My guess would be not enough water and fert. Potted herbs need much more than their in ground brothers and sisters.

Under normal growth conditions, nitrate is mainly exported to the leaves to be assimilated but under conditions when N is in shortage, the transport of nitrate from the roots would be inhibited or greatly reduced. In addition, up-regulation of leaf metabolism of N is much slower than in roots when adequate supplies are furnished (when you fertilize). This is one of the reasons that a continual supply of N is so important in container culture.

Soil composition also has a substantial influence on N availability. E.g. if your soil has lots of wood products from sapwood instead of conifer bark, N might be unavailable because of an extremely high Carbon to Nitrogen ratio. Hardwood sapwood products have a C:N ratio somewhere in the vicinity of 1,000:1 while conifer bark is in the neighborhood of 300:1, providing much more favorable conditions for N assimilation.

Condensed version: A N scarcity causes plant growth to favor more roots than shoots.

Al

Thanks, to both of you. That answer surprises me. I mean, all I ever see in culture remarks about herbs is to make sure the soil is lean and somewhat dry. If anything, when I potted these up with bagged mix, I was worried that the soil would be too rich, and that I'd get rank growth and not very palatable herbs.

I don't recall the brand name of the potting mix (Miracle Grow?), but it was from a big box store. I figured the mix already had enough nutrients for a single season.

That answer surprises me. I mean, all I ever see in culture remarks about herbs is to make sure the soil is lean and somewhat dry.

The remarks you have read are accurate for most (but not all) herbs when grown in soil. There the nutrient levels are already high enough in most cases. It is true that most herbs do not require a lot of fertility and too much results in lots of leaf growth, but to some palates the flavor is inferior to plants grown in leaner conditions.

What I think you experienced is that you counted on the potting soil to meet the needs of the herb. Nitrogen (the macro nutrient that promotes vegetative growth) is the nutrient which is most easily depleted from containers because it readily mixes with water and runs out the bottom of the pot.

It is important to understand that in containers there are 0 nutrients and water. Even mixes that come with nutrients should be regarded as having none. Everything the plant needs is up to you in container culture.

There are a couple things you can try, but here is what I, personally, recommend for potted herbs. Others will have different ideas. First, mix your potting mix with compost. You don't need a lot of compost, but some helps. Let's say 10% compost. This adds nutrients in a low amount. In addition to small amounts of macro nutrients it also supplies the micro nutrients that plants require for optimal growth. The nutrients in compost can be considered slow release. they are made available to plants via biological activity which just means the plants get it as they need it. The nutrients are not as prone to running out the bottom of the pot.

This alone may be enough for herbs in containers. To ensure enough nutrients throughout the season though, use organic, liquid fertilizers like fish emulsion (available at any well stocked garden store). These are low dose ferts that will never 'burn' your plants nor will they result in a salt buildup. In addition to supplying macro nutrients, organic ferts like fish emulsion also supply micro nutrients. How often to use it is judged by plant growth. To start, use it once a month assuming you have some compost in the mix.

If you are growing annual herbs that will only be around for a single season you could get by with regular potting mix and miracle grow just fine as well.

Thanks.
I'll give them a try again, but with the compost/fish emulsion. Much more convenient to have some herbs in pots right by the door to the kitchen than to have to trudge out to the garden.
Colin

I'm not sure if I stand alone in my recommendation to forgo the addition of adding compost to container soils or not, but I never use it in mine. I'll state the reasons I disagree with the wisdom of using it in soils & then you can make up your own mind. Because it's readily available, inexpensive, and happens to contain some minor elements, doesn't make it a prime choice as a soil ingredient.

The small amount of micro-nutrients supplied by compost is far outweighed by its adverse effect on soil aeration. In the case of growing herbs, this physical feature of soil is extra important because of their tendency to demand good drainage, but it is important in all container culture.

We would do well to select a soil that is well aerated and maintains its aeration for the expected life of the planting. Aeration and its inextricable relationship with drainage should be a container gardener's first consideration and priority. Every other cultural consideration, light, temperature, water, and nutrients are easily manipulated by the grower. Move the container, add more/less water/nutrients & you can easily adjust these cultural conditions. Soil aeration is pretty much a done deal. It is what it is and progresses toward what it will be, regardless of what we do after the planting is completed. If you choose a soil that insures aeration you have a good chance of rearing a vital and healthy plant by properly manipulating the other cultural conditions. Give no consideration to aeration/drainage, and your efforts are more likely to be futile than productive.

Compost, already in an advanced state of decay, breaks down too quickly, clogging macro-pores & creating compaction. Seaweed emulsion is generally considered a superior source of the minor elements when compared to fish products and is much more effective at reliably delivering them than compost. There are also a number of other reliable products, both organic and inorganic that are more effective than compost at delivering the minors. For these reasons, I choose to leave compost to the garden & look to other components to satisfy soil requirements.

Al