Following a survey conducted among various fig tree enthusiasts, who grow this plant in border-line or extremely cold conditions, I noticed with some surprise, the divergence away from planting in the fig tree’s original preferred and natural environment.
In fact, it would be normal to consider that young and vigorous fig plants may be damaged or completely killed by ground frost, when temperatures drop to between -2 and -4°C.
On the other hand, if it benefits from protection during the first years and succeeds in developing, the fig tree may easily resist temperatures of between -15° and -17°C, and even less for some varieties, when planted in very good locations (-18°C at least).
Structure and physiology of the fig tree
The fig tree has a mixed constitution, herbaceous and woody. This structure can be observed in Spring, and when new branches appear, they are gorged with lymph. Lymph is a milky liquid, rich in water, resin and accumulated substances (starch) that with the exception of water, make an excellent anti-freeze.
The new vegetation mainly uses these accumulated substances which are available within the wood. Therefore it is not surprising that new growth is so vigorous in spring; actually the plant uses the energy accumulated during the previous year, in the form of carbohydrate.
The fig tree is in part a succulent plant that lives in hot desert-like zones and is then programmed to store huge quantities of water in its trunk, branches and roots, during the vegetative growth. In fact, in its natural environment, rains are rare and droughts are frequent.
The accumulation of substances in reserve, inside its wood and roots (resin and carbohydrates) is due to the metabolism of the plant (by light, heat).
These conditions are fundamental for fruit ripening.
The natural environment of the fig tree
In its original habitat, the fig tree lives in soils that are very well drained, sunny, hot and arid.
The fig tree prefers to grow on rocks or hills, where the soil is free-draining, getting sun and heat from all sides, rather than in very rich, cold soils.
Often, the neighboring rocks and soils are bare and reflect the heat; the grass around the plant is non-existent and the soil is therefore dry and burned by the sun.
At the end of the summer, when the fruits are ripe, they have very little water at their disposal and hence are very sweet.
The wood is very dehydrated as the long, hot and bright summer concentrates the anti-freeze substances (resin and starch), making it lose the herbaceous consistency and allowing it to take a “dry” appearance.
In this state, the plant resists cold to temperatures 10° to 12°C lower than for the herbaceous structure.
The Autumn rains occur when the vegetative cycle is completed and have almost no effect on hydration.
In its normal environment, fertilization is poor and often achieved at a low level, with decomposing branches and sprigs. The reduced soil fertility does not encourage new growth of herbaceous parts.
To illustrate this case, in England, it is not surprising that mature fig trees, reputedly hardy, succumb to frost at -5°C and below. In these regions where summers are cool with frequent rains, planting fig trees in half shade or full shade can be a disaster, as new growth doesn’t harden correctly and the branches remain in a herbaceous state. In this case, Winter protective sheets will not be effective because the herbaceous part will be lost and severe trimming will be required.
What action can be taken?
It is obvious that for a gardener, it is impossible to prevent rain or modify the climate.
However, it is possible to avoid planting a fig tree where water stagnates. If the plant stays in a humid environment, it will continue to gorge itself with water. It is then mandatory to select arid or at least very well drained locations.
Consequently, it is evident that hills or sloping land are the ideal sites. Basically, a deep draining system is fundamental. It is also possible to create a big mound made of pebbles, compost and slightly enriched garden soil. The fig tree should be planted on the south and sunny side of the mound.
Around the plant, the soil must be bare, weeded and well hoed. Nevertheless, there can be grass but it must be mown as otherwise it retains humidity. Below the grass, the ground always stays humid; this may only be visible with morning dews. The consequence is that during an important part of the day, humidity evaporates from the ground and reduces heat in a significant way. As a result, the metabolism of the plant is slowed down and less sugar is accumulated in the fruits as well as less resin and starch in the wood, which are necessary for resisting against frost in winter.
Do not water around the fig tree as the roots are often much longer than the branches!
When Autumn arrives, if the plant is vigorous and still growing with herbaceous branches, this is a bad sign, because it means that the fig tree did not receive enough heat to harden its wood. In fact, the fig tree is wasting nutritional reserves to produce nothing useful as the herbaceous branches will be destroyed by the first frosts. As a consequence, the subsequent year fruiting (first crop or breba) is compromised. Furthermore, with the diminishing reserves, the anti-freeze substances are diluted with water in the herbaceous branches, which then definitely can’t resist the winter frosts.
The soil may be lightly fertilized, but never after the month of June. The young plants are prone to be more herbaceous and are therefore more delicate; on the contrary a good hardening of the wood enhances greatly the resistance to frost.
In cold areas, it is advisable to protect young fig trees during their first winter. It is recommended to build a “teepee” covered with Winter protective sheeting around the fig tree, three-quarters filled with dead leaves which slowly decompose (plane-tree leaves are ideal).
Only uncover the fig tree after the last frosts, but no later, as even a slight frost of -2°C can destroy the tender green buds with all their fruiting potential. Ensure you uncover the fig tree promptly to avoid early sprouting which would be enhanced by excessive covering. After two or three years, this protection will no longer be necessary. Even with these measures, a fig tree planted in a wrong location will not succeed in a cold area. The best location, sunny south or south-west facing should be provided.
When planting a fig tree against a wall, keep in mind that it develops powerful roots and that eventually, it is possible that they may penetrate and damage drain pipes. Furthermore, if your house is very old, the roots will attempt to infiltrate any gaps in the mortar.
If you have the opportunity to travel to the south of Europe, observe the fig tree in its natural environment, growing wild on dry stone walls or rocks.
Often you will find fig trees planted near stone walls or houses, where they always receive a lot of sun and reflected heat, during many hours of the day.
In conclusion, a micro-climate, natural or artificial may also make a difference. (click here to see the original Italian version of this article)