Grapevines are one of the garden plants that require regular and often extensive pruning in winter or spring. If you have tried pruning your grapevines, you most likely have noticed water dripping from the freshly cut branches. You may also be curious why this happens.
Grapevines drip water once cut because their stems are filled with fluid. The water dripping from the cut stems is, in reality, grapevine sap, which contains plenty of nutrients for the plant. You will find more sap when you prune your vines during the growing season in spring.
This article will discuss the science behind why grapevines drip water –often referred to as bleeding sap or grapevine bleeding– and its impact on the plant. I will also share how to avoid it and several possible uses for grapevine sap.
- Sap Release and Pruning Time: Grapevines release nutrient-rich sap when pruned due to their advanced vascular system. Optimal pruning time is late winter or early spring to minimize sap loss.
- Vascular and Root System Dynamics: The grapevine’s xylem and phloem facilitate water and nutrient movement, while the roots store and draw nutrients, influencing sap flow.
- Pruning Techniques: Cut stems diagonally at 45-60° to reduce microbial risks and promote healthy growth.
- Potential Uses of Sap: Grapevine sap can be used as an antioxidant and in cosmetics, but caution is needed due to potential contamination.
- Safety Considerations: Processed sap is safer for use in health and beauty products, while unprocessed sap may contain harmful microorganisms.
The Science Behind Grapevine Bleeding
Plants absorb water through their roots and deliver it to the shoots above ground through a vascular system consisting of the xylem and the phloem. Grapevines have an extensive root system and an efficient vascular system.
The xylem typically carries water and nutrients from the roots upwards. The upward movement of the water is due to the pressure triggered by the transpiration rate that requires the vine’s water supply to be replenished. On the other hand, the phloem distributes sugars and amino acids upwards and downwards.
A grapevine’s phloem layers lie next to the bark, while the xylem is closer to the pith. When you cut through the vine’s stem, the water or sap that drips from it consists of the water and nutrients actively moving through the plant’s vascular system.
In winter, as the grapevine enters dormancy, the excess sugars and amino acids build up into starch and proteins stored in the roots’ vascular system, along with nitrogen and other nutrients. As the soil temperatures warm enough for chemical reactions to occur, the starch and proteins break down once again.
The high concentration of mineral salts, sugars, and amino acids in the roots stimulates them to draw in water from the ground. Grapevines typically have an extensive root system that allows them to find and absorb as much moisture as necessary during the growing season.
The function of the roots mainly depends on the amount of moisture and nutrients in the plant. If there is a shortage, the grapevine will focus much of its energy on root growth by closing some stomata and slowing down shoot growth.
The increased root growth focuses on finding access to more moisture and nutrients in the soil. Once the roots adequately supply the plant’s needs, the shoots will resume normal growth.
Grape vines tend to grow quickly despite heavy pruning due to the roots’ impressive ability to actively seek out water and minerals in the soil.
Ideally, you must prune grapevines in late winter or early spring because these plants produce fruits on new growth. Since the vines require heavy pruning, you will likely notice the sap oozing from the stems, especially when the plants wake up from their winter dormancy.
During this time, the xylem pulls up more moisture and minerals from the ground to jumpstart the plant’s growth. Meanwhile, the phloem transports essential sugars and amino acids to aid the plant’s development.
The sap also contains several other chemicals that aid the grape vine’s overall health. Some of these nutrients are also present in the fruits. In addition, the sap has antifungal properties to fight against harmful microbes, such as Botrytis cinerea.
When pruning grapevines for new growth, cut the ends diagonally at an angle between 45-60° to prevent moisture buildup that can invite unwanted microbial infections. The sap is not potent enough to ward off all harmful microbes.
Best Pruning Period to Reduce Sap Loss
Although the grapevines’ sap does not pose any harm to the plants or to humans, some gardeners may find it unpleasant. It can be challenging to prevent the vines from dripping water when cut, but you can reduce the amount of sap coming out by timing your pruning properly.
Grape vines require pruning before the growing season in spring. Pruning them too late can result in wasted nutrients and moisture. A large amount of sap coming out of your grapevine stems indicates that you pruned your plant too late.
Cutting back the branches and stems in winter will result in less dripping than when you do it in early spring. However, during long and harsh winters, your grapevines might suffer winter injury if you prune them too early, making proper timing essential.
Depending on your area, the best time to prune grapevines is late winter or early spring, ideally when temperatures rise to 41 °F (5 °C) and stay well around that level for one to two weeks. It eliminates the threat of frost damaging your plants while still below the optimum temperature to jumpstart the chemical reactions that activate plant growth.
If you cannot seem to find the perfect timing for pruning your grapevines, you can find alternative uses for the sap.
Possible Uses for Grapevine Sap
Vitis vinifera or grapes are renowned for their delicious, juicy fruits that are processed to make wine. Whether raw or processed, the plant’s fruits pack a lot of benefits to human health. Traditionally, the sap from the vines was also used as an alternative medicine for specific health conditions.
Let’s check out the alternative uses of grapevine sap:
Grapes and wine are popular not only because of their flavor but also due to their antioxidant properties. The grapevine’s sap also contains antioxidants, making it a suitable and healthy drink–if you don’t mind its bitter taste.
However, more studies are necessary to prove the effectiveness of the grape vine’s sap on the human body. Although plenty of research has been done to verify the health benefits of grape fruit and wine, grape sap is not yet widely harvested for such purposes.
Moreover, different grapevine varieties contain varying levels of nutrients. The environmental conditions and the various types and levels of minerals in the soil can also affect the plant’s overall nutritional content.
Traditional use of grapevine sap includes treatment for acne and other skin conditions. Although it requires more scientific evidence, the sap was also used to relieve itchy skin rashes. Similar to aloe vera, grapevine sap is also believed to possess anti-inflammatory and antimicrobial properties.
Because of its historical applications, the sap is slowly gaining popularity among modern cosmetics manufacturers specializing in biocosmetics or beauty products derived from natural and organic sources. Some cosmetics companies use grapevine’s sap, fruits, and leaves as a skin conditioning agent.
Although some cosmetics companies market grapevine sap as an effective remedy for common skin problems, it is important to understand that these companies have a research team and equipment to make the sap as safe for human use as possible.
Traditionally, there may be people who used unprocessed grapevine sap and claimed it to be effective. Still, there might also be some who saw the opposite results.
Most of the negative results come from the harmful microorganisms that may be present on the surface of the stem. They can contaminate the sap upon contact when you try to catch it as it drips.
Although the sap has antifungal properties, it may not be enough to kill off other fungi, viruses, and bacteria. These harmful microbes might be responsible for the adverse reactions when you use the raw sap.
Grape vines drip water or bleed sap when pruned in spring due to the activities of their vascular system. The roots deliver water upward to the parts of the plant above the ground. In contrast, the phloem transports essential nutrients to support root growth.
You can reduce the amount of sap coming out of your grape vines by pruning your plants late in winter before they start actively growing.
You can also repurpose the sap as an antioxidant drink or skin conditioner, but you must use it cautiously as it may pose some risks when unprocessed.