Growing vegetables in containers presents a number of challenges for the urban gardener and following water, the most important is the need to feed your crop and more specifically, to feed it the right nutrients at the right time.
Sadly, I don’t believe that for a kitchen garden it’s really good enough to broadcast a slow release general fertilizer at the beginning of the season and have done with it. Ignoring for the moment my decided preference for organic and naturally sourced fertilizers, lets just look at why a slow release general purpose fertilizer isn’t good enough.
There are a few issues to consider. The first is about how much nutrient any one plant needs at different stages of growth. Another issue is about the right nutrients at the right time and the final issue I’ll talk about is what happens when crops with different needs are planted together or why in this instance tomatoes don’t love basil.
Vegetables need different levels of nutrient depending on their stage and rate of growth. Who eats more, a 40 pound child or a 240 pound adult? I’ll bet you can easily figure out the rest of this point- a seedling tomato does not require the same volume of nutrient as a mature vine in the heat of the summer covered with ripening fruit. Yet the role of a slow release fertilizer is to make available a finite supply of nutrient in a steady stream and it’s not that it will sit around and wait. The problem is complicated by the fact that one of the reasons that containers need to be fed is that there is a constant flushing away of nutrients as watering and rain washes through the growing medium. So while you’ll have lots available for the young growing plants, once you’re setting and growing the fruits of a tomato (for example) you will have pretty much depleted the reserve.
And even if it hadn’t been depleted, it wouldn’t be right. Early growth is vegetative – and uses what I call the green food. The priority is leaves, stems and good roots, but as the season progresses, if you want to see a bumper crop of tomatoes for example, you need to change the balance of food to support the abundant production of flowers and fruit.
But then again, not all vegetables produce fruit. Think about the leafy greens like lettuce and spinach and your herbs like basil, which are an important part of any kitchen garden. If anything you would like to with hold the nutrients that boost flower production, because for these plants flowering, quite literally, is the kiss of death! If you don’t believe me, nibble on a lettuce leaf from a plant that has flowered. Just be prepared to spit it out really fast because now you’ll have a whole new appreciation of bitter. A general purpose, slow release fertilizer, even one that claims to be formulated for kitchen gardens is a compromise. It will have proportionately too much potassium for crops that you don’t want to flower and not really enough for crops whose final yield is inexorably tied with their ability to flower and set fruit.
Another big challenge with container kitchen gardens and feeding them properly is that when you combine two plants with different nutrient needs, like basil and tomatoes, in a single container, the food that’s right for one late in the summer will ruin the other.
What’s the solution? To get the best production from your container kitchen garden, you need to adjust the food throughout the growing season and take into account not only how big your plants are, but what you want (and don’t want) them to do.