Soil amendment, was Planting Lilies

Jane McGary
Sun, 17 Feb 2013 10:59:19 PST
Gene wrote:
>If you garden in heavy soil, it might be better to transplant in 
>Fall, before the soil gets too wet and cold.  Another strategy is to 
>make raised beds in Fall and cover them with plastic.  That keeps 
>the soil in perfect condition for planting all Winter long and into 
>Spring.  But I think the best plan is to improve heavy clay loam 
>soil with lots of coarse sand.

Before readers go out and mix whatever sand they can get into heavy 
clay, I'd like to add this. The crucial word in Gene's note is 
"coarse." This means sharp, angular  particles of various sizes. If 
your sand comes from a low-elevation river deposit or worse yet from 
a beach, it is likely to be too fine and the particles too rounded to 
be a good soil amendment. Another crucial word in his note is "loam." 
That is, the clay-based soil already has a fair amount of organic 
material in it. If you mix sand into a really sticky clay, like 
adobe, you'll get something that feels like lumps of chewing gum with 
sand stuck to them. (I made that mistake in my mother's central 
California garden once.)

After a quarter-century gardening on gritty upland soil, I recently 
moved to a lower elevation and confronted heavy clay loam. Except for 
the bulb house and rock gardens, where I created deep beds of coarse 
sand and other well-drained components, I had organic amendments 
tilled in deeply after the existing sod and trash shrubs had been 
removed. My lilies and other moisture-tolerant bulbs went into the 
prepared beds and, as Gene suggests, were mulched with a mixture of 
milled compost and well-composted fine bark (available by the 
truckload from a nearby supplier). I had the coarse sand brought from 
the quarry that supplied my former garden: it's high up on a 
rivercourse and is very sharp and gravelly. The extra haulage was 
well worth it. The top 14 inches (35 cm) of the raised beds in the 
bulb house is pure coarse sand, on top of about 6 inches (15 cm) of 
clay loam with a little well-composted manure added. A woven 
groundcloth barrier is below that. After planting the bulbs I mulched 
the surface with pea gravel and quarter-ten crushed rock. Everything 
seems to like this, but I have to add nutrients via soluble 
fertilizer; they got their first spring feed yesterday.

I have been wondering whether to add more mulch to the main lily bed, 
but am hesitating because I interplanted the lilies with hybrid 
peonies. Can someone advise whether peonies tolerate an organic mulch 
over the crowns? I have always avoided it. I suppose I could leave 
the peony crowns uncovered, not difficult as they are under wire 
supports, and just add mulch to the rest of the surface.

Thanks also to Gene for mentioning that late winter is an acceptable 
time to transplant seedling lily bulbs. I have some crowded pots of 
them that I should have dealt with last fall. I'll keep them in large 
pots in a shaded area this growing season and plant them in the 
garden next fall.

Jane McGary
Portland, Oregon, USA

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