We recommend that you mow your lawn 1-2 days prior to applying the Mosquito Barrier for mosquito control. It is recommended that you wait at least 24 hours after applying the product to mow.
There is nothing that can be added to the Mosquito Barrier to reduce the smell as that garlic smell is what repels insects from the area in the first place. The smell of the garlic juice will become unnoticeable to humans within a few minutes and will only be strong during and right after application.
Mosquito Barrier is meant to be applied to lawns, ornamentals, and trees, not hard surfaces like wood. It should be applied to the underside of leaves of bushes, shrubs, ornamentals, and low lying tree branches as that is where the adults lay during the day and it will help to repel them from areas it is applied to which can help around the porch if close enough. Otherwise something like the Dynatrap Indoor / Outdoor Insect Trap with Optional Wall Mount (DT1100) could be used up on the deck.
There is nothing that can be added to the Mosquito Barrier to reduce the smell as that garlic smell is what repels insects from the area in the first place. The smell of the garlic oil will become unnoticeable to humans within a few minutes and will only be strong during and right after application. It could take 24 hrs or so to kill unless sprayed directly and it offers a 4 week residual.
For non chemical products there are not a lot of options to increase the residual. You could potentially mix the Mosquito Barrier (that while states it has a residual is more of a temporary repellent and contact kill) with an all natural insecticide like Essentria IC3. Essentria will typically hold up to the outdoor elements around 30 days depending on the weather as all natural oil based products tend to break down in sunlight faster than chemical residual products.
For chemical products you could go with something like Bifen or Suspend Polyzone for a longer residual. But here's the issue with using any residual killing insecticide whether natural/non chemical or chemical based with Mosquito Barrier.
While you could tank mix the two, the Mosquito Barrier is going to work against the effectiveness of the residual product for probably at least the first week or two. You are spraying Bifen/Suspend Poly/Essentria on surfaces moquitoes would land on and harbor in so that when they touch the treated surface they pick it up on their bodies and die from it. If you are spraying Mosquito Barrier you are using it to repel the mosquitoes away from areas you dont want them or are trying to keep them from harboring. So essentially by mixing the two together, you are repelling the mosquitoes away from the Bifen/Suspend Poly/Essentria to not die from it. Outside of an initial contact kill the mosquito barrier isn't going to provide killing action for you long term, only repellency. The residual products are actually the better products to use on a consistent basis in main target areas on the property where mosquitoes would be found, and use the Mosquito Barrier around patios and hang out areas to keep them at bay until they have died from landing on the residual product treated surfaces.
That being said, if you choose to go with suedo chemical products, using an IGR (Nyguard or Tekko) to help stop the reproductive cycle of the mosquitoes or a larvacide (Altosid) in standing water areas on or near the property where the main problem could be imminating from should drastically increase the results you see long term as well.
The Mosquito Barrier has a three year shelf life from the date of purchase (if stored away from extreme temperatures in a cool, dry place).