Generally speaking, there are 2 types of deer repellents. Taste repellents and Scent repellents. Some repellents work by both means.
a) Taste repellents require that a deer sample your plant before determining that it is not particularly good to eat. Repetitive "samplings" by different deer on different nights throughout the winter can leave a plant slightly damaged, but generally speaking they work well.
b) Scent repellents leave an odor that discourages deer from approaching a specific plant or area. They work very well, but can quickly become ineffective, leaving your plantings completely unprotected.
To ensure success, a deer repellent should possess BOTH qualities, even if it means mixing two different repellents together. For winter protection, it's crucial that the repellent be mixed at it's most potent rate, as per the manufacturers instructions. It should also be promptly applied as often as the manufacturer suggests, or even slightly more often. Repetitive applications made throughout the winter will ensure your absolute success. The most vital time of all is late winter and early spring. This is the point at which deer are most desperate for forage. If you have diligently applied repellents throughout the winter, but stopped in mid or late February, you are going to be in for a very unpleasant surprise in mid to late March as the repellent loses it's effectiveness.
Consider purchasing a good quality tank sprayer to apply deer repellent with, and keeping it solely for this purpose. Below are some tips about tank sprayers:
a) If you have some spray left in the tank, make sure and store it in a frost-free area.
b) Do not store spray inside the tank for more than a week. Most repellents will start coagulating and causing problems with clogging the tank sprayer.
c) If you use Wilt-Pruf as a sticking agent mixed with the repellent, make sure to use it ALL in the same day. Wilt-Pruf quickly gums-up and can ruin your sprayer.
d) Thoroughly rinse your sprayer out with warm water several times after using a repellent, especially if it was mixed with Wilt-Pruf
Common Brands of Deer Repellents and their Attributes:
Bobbex: An organic foliar fertilizer that is marketed as an animal repellent. Made with several disgusting but effective additives derived from plant, animal and fish matter. Bobbex functions as both a taste and scent repellent. Active-Growing-Season applications should be made every 10 days on new growth. Dormant-Season applications MAY last as long as 2 months IF mixed at a strong dilution rate. Can be used on vegetables except those with edible leaves and stems. Odor is extremely offensive until thoroughly dry. Available in ready-to-use and concentrate form.
Deer Off: An organic repellent made from putrescent egg solids, hot pepper juice and garlic juice and is both a taste and scent repellent. Active-Growing-Season applications should be made every 10 days on new growth. Dormant-Season applications MAY last as long as 2 to 3 months under normal weather conditions and deer pressure. Available in ready-to-use form and concentrate. Odor is offensive until dry.
Deer Scram: An organic repellent made from animal matter in a dry-granular form. Functions as a scent repellent and is applied on the ground, in a band around the area that you want to protect. Manufacturer claims effectiveness for up to 2 months between applications.
Liquid Fence: An organic repellent made mostly from putrescent egg and garlic. Functions as both a taste and scent repellent. The manufacturer suggests that when used on a regular schedule, that it MAY last as long as 4 weeks between applications, year round on ornamentals. NOT for use on edibles.
Milorganite: An organic lawn and garden fertilizer available in granular form. Derived from dried, baked, granulated sewage sludge form the city of Milwaukee. While it is NOT marketed as a deer repellent, it does seem to be quite effective. It will not burn foliage, so it can actually be sprinkled ON the leaves of ornamental plants that you want to protect, ideally while they are lightly wet from a recent rain (Hosta's are the perfect example of this) While not as effective, it can also be applied on the ground in a band around the plants. It is very cost effective, but needs to be applied fairly often to ensure effectiveness.
Deer Out: An all natural repellent that has a pleasant peppermint fresh scent. It works by both smell and taste. Containing two all natural stickers, it can last longer than most repellents. Deer Out claims their product will not burn, stain, or discolor plant material. It is a very cost effective repellent.
SuperRepellent: A multi-mix blend of botanical oils. Provides for a wide spectrum of animal repellency while also repelling many insects as well. Since it does not contain any egg products, it is safe to use on edible crops. Just wash them off before eating.