Hello, I'm sorry to hear about your pups. You are likely describing hives which are a dog's way of responding to something they are allergic to.

Most of the plants that we react to such as poison oak or ivy or nettles dogs seem resistant to the effects of. However they can have facial swelling from insects found in brush which can bite or sting. And insect bites or stings are the most common cause of hives. If the yard is overgrown and has long weeds cutting plants short will help decrease the areas where insects can hide thus decreasing their exposure.

If this is related to inhaled allergies (pollens) then the only way to decrease their risk is to have them allergy tested and then remove the offending plants. That can be done via blood testing or with an intradermal skin test where small amounts of the allergen is injected under the skin to see whether they react or not.

If that isn't possible then I recommend giving Benedryl (diphenhydramine) at 1mg per pound orally every 8 hours for the next 72 hours when a reaction occurs or long term during the summer months to prevent the reaction from occuring. That's two 25mg tablet per 50 pounds of body weight 3 times daily. Antihistamines can make them sleepy but that effect usually decreases with repeated use and they are fairly safe to use long term as long as your dog doesn't have some types of heart disease or glaucoma.

If your pups vomit, have difficulty breathing or are very lethargic they should be seen by a veterinarian as that can signify dangerous worsening of an allergic reaction and that will require injections of steroids.

Giving a bath with cool water and an oatmeal shampoo and conditioner may be helpful too. The cool water constricts the capillaries and stops absorption of toxins and the water also washes away allergens. Oatmeal is very soothing for hives and should help quite them down a bit and relieve itching.

Let me know if you have any further questions.