Many different species of plants can be planted via hydroseedixing a slope, but such mixes aren't typically using the same sorts of plants most often used as ground covers planted as rooted cuttings from flats/4" pots/one gallan cans. Hydroseeding still requires certain procedures and follow up care and watering/maintenance to be successful. If you were to plant fast growing wide spreading more shrubby plants to cover your slope, it may be competitive price-wise and give you more options of plant types. You may find it worthwhile to hire a landscape architect/landscape designer/landscape contractor to meet with you on-site, review your conditions/expectations/budget and advise you what makes the most sense for your yard. There are always trade-offs for any approach, and hydroseeding may/may not be a good option for you.

I have been doing a lot of research on plants that don't need a lot of water since we bought a 3 acre property in lake mathews, ca. Here's what I have so far...verbena rigida, creeping raspberry...both spread very fast and require little water. I will be buying these for our slopes. delosperma cooperi is similar to ice plant but very hardy and does not require as much water.... Ice plant requires a lot of water and its heavy. That is what we have currently and we will be replacing it with what I have written here. All our slopes have ice plant and we are trying to save water costs. So I will be adding those ground covers and adding water wise bushes and other plants. Snow in summer also sounds like a good plant to add. They say it spreads fast and it's very nice... I also want to add fremontodendron, it looks like a nice bush to add...since we have so much room... Any other ideas?

If you have worms, you are better off than me. The first thing I would do is mulch the heck out of it. Then when I planted, I would bareroot the trees to correct for girdling and j hook roots and also to prevent soil interface problems. I have also noticed almost every container tree/shrub I plant is planted too deeply in the pot and the trunk flare is covered. Keep that basal flare above grade. I work almost exclusively on hillsides and there are a couple issues to deal with. You really need to control waterflow. I like zigzag swales to slow down the water and make sure a lot gets into the ground. If you make crescents, remember that they will overflow with enouh water and you need to control that. Pick an overflow location by making a low spot in the crescent and reinforce that with rocks. Also remember that hills have great drainage so you will probably want a swale above the tree as well. That will give the water a place to soak in and then travel underground to the tree below.

Rather than using a solid cloth, look for jute netting. This is made specifically for erosion control purposes but is designed to plant through. It is affixed with staples just like the burlap cloth. There are various dealers of this product in the Seattle area. I am a bit concerned about the ivy roots remaining. When did you remove the ivy? Typically, English ivy will regrow from the roots rather easily and rather rapidly. It may make a great deal of sense to just let the ivy grow back. While it is not the best choice for slope stabilization, it apparently has been doing the job satisfactorily in your situation and I encounter it used for the same purpose in many other, highly sloped situations as well. I would be concerned that attempting to remove the root system - which you no doubt have determined is tenacious and widespread - will destabilize the slope even further. And you want to get this slope secured before we hit the rainy season. I do realize it is considered an invasive species and I would never suggest planting it but sometimes removing it causes more problems than it solves. If you do opt for the kinnikinnick, start with small (4") pots and plant directly into the native soil. This plant is native to this area and should adapt to our soil and climate conditions just fine. It will need some watering to get established and any low emission water source (drip or soaker) should work but be very cautious about over-watering and further weakening the slope. Luckily the kinnikinnick is not a very thirsty plant and won't need much water to get established. Don't bother mulching - it probably won't stay put and delays the spread of the GC's. In either case - leaving the ivy to regrow or planting with a new GC - use the netting to provide some degree of security until the plants fill in. May I be nosy and ask where in Seattle you are located? I've done a bit of erosion control work on various properties close to the Sound and even a landslide remediation project just south of Richmond Beach.