better form overall. Pruning should be done during the dormancy period, so as to prevent excess loss of sap and damage to the plant’s vigor.
For a plant in a garden, dense lateral branches should be pruned so as to improve the survival rate. Remove excess lateral branches during the vigorous growth period based on needs, focusing on encouraging the trunk to grow tall and straight. Cut off any diseased or dead branches right away, so as to prevent the spread of pathogens.
Propagation
Slash pine is mainly propagated by seeds or branch cuttage. For family planting or potting, cultivated seedlings or pruned potted plants can be purchased from the market. Pay attention to pests, diseases, and appearance when selecting seedlings.
Pests and Diseases
- Fusiform rust
Starting in the late 1950s, the emergence of fusiform rust on Southeastern pine trees including slash pine, loblolly pine, and longleaf pine led to massive tree mortality within the pine industry. This obligate parasitic pathogen is notorious for infecting young trees in newly planted areas within the first few years of growing. The pine industry was still rather new at the time of this initial outbreak, so many newly planted forests had large-scale mortality because the trees were not yet old enough to be resilient to the disease or harvested.
Florida’s pine industry in particular was booming with an increase in plantation acreage from 291,000 acres (118,000 ha) in 1952 to upwards of 5.59 million acres (2,260,000 ha) in 1990. Because of the complicated life cycle of Cronaritum quercuum f. sp. fusiforme, the fungal causal agent of fusiform rust, the management strategies of pruning diseased stems, reducing fertilization, and discarding infected seed were not sufficient to prevent million-dollar annual losses.
There are many ways to go about reducing high-hazard areas for fusiform rust, but it starts with understanding why fusiform rust occurs more often during certain instances than others. Even though we have seen newer genetic work from seedling nurseries that has helped loblolly and slash pine become more resilient to fusiform rust, it is not always the case that landowners want to or can afford to buy the genetically modified seedlings so there are a couple of ways to help reduce the possibility of fusiform rust infected trees. The first initial step to take to reduce fusiform rust infection is to reduce the amount of site preparation used to establish the stand.
These site preps, while desired, cause increased rapid growth of pines. When this happens the outer layer of bark is thin enough for fusiform rust to infect and often it will be the main stem. When loblolly pine reach around the age of eight years old you can use more fertilization and forest prescriptions because at this time fusiform rust is not as likely to infect the main stem. Due to oaks being the alternate host for fusiform rust, where it lives out three of its spore lifecycles, it is a good idea to remove any hardwoods that are adjacent to your loblolly stand.
This can be difficult considering that oaks also share an importance in the economic and environmental aspect of the Southeast. Doing this will allow the pathogen to hit a dead end. In an older loblolly plantation, it is safe to keep those trees in rotation if the disease is not along the stem of the tree.
- Pitch canker
Pitch canker, a monocyclic disease caused by the fungus Fusarium circinatum (previously named Fusarium moniliforme var. subglutinans), was first described in 1946 by Hepting and Roth. When it was first described, disease levels were low until the 1970s, when a massive epidemic of pitch canker caused mass tree mortality in Florida slash pine. Some hypotheses suggest that the pathogen may have originated in Mexico and was then introduced in Florida and later transmitted to California on diseased seed.
The pathogen has been reported in Mexico; however, high fungal diversity and low tree mortality from the disease suggests that this pathogen may have co-evolved in Mexico before being introduced to other parts of the world. Many reports describe the pathogen as endemic to Florida, likely because the disease was introduced a long time therefore the population has become more diverse.
By 1974, over half of the slash pine population in Florida was infected with Fusarium circinatum disease. In areas where the pathogen is newly introduced, the fungal population is mostly clonal, because fewer mating types are present within the population, so sexual reproduction may be lower. Pitch canker infects nearly all pine species, including longleaf pine, shortleaf pine, and eastern white pine.
This disease continues to be a problem in nurseries, and has been reported in other countries. A major problem in Florida is that artificial replanting of pines may be contributing to high disease incidences. The disease can be passed through seed and spores, but requires open wounds to infect the tree from insect damage, mechanical damage, hail/weather damage, etc.
The predominant symptoms include needle chlorosis and reddening of shoots (called “flagging”) that later die. Cankers or lesions that form on the trunks can turn the bark yellow or dark brown and cause resin to exude. Stems may die and get crystalized in resin-soaked lesions. Resin is generally produced in plants to protect against pathogens. Sometimes, the tissue above the canker dies, causing girdling of the stem. The severity of the disease depends on weather conditions and may require moisture and insect wounds or hail to infect the trees.
Some insects such as bark beetles, spittle bugs, weevils, pine tip moths, and needle midges may vector the disease into the tree. F. circinatum was used to inoculate P. e. var. densa trees to try to increase resin production for extraction, but this approach was ineffective.
III. Uses and Benefits
The wood can be used to collect rosin; bark, needles, roots and so on can be comprehensively made into various chemical products; seeds can be extracted for oil.
