Fertilizing Container Vegetables

(Question)

I’m experimenting with growing vegetables in containers this year – tomatoes, sweet peppers, lemon cucumbers, scarlet runner beans. I made my own potting soil using peat moss, perlite, and a little pit of compost along with some slow release fertilizers like blood meal for nitrogen, bone meal for phosphorous and lime to balance the PH of the peat moss and add calcium.

All containers are watered in the evenings and receive sunlight all day long. They have been getting a half dose of quick release fish fertilizer about once per week.

The plants all started off doing well, but fruit production seems a bit limited, the tomatoes being the only exception. I have only a few cucumbers and many of the leaves on the scarlet runners are going yellow and dying. Are these watering issues or fertilizing issues?

I have no idea how much to fertilize in extreme hot weather. All the literature suggests more fertilizing for container gardening, but Jeff Gillman who wrote the book “Decoding Gardening Advice” says to stop fertilizing in extremely hot weather as the salts in fertilizers make the water less available to the plants. In summary, when it comes to fertilizing what is a container vegetable gardener to do?

Thank you for your time.

(Answer)

I think you should cut back on the fertilizing, not just because of the hot weather, but also because of the amount of product in the initial container mix. I generally recommend (and use) one part compost to two parts commercial container mix.

If the plants are stunted and yellowing, that could indicate a nutrient deficiency, but it seems as though they grew well but just fail to bloom and set fruit. That could be because of too much fertilizer.

However, I agree with your thought that the watering regimen maybe the issue. With a very peaty container mix, it is easy to think that you have watered well because the top is moist. But digging down, you may find that the soil surrounding the plant roots is completely dry. Once peat is dry, it actually repels water, so you may not be achieving anything with your nightly watering.

Both cucumbers and bean require consistently moist, pliable soil.

You may well need to water twice a day in extremely hot weather. Water until water runs out the bottom of the pot but don’t let it sit in a sauce of water. Dry peat will cause water to run off down the inner sides of the pot, so may sure you dig down to make sure the soil is moist all the way through, then maintain it so.

Of course, yellow leaves may also be caused by root rot due to overwatering … the inner soil should be moist but not dripping.

Beans are also susceptible to fungal diseases, so make sure you are watering the soil, not the leaves, and ideally, water in the morning and, if necessary, in the afternoon, as opposed to evening, so the leaves are not wet all night.