With only a couple months left in the growing season I decided today's the day to check soil pH throughout the garden. I've had 6-7 months to watch which plants grew well and which flopped—like my watermelon and cucumber. Now I have to figure out why.
I planted my first crop of seeds at the end of January just to experiment with how early I can push the growing season. The answer is: not that early. There were too many variables working against the warm weather crops like tomatoes and squashes—short days, cold nights, strong winds, and critters that were hungry for fresh seedlings. I ended up planting several more rounds of seeds throughout early spring and summer and some of those plants fared much better. Others not so much.
This summer I visited Bellefontaine Nursery in Pasadena and asked owner Alan Uchida why some of my crops seemed stunted, even in perfect weather. My biggest concern was that I chose a bad brand of potting mix. To my relief, the brand I use is the brand Alan recommends (Kellogg/G&B). He helped me load my car with bags of earthworm castings and top dressing and suggested I monitor other factors that could be affecting growth. By the way, the Uchida family has been in the nursery business for generations. Their shop only closed for a few years during World War II when the family was sent to Japanese internment camps. Read their inspiring story here.
After months of monitoring the garden here's what I've discovered in my first year:
The position of the yard, position of the house, and location of large trees on the property create microclimates. There are pockets of shaded cooler still air and other areas where plants are blasted with hot sunny Santa Ana winds.
The soil composition varies greatly throughout the property from decomposed granite and heavy clay to sandy loam and lawn areas previously amended with topsoil. The wind makes surface soil dry very quickly, whereas deeper clay soils have drainage issues. The soil pH is fairly neutral, but many planting areas are too alkaline.
Every gardener seems to recommend mulch everywhere so that's exactly what I did this year. That is, until the Argentine ants made the mulch their home and attracted ants into our house. I'll be writing a future post all about those invasive mini monsters. But for now, I've scraped away much of the mulch from planting areas nearest our home.
Critters will always be a challenge. Those Argentine ants also create colonies around root balls that have killed some of my ornamentals. Pocket gophers pull roots and shoots down into their tunnels. And then there are the squirrels, birds, mice, aphids, squash beetles, citrus scale, hornworms and leaf miners. Not to mention the coyotes who will stop at nothing to get at a fresh batch of stinky compost.
To me the joy of gardening still outweighs all the frustrations, so I just take it one headache and harvest at a time. Today's problem is pH...
A neutral pH reading is 7. That means the soil is neither acidic nor alkaline. A pH reading lower than 7 is more acidic, whereas a pH reading higher than 7 is more alkaline. Typically when you purchase an all-purpose potting mix or garden soil blend, the manufacturer takes pH into consideration and you'll often get a product in the 6.0-7.5 range. Because I blend my potting mixes and soil amendments with the native soil on my property, the pH varies from pot to bed.
To test pH I use an inexpensive and simple three-way meter like this one from Amazon. Simply stick the dual probe into the soil, wait a few seconds, and the needle will display whichever reading you're seeking: pH, moisture, or light intensity.
Okay, I just said "probe" and "three way". I'm not above taking a moment to appreciate the art form that is juvenile humor. Who's with me?
Anyway, with this gauge I was able to determine which plants were not draining well deep around the rootballs, despite their having dry topsoil. Without careful monitoring, those plants could easily die from a soggy bottom.
For my soils with higher pH (alkalinity) that require more acid, I'll be incorporating more decomposed/decomposing organic matter in and around the soil. Top dressing with fallen leaves, mulch, and compost will gradually decrease pH. Some gardeners add vinegar or citrus juice. I have an overabundance of unused citrus from my lemon and grapefruit trees so that will be easy.
Gardeners who are comfortable using amendments can use garden sulfur to decrease pH, like Espoma's Soil Acidifier. Many fertilizers are also formulated for acid-loving plants, so the addition of sulfur may not be necessary. It can be difficult to sustain the pH level your more acid-loving plants prefer because you're working against the natural components of the soil as they gradually dissolve. As this helpful article suggests, you might finally be better off growing your plants in a container or different location.
Regions like Southern California that get little rainfall tend to have soils that are alkaline (high pH). Rainy places have higher acid in their soils (low pH). If you've ever been to the Pacific northwest (Portland, Seattle) where rain is prevalent, you'll see acid-loving azaleas thriving.
If your soil is too acid for the plant you want to grow, lime, wood ash, and oyster shell are recommended for raising pH. According to this article, signs of low pH include stunted growth and yellowing of foliage.
So that I can compare soil changes from year to year, I'm posting today's approximate pH readings below. If you're into that sort of thing, you'll notice that most look okay whereas a few are off like my orange tree, avocado, fig, macadamia, and gardenia. Check out this Farmer's Almanac article for a list of plant pH preferences.
My next step is to send soil samples to my agricultural extension office so that I can obtain a more comprehensive soil analysis, including salt concentrations. With very little rainfall in SoCal (and because I don't use automatic irrigation) salts can accumulate in soil—something I'm currently concerned about with my four avocado trees whose leaves have shown brown tips (salt burn?) the past two summers. This NPR article explains why California growers are so concerned about salt.
Bottom Line: If your plants & trees aren't thriving there are a few basics to check on before digging any deeper: pests, watering/drainage, nutrition/fertilizer, soil pH, and light.