Growing in a Greenhouse
Answered by: Inge Poot
Question from: Beth Howie
Posted on: April 4, 2001

I am a gardener at a private estate along the coast of Maine, USA. Aside from our everyday tasks of tending to the gardens, we grow herbs for the owners. Our herbs mainly consist of dill, cilantro, basil, parsley, sage, rosemary, thyme and oregano. Not knowing at what time the owners will arrive in the summer months forces us to sow herbs weekly starting in the spring and throughout the summer months so to have the "perfect" pot of each herb to bring to the estate when they arrive.

I have found through and experience and have verified it in reading your Q&A section that dill, cilantro and parsley do not transplant well but since our herbs have to end up in 6" standard clay pots we usually have to transplant since direct sowing in the pots usually does not produce a strong plant. I’m writing in hopes that you can give me some tips on a good soil mixture and a way to grow these three herbs in particular to be strong. We have a greenhouse specifically for the herbs, we are trying to become organic growers, and we also have space for growing the plants outside in our vegetable gardens. Any helpful tips you have are greatly appreciated.

P.S. in the past we have used pro-mix, lime and some compost added to our mix and have fertilized with miracle grow. This year we have begun incorporating more seaweed fertilizer into our fertilizing.

Addressing your growing mix problem first: Your mix may be too humus rich and would probably be improved by adding some gritty sand to the mix to get sharper drainage. Fresh pro-mix already has some slow release fertilizer in it and therefore does not need any fertilizing for about a month. If you over-fertilize herbs you will get lush, weak and poorly scented foliage.

Your plants will have sturdier growth and better flavour if you move them into your vegetable garden as soon as temperatures stay above freezing. Plunge them pot and all in the soil, so that they can be lifted when needed without any set-back. I presume your climate is moderated by the sea and the plants won’t have to contend with blistering heat or other climatic extremes. If this conjecture is wrong, it may be better to leave the plants in the shelter of the greenhouse, but make sure they get as much sun as possible- their origin is the Mediterranean and they love sun.

Of the plants you mentioned, only cilantro would have to be renewed every two weeks. It is a very short-lived annual and can go from seed to seed (followed by death!) in two or three weeks. Keeping it cool at no more than about 15 degrees Celsius (60 degrees Fahrenheit) keeps it in the vegetative, lushest stage a bit longer. Also make sure to nip off flowers to prolong its life. You might wish to try the two perennial corianders we offer for a long-lasting pot-plant. Their flavour is very similar to the annual plant, but they only need frost protection to last for many years. The Vietnamese coriander is one of the few herbs that prefers half sun and evenly moist soil. The bristly leaved Mexican coriander will even stand a bit of cooking without losing its flavour, but it needs to be chopped very fine to be used fresh as a garnish.

Parsley should give you no trouble if you grow it cool. It languishes in heat and in such a situation may not come into its own until cool fall days arrive. If for direct seeding you plant about 10 seeds in a small circle near the center of the six-inch (15 centimeter) pot and pull out all but the three strongest seedlings, they should -under cool conditions - form a bushy pot in about 8 to 10 weeks after germination. Germination, as you know, may take 2 or more weeks. We have found that the seedlings transplant quite well if done just as the first true leaves emerge. The tap root is not very long yet at that time and with gentle handling can be moved without injury. You probably know that at that stage the seedling is so succulent and brittle that it is best to only grasp it by the cotyledons (seed leaves). The plant should last at least a year. It will eventually grow a bloom stalk at the expense of leaves and should be replaced at that point.

The other plants you mentioned are all perennials and will not grow very much for the first 6 months and will get much more vigorous during subsequent years. An early start is essential to produce a harvestable plant by summer.

The pro-growers section of our web-site should give you lots of further good hints on timing your crops.

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