Rosemary Specifics for Newby Growers
Answered by: Conrad Richter
Question from: No Name Given
Posted on: December 4, 1999

I read all your previous Q&As about rosemary but none are quite specific enough for newby growers.

I want to transfer a store-bought pot into a bigger container but I need a detailed description of the soil content: top? peat? jiffy? sand? gravel? and any combination and layering that would be successful?

Probably the number one thing about potting soil for rosemary is to make sure that it drains very well. Rosemary definitely does not like "wet feet". Now, to get good drainage you have to consider several factors: the soil itself and the container. The container has to be capable of allowing the water to escape out the bottom. You would be surprised to learn how many newbies fail to appreciate the importance of having holes in the bottom of the pot to allow water to drain. Newbies are tempted to use containers (such as glazed pottery) that have no holes so water does not drip over furniture and floors. Over time the lack of drainage holes will kill plants such as rosemary.

There is no one "right" formula for potting mixes. Rosemary, and most other plants, will tolerate a range of mixes provided that a supply of nutrients is provided and basic physical requirements such as drainage and organic matter are satisfied. Similarly, for many other plant requirements, there are no exact rules for success, only approximations and guidelines. That is why you don’t see a lot of precise directions -- there are always more than one way to achieve success.

For rosemary, you can start with a commercial potting mix and add 10% by volume perlite or sand. If, as most commercial mixes are, the mix is 100% peat-based mix with no compost or top soil, it may not drain quickly and the sand or perlite will improve drainage. Bad drainage is when you water to the pot’s rim and water takes more than 10 seconds for water to come out the bottom of the pot (this is for pots less than 30cm/12"; it takes more time for large pots).

Most commercial peat-based mixes lack much nutrient charge and plants grown in them will need regular feedings. Add liquid fertilizer at half strength every 2-4 weeks during the periods when you see active growth. Do not fertilize if the plant is growing very slowly during the winter months.

When you say don’t over water, let it dry but not dry out, what exactly are you saying – water once a month?

Never water by rules such as "once a day," "once a week, "once a month," or whatever. Water requirements vary considerably depending on many factors which change according to the weather, season and state of the plant. The best rule is: check every day, water only when dry to the touch. If the soil feels even a little moist, it doesn’t need water. When the soil is dry, water thoroughly so that water comes out of the bottom of the pot. If water does not come out, water again until it does. The trick is to not let the soil dry out like a bone – that will kill your plant most assuredly. You will see leaf wilting when that happens and wilting is a sure sign your plants need water immediately.

In the summer you will find that you will have to water more frequently than in the winter. If your pot is big and your plant is small, you will find that you will water less often than a similar plant in a smaller pot. It is an adage in the greenhouse industry that the hardest skill for workers to learn is watering – because watering requires a real sensitivity to the always changing conditions and needs of plants.

My plant I plan to keep indoors in a pot but would it be better if I let it outside in summer?

Light will be much better outdoors in summer. You will find that if you move your rosemary out for the summer, it will grow much better. It is better to keep your plant in a pot and not plant it into the garden. If you have an area with dappled shade or light shade, that would make it easier to bring the plant back indoors in fall because the plant will already be partially accustomed to the lower light levels of indoors. If you are planning to overwinter in a greenhouse, shade while outdoors is not as important.

Back to Growing Herbs | Q & A Index

Copyright © 1997-2014 Otto Richter and Sons Limited. All rights reserved.