It will contradict many long held beliefs and an ocean of instruction and tutoring, delivered in books, magazines and most everywhere else.
Today’s column is for the advanced gardener. That said, you may want to stop here and read no further. Proceed at risk; the risk of turmoil in your garden convictions. Continued reading will leave you with questions, not answers.
In gardening, as in many fields, it is easy to make sweeping statements. “Water in the morning”, “Plant in the fall”, “Fertilize regularly”, “Provide good drainage” and “Add organic matter” are common declarations that are drilled into a gardeners psyche from the inception of plant cultivation. Eventually, sweeping, repeated statements become truisms, adhered to without question.
But at least one of these truisms is becoming less true – in specific instances.
For the past several years the gardens of southern California have been drifting toward Mediterranean plant palettes. Boxwoods are giving way to lavenders, birch trees to olive trees, ivy to rosemary and foxgloves to salvias. Subtropical plants are yielding to desert plants. Agaves and aloes abound. California’s native plants have migrated from wild hillsides and into our gardens. Although this garden evolution (or revolution) is subtle and in its early incarnations it throws into question a long held gardening truism, “Add organic matter”.
If you’re still reading and prefer the simplicity of blanket statements, it is at this point in the column that you’re going to become confused and bewildered. Turn back now – please.
Let me break down the statement “Add organic matter”. For the huge majority of plants that we have historically cultivated in our local gardens this is a very accurate statement. If you’re planting roses, geraniums, tomatoes, petunias, camellias, star jasmine and thousands of other plants that are accustomed to rich organic soils, lots of summer water and high fertility, stop reading. Keep adding mulch, compost and planting mix to your soil – lots of it. In fact double what you’re now using, especially as surface mulch; it probably isn’t enough.
But, if your plant choices have drifted toward plants of Mediterranean origins and from arid climates, the addition of organic matter may not be the way to go. In fact, a rich loamy soil, full of compost, may by quite unhealthy for these plants.
Most truly Mediterranean and arid climate plants prefer “lean” soils, those that are low in organic matter and low in fertility.
Confused yet? It’s going to get worse – don’t say I didn’t warn you.
The danger in a discussion of soil and plants is that Mediterranean plants installed into clay soils have as much chance of survival as a California oak in an Amazon rain forest.
Recently, I installed a new succulent garden at my home. Into the area, about ten feet by twenty-five feet, I added 46 hundred pound bags of sand – and no organic amendments. The sand that I added wasn’t just any sand; it was #16 silica sand, a very specific type. Only very coarse “sharp” sand should be added to clay soils. All-purpose sand or builder’s sand will create a huge mess in your soil. I know you’ve been told repeatedly, “Never add sand to clay soil”. Don’t believe everything you hear; we’re destroying some “truisms” in this column.
The soil I was heavy clay when I began. I blended the sand very thoroughly with about four to six inches of the soil and planted. Good soil for a succulent garden, lean and well drained.
I’m preparing another area for low water shade plants and I just finished adding another 20 bags of the same sand. This fall, if my back holds out, I’ll prep another area where I plan to blend native and Mediterranean plants. I’ll be adding a lot of decomposed granite for this project, and again very little, if any, organic amendments. Just what these plants want!
In a separate portion of my garden I’m growing subtropical plants; lots of epidendrum orchids, bromeliads and cane begonias. In these beds I used no sand, they were filled with almost pure organic amendments to create a very rich soil suitable for what these plants want.
If you’ve made it to the end of this weeks column and are more puzzled that when you began, don’t say I didn’t warn you. The lesson of this week’s column is to match the soil to the plants. Plants that need rich, organic soils should get exactly that, plants that want lean soils should also get what they want. Simple as that. Beware of sweeping statements.
Ron Vanderhoff is the Nursery Manager at Roger’s Gardens , Corona del Mar.
Questions from Readers July 4th.
Question: Do I still have time to plant pumpkin seeds in time for Halloween?
Mary, Newport Beach
Answer: Hurry. In Orange County I usually suggest that pumpkin seeds by started no later that July 4 for Halloween fruits. It this time I would suggest either buying started plants or growing a smaller fruited variety, such as ‘Sugar Pie’, ‘Orange Smoothie’ or ‘New England Pie’.