Want Fruit? Good Sun, Not Too Much Fertilizer

cluster of grapes, Sherman Oaks, July 8, 2014Recently, someone asked me about a grapevine, planted three years ago, that has yet to produce fruit.
”What’s the problem?” our would-be vintner asked in a combative voice.
If this person were more experienced, such a question probably would not be asked. Experienced cultivators of the earth know that there is no point in questioning the whims of Mother Nature.
If that vine is meant to produce fruit for this gardener, it surely will. If not, all the care and chemicals under the sun will not make a difference.
In fact, chemicals – in the form of nitrogen – could be inhibiting flower and fruit production on this vine. In any plant, excessive nitrogen – an element found in nearly all fertilizers – prevents growth of flowers. Without flowers, there can be no fruit.
Plants produce both vegetative growth (leaves, shoots, roots) and reproductive growth (flowers and fruit). One type of growth will occur at the expense of the other. When grapes or strawberries or tomatoes produce lush foliage but no fruit, the reason could be an overabundance of nitrogen in the soil.
Once a tomato or eggplant or squash has produced flowers, it need not be fertilized. Such treatment might detract from maximum flower and fruit production. In vegetable plots, as long as nitrogen – whether in the form of well-rotted compost or granular lawn fertilizer – has been worked into the soil prior to planting, no further fertilization should be necessary.
Insufficient sunlight, as most of us know, also will inhibit flower and fruit development. Yet there is a connection between lack of sun – or a shady microclimate – and uptake of nitrogen in a plant. Often, the less sun a plant receives, the greener its leaves, indicating increased nitrogen uptake under these conditions.
Even a plant growing in enough light to form flowers will not do so unless it has reached its proper, critical flowering size, which is different for each species. A plant raised from seed does not flower when it reaches a certain age, but rather when it attains a specific size or bulk or height. A plant could be 100 years old but – if kept short by constant pruning – without a single flower in its history. Plants that once flowered in the garden but were drastically pruned back may take years until they flower prolifically again.
Many fruit trees and vines – plums, apricots, apples, avocadoes, grapes – have a tendency toward alternate bearing. This means that they produce heavily one year and sparsely the next. The reason for this has to do with striking a balance between vegetative and reproductive growth; heavy fruiting takes a lot of energy out of a plant and it may need two years to accumulate enough reserves of sugar and minerals to fruit that way again.
A prerequisite for growing edible plants – or any plants, for that matter – is patience. A vegetable crop that is supposed to take 90 days from seed planting to harvest may take 120 days or more, if the weather is unusually cool. A fruit tree or vine that the nurseryman said should be cropping well after three years may take six years to produce as advertised.
If you have doubts about the aesthetic value of an ornamental shrub, just leave it alone. After two or three years of unrestrained growth, you may see qualities in that plant that you never thought it possessed. One of the benefits of visiting a botanical garden is the opportunity to see plants fully grown.
It remains to be seen if the urban gardener can develop the proper attitude for growing plants. In our perpetually impatient freeway frame of mind, can we yet learn, somehow, to give plants their due?

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