Reach for the fertilizer

By Jennie Hagen January 18, 2011 03:31 pm
Now is when we begin fertilizing indoor plants with half-strength liquid fertilizers to get them ready for full spring growth.

If your indoor plants have been allowed to spend the past two months without fertilizer (as they should have been), giving them full strength liquid fertilizer now will do more harm than good. It could lead to browned tips and even stunted growth.

It is highly recommended that first doses of fertilizer at the beginning of the growing season be just half-strength for the first two applications, approximately two weeks apart, thereby giving the plants time to adjust and prepare for spring. That will take us up to the middle of February when new growth can be projected in earnest and day length will encourage new life, as well.

Indoor cacti and succulent collections can also have this timetable applied to them with the exception that their first two doses of cacti fertilizer be one-quarter strength, not half.

By way of a quick review, let’s recall what the numbers on labels mean.

First, the order of fertilizers is always the same, Nitrogen, Phosphorus and Potassium, or NPK (the Latin name for potassium is kalemia, hence the “K’’). All label strengths have the same order for numbers, NPK. These three numbers represent the percentage of the particular element that is in the fertilizer, their percentage of 100. For instance, the liquid fertilizer I use for my cacti and succulent collection is 2-7-7, so there is 2 percent nitrogen, 7 percent phosphorus, and 7 percent potassium. This makes sense when you consider what you would like your cacti to do — some growth, flowering and good root system. If I applied a higher rate of nitrogen to my cacti, they would probably burn out trying to speed-grow and might eventually die. They are not designed to grow like grassy lawns, so their “N’’ number is statistically lower.

Indoor orchids are just about the opposite when it comes to label numbers. A good orchid fertilizer will be 30-10-10. Giving the orchids a super-rich concentration of nitrogen is what they love. If you consider their native habitats, they grow off the bark of other plants and get their nitrogen from the rich outer layer of barks and stems, so they need a higher number to get really growing. They also like a rest during the darker days of winter here, even though most are native to more equatorial climates. They do respond to light and dark cycles as well. They also, in their native habitats, have periods of rest. First fertilizing of them should also be one-half strength.

So of course this takes us to our last plant food — for indoor green plants. Most common indoor mixes are 10-15-10, the higher number for phosphorus is what gives your indoor plants the boost they need to bloom.

For those of you who enjoy growing African violets, the African Violet Society of America recommends using normal African violet fertilizer, a 20-20-20 mix, but then use it at half strength.

More information on indoor gardening can be found at www.gardenguides.com and www.extension.oregonstate.edu/gardening. The first web site listed is not associated with this column. The second website has more information that may have local interest.

Until next time, enjoy planning that garden, and don’t forget to play in the dirt.


Jennie Lu Hagen is a La Grande gardener.