because of the cost of converting the whole garden at once, we just slowly converted to a drip/soaker style of irrigation. Our problem with overhead watering was that our garden doesn't get enough direct sunlight, and the water promoted disease on some types of plants. Once we got our garden converted fully to ground level/root irrigation, our disease problems have basically gone away. You have two different kinds, the plastic 6/8 mil hose and a rubber hose. The plastic is much cheaper even if you factor in buying all the fittings. However, the plastic only lasts a few years, and even less if you actually bury it. Since we knew we were going to have a garden for years to come, we decided the best bang for our buck was to slowly acquire the rubber type soaker/drip hose. Usually the best deal comes at Wal-mart, where you can get 50' for just under ten bucks. It comes with a 7 year manufacturer warranty. If you lay the hose one way, it sprays water upwards onto the bottom of the plants and if you turn it around the other, it soaks the ground, getting water quickly to the roots and using the least amount of water possible. My garden is big and we needed several hundred feet to cover most all of the garden. We just bought a hundred feet or so several times a year and after 3 or 4 years we had the footage to irrigate the whole garden using this method. In my opinion it is by far the best way to water. You don't lose much water to evaporation, you cut down on the start and spread of disease, and it helps control weeds since you are minimizing the open space you are watering.
We put our plants in 100' rows so that two of the hoses connected together would do a whole row. We usually have 6 rows, and this isn't counting our corn and bean varieties, which are still watered overhead. Since we water from one regular spiggot, we used to irrigate one section per day for a whole hour to get the amount of water we needed. And we alternated between 3 sprinklers. We also ran our sprinklers on the corn and beans for 30 min every day. With the soaker hose system we hook up 2 of the 100' lines at a time, and they only have to be on for 15 to 20 min and that still gives us more than what an hour of overhead gave us before. So in just a little over an hour, we are watering our whole garden. This would of taken an hour per day over the course of 2 or 3 days with the old method. We could of watered every section for an hour every day, but the spiggot we use is run with the same pump that runs the house, so we don't want to burn the pump up. I just don't think it's made to work like that.
So in a nutshell, by going to the soaker/drip hose, in 1.5 hours per day were irrigating the entire garden. And with the old overhead method, 1.5 hours would water 1/3rd of the garden, plus the beans and corn.