From a Correspondent:
My wife and I are fairly new to growing vegetables here in the desert. I've read nearly every book I can get my hands on and noticed a couple things that got me wondering.
1. Is foliar feeding really effective for plants? Seems to me that with the heat so much of what I spray on the plant would get evaporated before the plant has a chance to soak it up. Some of the information I've been able to dig up on the Internet suggests that the plant can get many times more nutrients from it's leaves than it can from the ground.
2. How can I tell if I have caliche without digging down the 4-5 feet recommended by some of the desert gardening books? We plan on planting some fruit trees in our yard this winter and want to give them the best chance for survival, but don't want to just dig down 5 feet unless I really need to.
Good morning, Tom,
These are both great questions. The answer to both is: it's all about the soil. But since they're from different perspectives, I'll answer your first question here, and the second in a following post.
Foliar application of fertilizers pops up every now and then as "the" answer to gardening, sold primarily on being fast. Fast, however, isn't really our goal in home vegetable gardening. If we were really looking for fast, we'd just pop down to the grocery store and load up the cart with produce. That's much faster.
More to your point: I would suspect, though I have seen no studies to back it up, that evaporation would tend to limit the availability of the fertilizer to the plant. And — because all fertilizers are salts — that leaves us with a residue of salts on our plants' leaves, which seems unwise.
On a — literally — deeper level, though, there are greater problems with foliar feeding. First is the name: even though we talk about "feeding"our plants, and foliar "feeding," the truth is we don't feed plants. Plants create 100% of their own food through the process of photosynthesis. Real plant food, despite advertising to the contrary, is made up of sugars and starches created within the cells of the plants. The elements of fertilizer — nitrogen, phosphorus, potassium, iron, sulfur, magnesium, etc. — are simply among the elements that plants use in the creation of their food. They are not food itself.
Which brings us to your next point: while it is possible that plants may be able to absorb many times more nutrients through their leaves than from the ground, I have my doubts about this, having seen studies on both sides. But what we do know to be fact is that plants can absorb from the soil all the nutrients they need. And excess beyond need, is, well, excess.
So, to cut to the chase: gardening, especially vegetable gardening, is all about good soil. And foliar feeding does nothing to develop good soil. Save the money that you might have spent on foliar fertilizer and invest in organic soil amendments instead. Compost is excellent, as is rotted cow manure. Organic soil amendments will add nutrients to the soil, improve water retention and drainage, increase the levels of biotic activity in the soil, probably decrease pH levels — which will increase nutrient availability — and in general be beneficial to your plants.
Spraying foliar fertilizer may give a plant a one-time boost, but incorporating organic materials into your soil at the beginning of every planting season will consistently and continually improve your soil over time. And it's really that improved soil that will give you a good crop of vegetables. If in the future you suspect that you have a deficiency of a particular element — nitrogen, for instance — then side-dress your plants with an organic fertilizer applied to and worked into the surrounding soil. It may take longer to benefit the plant, but it will also have a longer-term benefit to the soil. And that's really the whole secret to growing vegetables in the Desert Garden.
I hope this helps,