Deer
Nothing but nothing will stop deer who are hungry enough from ravaging your ornamental garden. Deer will even sometimes eat highly toxic plants. Tasty plants like Hosta are deer magnets if you live in an area where deer are endemic. Short of building an 8-foot fence around your garden (deer can easily jump anything lower) there is no sure-fire way to prevent deer from roaming about your garden.
Having said that, there are fairly effective ways to deter deer from eating and possibly destroying your garden. First, you can utilize toxic and deer-resistant plants in your garden. Second, you will need to use deer deterrents to discourage browsing. (Deer will then probably go to someone else’s garden to ravage.)
General Strategy
We have found that a combination strategy of using nontoxic deterrent sprays, and mechanical deterrents can be effective in minimizing deer damage. Our rural area is overrun with deer (up to 80 per square mile) and deer frequently roam village streets and lawns. Before instituting control strategies, deer regularly destroyed our garden each summer.
Repellent Sprays
There are lots of opinions about deer deterrents, but scientific research done on the effectiveness of various deterrents suggest that only those repellents that have “putrescent egg solids” or similar artificial sulfur-based odorants as an ingredient, are statistically effective at reducing browsing. We have found that Deer-Off (now rebranded as Safer Critter Ridder Deer and Rabbit Repellent), a repellent containing putrescent egg solids plus capsaicin (the chemical compound responsible for the “heat” in chile peppers) is a highly effective deterrent. It works for several weeks, but must be reapplied after heavy rain. We spray it only on the most deer sensitive plants in our garden. To humans, the odor is not particularly detectable, but apparently it is highly repellent to deer and other plant-browsing pests. Animals that attempt to eat treated plants anyway get a mouthful of capsaicin, which serves as secondary deterrent, although this ingredient has not been widely studied in scientific trials. Any brand pest repellent spray with egg solids should be effective. We have found an alternative product, I Must Garden Deer Repellent, that also appears to be effective. This product contains cinnamon and clove oil, garlic extract, and white pepper, as well as egg solids. It has a more pleasant smell than most egg-based repellents, and we have used it in our garden frequently. Liquid Fence is another product that works. It contiains thyme oil as an additional odorant. Unfortunately, we find the odor from the combination of egg solids and thyme oil repellent to us! We don't use it anymore. Maybe you will find the smell more pleasant than we do. The only negative we have found with all of these repellents is that they can leave unsightly “spots” on your foliage, which is especially apparent for non-variegated or darker-colored plants. Spotted plants are nicer to look at than perennial stumps or half-eaten plants, however.
We have fortuitously discovered that consistent and repeated application of deterrents early in the garden season decreases browsing throughout the year. (Deer still eat Hosta flowers in our garden but rarely attack the foliage anymore.) It is possible there is a “training factor” for resident pests who learn to avoid treated plants. This can come in handy during prolonged periods of rain. It is during such periods, when repellents get washed away and we cannot re-treat, that we have suffered the most extensive garden damage from deer.
Our recommendation is to buy repellents in concentrate form and mix your own repellent solution for dispensing from a 1 gallon garden sprayer. Re-apply after every heavy rain, otherwise treatments should be effective for a few weeks to a month or so. To minimize usage, treat only those plants that deer will browse. You can use this site as a guide as to which plants are not usually bothered by deer.
Mechanical Repellents
We have found that a motion-activated water sprinkler can be an effective deterrent to deer. We place our in locations that are near the entry points for deer into our property. Based on our security camera images, we know that deer do not like the sprinklers! We only have one of these units, so it gets moved around to various spots in the garden to keep the deer guessing. The model we use, an Orbit Yard Enforcer, can be set to activate only after dark, so that you don't soak yourself during the daytime. However, we have been known to be unceremoniously soaked in the early evening when forgetting we have armed them. The sprinkler can be hidden among the garden foliage to keep it partially out of sight.