Hi @tmcgahey … that’s great you’re doing your part to reduce water usage. I have a similar spike for deep watering but mine has a perforated cap at the top to take in excess surface water like when we get a heavy rain, typically after I’ve washed my car.
It’s just fine to irrigate through the spike but you should also have drip emitters at the surface. Emitter count and flow rate are important but grouping your trees by water usage plays a bigger role towards efficiency. For example, Laurel and Crape Myrtle are high water users and should be on the same valve while Ash, Olive and Pistace are medium to low water users and ideally grouped together. Your Oak and vitex are low water using once established. For any of your trees adjacent to your lawn, you can very likely eliminate supplemental drip irrigation once they are established.
I’m not a fan of inline fertilizers for residential properties. Your plants need more water in order to process fertilizers. So adding fertilizers to the mix is working against your conservation goals. Unless you’re harvesting crops, you don’t need your plants to grow; you want them to stay green. When you do need to fertilize, you’re better off with a watering can so you can monitor application. And honestly we’re talking once a year, if at all.
I know lawn can be a challenge in the desert but that’s another area I would reduce or eliminate fertilizers, especially if your turtle buddy is chomping on the grass. When I had a lawn, I rarely fertilized it. I used a reel mower and let the clippings call back into the grass.
For improved water conservation, you’re better off focusing on soil health. Commercial fertilizers are often harmful to the insects, microbes and other critters that make up a healthy soil biome. Instead transition to natural mulches and yard clippings. When you have a healthy biome, the soil becomes better aerated increasing the ability of the soil to take in more water. You’ll have healthier roots and happier trees.
I’m in Southern Nevada. My mesquite and Texas Mountain Laurels have not been watered in five years. I have a Bookleaf Mallee that does not have any irrigation and is growing like a champ. It can be done!
I hope that helps. Good luck with your conservation goals!