Traditional folklore says that if the hedge apples are arranged around the foundation of a house or along the inside basement wall that pests such as mice and spiders will be repelled and won’t try to enter the home.
Hedge Apple Juice
A study conducted by the University of Nebraska showed that if the juices of a hedge apple can be extracted and concentrated then it is a fairly effective repellent. However, the process of collecting the juices and getting enough to create a concentrate is fairly labor intensive. This is due to the fact that the fruit is very woody with the inside of the fruit being about as tough and rigid as the outside.
Whole Hedge Apple
The traditional methods of using hedge apples require that the whole fruit be allowed to turn green and then be placed along the foundation of where mice and unwanted pests may find access to the building. However, neither a study completed by the University of Nebraska nor a similar study conducted at the University of Iowa produced any results that suggested this method was effective at repelling mice or any other kind of pest.
Effectiveness
According to the Department of Horticulture at Iowa State University, hedge apples have been promoted as a pest solution for years. However, the department found that the claims are not backed by scientific research. So while hege apples are still commonly sold at farmer's market as a form of pest repellent they may not be worth the price.