I just found some of these home remedies for common garden/plant problems. I haven't tried any yet so don't know the effectiveness of any of them. Since all are made with items typically on hand in the household you don't have much to lose to give them a try. Let me know if any work for you.
Slugs: This one seems to be well known and does have validity. Beer traps for slugs. Using a mason jar or other jar of similar size. Dig a hole and place jar in the ground so that the top of jar is level with the ground. Fill jar with beer leaving 1 inch head space. The slugs will belly up to the bar and dive in.
Tomatoe Blossom end rot - put crushed eggshells around plants
Black spot on roses - 1 part milk to 2 parts water. Spray roses once per week. The lactifern in the milk attacks the blackspot fungi
Deer - I don't know about this one...would take a whole hen house to rid the deer around here. But I guess if they are just bothering certain plants it might be worth a try.
Blend 4 eggs to 1 quart of water, put in sprayer and spray plants
House plant insects - soap water, I have used this successfully on aphids
Powdery mildew - Soap water & baking soda.
Spider mites & mealy bugs - blend habenero peppers & water, put in sprayer and spray once per week. DANGER..take care to wear gloves when working with hot peppers.