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Nicole 11-24-2015 11:36 AM

Watering dilemma for new plants in clay soil
I am new to gardening, especially with natives, and my husband and I have spent that past 6 weeks installing new hardscaping and planting nearly 100 natives in our yard. After all that work I'm very nervous about over/under watering while getting the plants established. We're in Los Angeles, Sunset Climate Zone 22 (but only a few miles inland from the coastal zone 24). I've consulted every source I can find, but much of the information seems contradictory for my specific situation. These are the guidelines I am trying to follow:
1) Water deeply and infrequently to encourage deep roots
2) Wait to water until the top 3-4 inches of soil are dry
3) Keep the root ball moist for at least the first 2 months after planting
4) In general expect to water about once a week, but will vary based on soil, sun, climate, temperature, etc.
5) Water the area around the plant, don't just soak the root ball to avoid root rot.

Here's my dilemma:

So far I've been painstakingly hand watering, giving each plant 4-5 gallons at a time taking extra care to avoid run-off. We're using 2-3" of bark mulch to keep the soil cool, retain moisture, control weeds, and prevent a crust forming on the top of our clay soil so water can penetrate easily. That's working wonderfully, but since we've made sure to keep the mulch a few inches from the crown, the root balls and the well-draining soil they were potted in are mostly left exposed to the sun and wind (although we are using nurse rocks for many of the plants). This is causing the root balls to dry out while the surrounding soil (even an inch or two out from the root balls) remains very moist or even wet 10-14 days after watering for full sun/part sun areas and 14 days or more for shadier areas. I am using a moisture meter to test the soil and so far it seems pretty accurate. In all of my research I've only managed that find two sources that mention this is likely to occur with clay soil, but no specific advice for what to do when it does. Given the guidelines listed above, these are my questions:

1) If the root ball is dry but the surrounding soil is very moist/wet, should I water?
2) If I water, should I just water the root ball or the surrounding soil as well?
3) If I just water the root ball, how much? The same 4-5 gallons to water deeply, or just enough to keep it moist until the surrounding soil dries out more?
4) If I water just enough to wet the root ball, will this prevent deep root development?

So far I have been waiting for the surrounding soil to dry to at least moderately moist before deeply watering the root ball and surrounding soil. This has been an average of 10-14 days between waterings. Overall the plants appear healthy and most are showing new growth. I see very few signs
of stress and only minor pest damage on a few, but it's only been a few weeks. It's also my understanding that what's happening below ground right now is most important for establishing drought tolerant plants. I realize this is a very long post, so if you're still reading- thank you! I appreciate any advice you have to offer.

Lastly, here is a list of the plants we chose:

Island mallow (lavatera assurgentiflora), Indian mallow, monkeyflower, compact Cleveland sage, penstemon Margarita BOP, island bush poppy, coyote brush, Skylark ceanothus, wooly blue curls (trichostema 'Midnight Magic'), Douglas iris, gum plant, seaside daisy, lilac verbena, lemonade berry, hummingbird sage, woodland strawberry, bush anemone (carpenteria californica 'Elizabeth')

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