Last year I planted curly kale in a large container. The soil used was 60% purchased organic soil and 40% purchased organic fertilizer. What should I add to the soil before planting this year? I have a good quantity of homemade organic fertilizer. How much should I add? Anything else? Can I plant kale in the container again or is it better to plant a different leafy green? Lastly I had aphids on my kale last year. Should I have any concern the soil could have aphids eggs in it?
Thank you for your help!
Outside United States
Brassicas like kale can have issues when repeatedly planted in the same soil year after year. Ideally, you would want to rotate crops with other plant families. You could substitute lettuce or spinach for kale in that case. Usually when people plant in containers instead of in-ground space is a consideration. Hopefully, you can rotation from pot to pot between families.
If you can't rotate the kale to another pot could be fine to grow kale in the same pot with the same soil but the more times you do that the greater the risk of a problem.
if you are replacing the soil in that pot, it's good sanitation practice to wash the pot in a 5% bleach solution to disinfect it. That would allow you to reuse the pot again and again, but it can get expensive if you have many pots you are replacing the soil in year after year.
Aphids often lay eggs on alternate hosts - usually perennials - to over winter so the soil shouldn't be too much of an issue as far as aphids are concerned.
The fertilizer question is a little more difficult to answer. Not know the nutrient analysis of the fertilizer or the nutrient content of the soil in the pot I can't give you a hard and fast answer. I can tell you that if you used organic potting mix (peat based) instead of soil (dirt based) you will likely need some fertilizer, though the fertilizer demand from kale is low.
That was very helpful. Thank you.
Is there a simple method for a layman to test the nutrient quality of the soil?
Most of the home kits are not very specific. You could go ahead and plant, then if the kale starts showing signs of deficiency or poor growth fertilize lightly. Kale usually doesn't need much. We never fertilize kale in our demonstration garden, but do amend the soil with compost prior to planting.
If you really want to have a good analysis, depending on where you are, you may be able to get your soil analyzed by a government or private lab. If you're close to the US border you might even be able to get one of the US extension services to do it.