Watering once a week isn't really minimal watering, esp. for Ceanothus. Give them a good start by planting in late fall-early winter, soak them really well and let the rains take over. Deep water them about once a month the first summer, avoiding the trunk of the plant, and no summer water after the first year. It's also important to choose varieties that work in your zone. C. horizontalis is more coastal I believe and thrives in cooler summer temps. I've found that many ceanothus need some afternoon shade in the more inland areas Type your zip code into Las Pilitas web site and they should give you a listing of what will work in your area. Also check out the "Design" link at the top of the page for useful info on watering and other subjects http://www.laspilitas.com/easy/easywatering.htm Here is a link that might be useful: zip code plant communities

Well, thanks for your feedback everyone, I am still undecided, I really do want it to be a dense screen. What is the worst that could happen if i space them 7 or 8 ft apart rather than 10 ft? I am thinking this way to be cautious because they do have to put up with a bit of competition near the property line from the neighobors established prunus, so I want something vigorous. thanks , if anyone has more feedback.

I planted two of that variety about 18 years ago and both are gone now. The first one went within the first 7 years and the last one declined over a longer period of time finally falling about two years ago. I live within 1/2 mile of the ocean, which I think is probably what did them in. They were easily trained into trees by cutting back the "weeping" foliage, but it was a constant chore to keep them upright. One of the best things about the them was that they afforded me the opportunity to observe a woodpecker up close quite a few times. The pattern of holes they made on the trunk and limbs was one of the most beautiful things I have seen. It really pained me to stuff those into my woodstove.

For those of you planting Ceanothus, DO NOT amend the soil with compost or any other nutrient. Ceanothus are genetically-designed to live in nutrient-poor soil. They get their nutrients by forming symbiotic relationships with frankia bacteria in the soil. Frankia attach to the roots and provide the lilac with nutrients, water, and protection from pathogens. The bacteria get carbohydrates in return. Adding nutrients causes the Ceanothus to drop the fankia from its roots and leaves the plant open to attack from pathogens. You can establish a good frankia population in your soil by mulching heavily with pine, fir, redwood, or oak bark (chips or shredded). If you have poorly-draining soil, amending the soil with rocks or sand will usually create a mess. Keep in mind that water will drain via the path of least resistance. If you have thick clay surrounding a heavily-amended spot, water will drain into your amended area and your plant will end up living in a bathtub. (Also, mixing sand and clay will form a concrete-like substance that won't drain.) At minimum, you would have to amend a very large area (like 6' x 6' x 2' deep), as plant roots tend not to travel from one type of soil into another. And even then, getting it to drain well will be tough. If you have clay soil, select a Ceanothus that will tolerate clay and plant in a sunny spot with the crown of the Ceanothus 1/2" above ground level. If you mulch a couple of times a year, the mulch will naturally break up the clay and improve drainage. Water lavishly upon planting and perhaps once a month for during the first summer (water around the perimeter of the root ball, try to keep the crown dry). They'll do best on natural rainfall afterwards. If you're in a bad drought year, give the Ceanothus a couple of extra waterings in the late winter/early spring.