Foxtails on a cannabis plant refer to an irregular growth where the many small calyxs that typically grow stacked and tight in a long cone structure to create buds, grow outward at an odd shape instead with many long, gangly shoots coming off of what should be tight buds. Foxtailing is usually a disappointment unless the genetics are designed to grow that way, although genetically predisposed foxtails have a very different appearance than foxtails caused by stress.
Foxtails caused by genetics appear as calyxs that ‘shoot’ off the bud but remain close to the main bud, which is a part of the foxtailing process, and all foxtails are uniform, not long, and odd-shaped. These foxtail buds can be just as potent, although many growers still prefer dense, packed buds without the foxtailing effect. Foxtails occur more frequently in Sativa strains with feminized or autoflowers.
The biggest cause of foxtailing is stress from excessive light and heat. Adjust the lighting as your plants grow, as lights that are too close or too intense to your buds could cause foxtailing. If you notice upper leaves changing color to yellow or white, this is an early sign of light stress when the leaves remain relatively strong as opposed to wilting, yellowing leaves, which is a sign of nitrogen deficiency.
Other causes could be harmful microbes, uncontrolled pH, and stressful growing conditions. Constantly check your heat and light, pH, and microbial balance, and make sure your plants have plenty of space to avoid root stress to help prevent foxtailing.