Monday, January 27, 2014

8 Tips for Growing Indoor Herbs in the Winter

One of my two perennial lavender plants that I have been keeping indoors during the cold and dark days of winter.  My permaculture herb spiral can be seen outside the window in the background, which I use to grow herbs outdoors during the growing season.  

 Last Saturday, I attended a half-hour class on growing herbs indoors during the winter.  It was being offered for free at one of my favorite local garden centers, so the price was right.  Also, since my experience with keeping herbs alive that I brought inside for the winter has been less than stellar so far (sadly, I’ve had a number of botanical fatalities so far…), I thought that I could learn a thing or two (which I definitely did!).

Since I’m sure that I’m not alone in my herb-growing endeavors, I thought that I’d share with you what I learned from both the mini-class and the handout that they provided to the participants.  This information may be pretty basic for many of you, but many new gardeners like myself are starting from square one, and we need all of the help we can get.  I hope this information is helpful to many of you seeking to maintain some culinary and medicinal herbs indoors during the wintertime. 

8 Tips for Growing Indoor Herbs in the Winter

1.  The most forgiving herbs to grow indoors.   Just about any herb variety can be grown indoors if its basic growing requirements are met.  However, parsley, chives, mint, thyme and oregano tend to be the most forgiving varieties when it comes to inadequate or inconsistent watering and lighting, and also tend to be more disease-resistant.

2.  Light.  In general, herb plants need to have about 6-8 hours of sunlight to grow (the more, the better).  During the wintertime in many regions, there is simply an inadequate supply of direct sunlight during the day.  If this is the case where you live, a grow light (which provides the full-spectrum of light for growing plants) may be necessary to help supplement your light source.  Fluorescent lights can also be used, but grow lights provide the best light for your plants.

3.  Water and humidity.  Since most varieties of herbs originate from the Mediterranean, they tend to do best in somewhat drier conditions.   The basic rule of thumb for indoor herbs is to water less often, but more thoroughly.  Let the soil be dry to the touch between the times that you water, and when you do water your plants, water until it runs out of the bottom of the pot.  Don’t let your herbs sit in water for more than a couple of hours (you can put pebbles in the bottom of the pot to assist with drainage), which can cause root rot problems. 
  • The higher the temp and the lower the humidity in your home, the faster your soil will dry out.  
  • As is typically the case for watering plants, water the soil, not the leaves.  Watering the foliage can lead to fungal conditions.
  • Plants in smaller and terra cotta pots will tend to dry out more quickly.

4.  Fertilizing.  The recommended fertilizer for herbs is a balanced fertilizer, with equal parts nitrogen (N), phosphorous (P), and potassium (K).  This will typically show up on the label as something like “10-10-10,” with the ratios being N-P-K.  Nitrogen is important for leaf growth, phosphorous is important for the growth of buds and blooms, and potassium is important for the growth of roots and stems.  A fertilizer that enhances the growth of blooms is not recommended, since for most herbs (although there are certainly exceptions to this rule such as calendula), the medicinal and culinary portion is in the leaves.

Generally, herb plants only need to be fertilized about once per month when they are actively growing.  Since many herbs can be dormant during the winter, you likely won’t need to fertilize them much during this time unless you see evidence of active growth.  

The mini clippers that I purchased for herb harvesting.
5.  Harvesting.  To harvest your herbs, what works best is to use a small pair of pruners, called “clippers,” or “snips.”  These tools will help you to cut and harvest the delicate herb stems and leaves.  Do not yank on the leaves or pull stems off.  This can create injuries to your plants and provide entrance points for pathogens and infections.

The more you harvest, the bushier your herb plant’s foliage will become.  Also make sure to nip the flowers off of your herb plants.  By cutting the flowers of the plants off, the plant will put its energy into growing foliage and not into reproducing (flowers are a reproductive part of the plant).

6.  Pests.  There are a number of pests and diseases that can affect your indoor herb plants, especially for those plants brought in from the outdoors.  Common pest and disease problems for inside herb plants include aphids, fungus gnats, and white flies. 

Inspect your plants regularly, and never use chemical pesticides if you will be eating your herbs or using them medicinally.  Insecticidal soap work well if you spray it on all of the leaves, but be sure to wash off any plant material that you harvest, as there will likely be soapy residue remaining on the plant. 
Other pest tips:
  • For fungus mites, let the plants dry out.    Problems with fungus mites should decrease as the favorable conditions for fungal growth decrease.
  • Sticky traps are also good for dealing with fungus gnats and white flies.
  • You can also try dipping the foliage of the affected plant into a bucket or large bowl of tepid soapy water.  Gently spraying the foliage with some weak soapy water using a water bottle should also work. 

7.  Transferring your herb plants indoors and outdoors.  
When transferring outdoor plants indoors:  Place them in a shady outdoor location for two to three weeks before you bring them indoors, or the leaves may drop off due to a lack of energy needed to maintain their thick outdoor leaves.  Once you have brought them indoors, try to give them as much sunlight as possible.

When transferring indoor plants outdoors:  Just like us, plants can get a sunburn if not given a chance to develop their thicker and stronger warm season leaves before being placed in the outdoor sunlight.  To avoid scorching your plants when transitioning them to the outdoors, first place them in outdoor shade for a couple of weeks, and then to full sun.  This gives them an opportunity to develop tougher leaves to withstand the more direct outdoor sunlight of the spring and summer.

8.  Tips for Mixed herb Containers
If you want to grow more than one variety of herb plant within the same pot there are a few things to keep in mind:
  • Determine the growing needs of each of your herb plants, including how large each plant will be when it grows to maturity.  Your plants will need room to breathe and grow.  For a 12” diameter pot, there should be no more than five plants, and in the case of some larger plants, even this may be too crowded for the space available.
  • Mounding or trailing plants like thyme, oregano, and peppermint should be near the edges or toward the front of the pot. 
  • Tall plants like rosemary and columnar basil should be planted toward the back or in the middle of the pot.
  • Mid-range plants like sage, chives, and parsley should be arranged in order of shortest to tallest from the edge of the pot.

Bonus info:  I also learned during the class that the essential oils of herb plants growing indoors during the winter will likely not be as potent as those grown outside in the sun during the warm time of the year.  The warmer temperatures and the increased access to sunlight during the growing season encourage the plants to produce more of these phytochemicals, but these conditions are generally absent during indoor winter conditions.   Don’t be surprised if the herbs that you are growing indoors during the winter have a milder scent or flavor than you are used to.

If the leaves on your plants have a burned look, they may have gotten too cold and have gotten a little frostbitten.  This can happen if you have your plants sitting on the windowsill of a drafty window.  Moving the affected plant(s) back from the window about 6-8 inches should make your chilly plants happier.

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