Re. Flat terrain, heavy clay soils, and slow drainage

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Thanks Sean, Margaret, and Karrie for your input!

Looking around the garden, I realize most of what I've planted has done OK, though I've been pretty conservative with plant choices (for wind, drought , frost, arid air). When we first moved in I brought in about 20 yards of shredded hardwood mulch, and I put in some perforated flexible drains in the low spots. I wish I'd known the importance of raising the grade in planting areas, as only a few inches in elevation can make a huge difference, and that can't be changed after planting trees and shrubs. Now I use most of the garden's green waste as mulch, and I've been periodically applying pelletized gypsum and chelated iron.

My most glaring failures have been citrus, 3 of which were happy in pots from our old house, but once were planted in the ground slowly died.  Leptospermum 'Ruby Glow' also has done disastrously:  I have four left out of fifteen shrubs planted.  Viburnum tinus 'Spring Bouquet' has also died on me, and Arctostaphylos don't belong: the Howard McMinn's have leaf burn (probably salts) and half of the A. edmundsii have keeled over as well.  

An Acacia subporosa is unhappy, but I think it's suffering from seepage from our uphill neighbors.

But the successes far outweigh the failures, and for a 3.5-year-old garden, I'm not too disappointed.  The dominant trees are Melaleuca quinquenervia for screening and Olives for shade, and they've done very well, as has a Parkinsonia, Fig, Pomegranate, Arbutus unedo, and several Toyons.  A young Quercus tomentella looks good so far, I just keep my fingers crossed.

Among shrubs, Ceanothus cultivars have been very successful, as have Cistuses, Lavenders, and Rosemary, though some of the Cistus and Lavender on flat flat ground have been short-lived.  The Cistus look like they may have been root-bound though.  Euphorbia characias wulfenii (does this have a shorter common name?), Limonium perezii, Kalanchoe pumila, Aloe striata, Hesperaloe parviflora, Erodium reichardii, Heuchera, Roses, Narcissus tazetta, Tulipa clusiana, and Agapanthus are all very happy.

I'm thinking about planting a couple of Canyon Oak, Quercus chrysolepis: does anyone have experience with this one in heavy soil?

Thanks!

-Ben Armentrout-Wiswall

Simi Valley, CA