Delphiniums, often recognized as larkspur, are popular perennial flowers known for their dramatic, tall spires and vivid blue, purple, and white blossoms. These stately plants create a striking vertical element in garden beds and are a staple in cottage garden designs. A frequent concern for gardeners is protecting these ornamental plants from browsing deer, which can quickly devastate a flower bed.
The Resistance Rating: Why Deer Avoid Delphiniums
Delphiniums are generally classified as highly deer resistant, meaning they are seldom or rarely damaged by deer browsing. This high level of resistance is not due to a physical barrier but rather a sophisticated chemical defense system within the plant’s structure. The entire plant, including the leaves, stems, and seeds, contains a concentration of toxic compounds known as diterpenoid alkaloids.
The primary defense mechanism is the presence of potent neurotoxins like methyllycaconitine (MLA) and delphinine. These alkaloids are extremely bitter and can be poisonous to mammals, including deer and livestock, if ingested in sufficient quantities. The compounds act on the nervous system, potentially causing symptoms ranging from digestive upset to cardiotoxic effects and respiratory failure. Deer instinctively avoid the plant, as their foraging behavior guides them toward safer food sources.
When Resistance Fails: Situational Factors
The term “deer resistant” does not mean “deer proof,” and browsing damage can still occur under specific environmental pressures. When natural browse is scarce, a hungry deer will often override its natural aversion to bitter or toxic plants. Extreme weather events, such as severe drought or deep, persistent snow, can eliminate preferred food sources, forcing deer to sample plants they would normally ignore. Localized high deer population density also increases the likelihood of browsing, as competition for food intensifies.
Delphiniums are most vulnerable in the early spring when tender new growth emerges from the soil. The alkaloid concentration in this young tissue may be lower than in mature foliage, making the plant temporarily more appealing. If a deer samples the new shoots and finds them tolerable, browsing may continue before the plant’s full chemical defense system is mobilized.
Protecting Your Plants: Effective Deterrent Strategies
Gardeners facing persistent browsing can employ a multi-layered approach using both physical and chemical interventions to protect their delphiniums. The most effective long-term solution is a physical barrier, such as a sturdy fence at least seven or eight feet tall, which is necessary to prevent deer from jumping over. For localized protection of individual plants, temporary netting can be draped over young delphiniums in the spring to shield the vulnerable new shoots.
Chemical deterrents work by appealing to a deer’s strong sense of smell or taste, making the foliage unpleasant. Commercial repellent sprays, which often contain ingredients like putrefied egg solids, garlic, or capsaicin, should be applied directly to the plant foliage. A homemade solution using a mixture of three eggs thoroughly blended with a gallon of water is a popular and cost-effective alternative. Repellents must be reapplied every two weeks and immediately after heavy rainfall to maintain effectiveness.
Another cultural practice involves companion planting, which uses highly aromatic plants to mask the scent of more desirable species. Planting strongly scented herbs, such as lavender, rosemary, or Russian sage, around the perimeter of a delphinium bed can help create a sensory barrier. Rotating different types of deterrents is also advisable to prevent deer from becoming accustomed to one specific scent or taste.