Could Your Ferns Look Better?

Serge Zimberoff is a successful wholesale grower of ferns from Northern California. This is taken directly from Serge’s notes from the April 1996 San Diego Fern Society meeting. Serge covered the following six topics:

• Potting mix
• Water
• Feed
• Light
• Temperature
• Pests

Potting mix should be very low in salts. Manures and compost should be avoided when fresh and used if aged only if well leached by rain water. The mix must drain very well. It does not need lime or superphosphate for ferns, but should have dolomite lime for calcium and magnesium and may include a small amount of potassium nitrate if you wish (see below under feeding). pH is a consideration only if you have alkaline water (pH above 7.0). If so, you could have problems if the pH of the mix climbs above 6.5 to 7.0.

Water has two aspects...what kind and how much. What kind only matters if you are on a well. If so, then you need to have the water analyzed and compare those results to standards set for irrigating plants. Tap or rain water differ only in trace chemicals good for the plants. If you use rai water, you need to consider trace elements (see below under feeding). How much is a different issue! All plants take up oxygen through their roots. Ferns are no exception, plus the added fact that most are epiphytes, which means they are even more sensitive to having their roots wet or submerged. Most ferns want periods of drying between watering, with he notable exceptions of tree ferns and Woodwardia. Pellaeas, maidenhair ferns, and holly ferns will tolerate moisture better than others. Staghorns, footed ferns, and birds nest ferns all should have periods of almost complete dryness between waterings. Overwatering is often indicated by deformed leaves, particularly in birds nest ferns and Nephrolepis.

Feed is more easily overdone than underdone. Only feed when the fern is in a growth mode and then only to keep the fern’s color nicely green. Dark, dark green fronds to an almost blue-black usually is not the normal color and is an indicator of too much fertilizer. Lime-colored new growth that doesn’t darken up implies a need of feed. Use a good quality water soluble fertilizer at no more than 150 ppm (parts per million). It tells how to do this on the package. Do not use slow release fertilizers. Between water soluble fertilizer and tap water and your potting mix, you should have plenty of trace elements available. If you use rain water, you might have some deficiencies, but not often! The elements that you need to make sure are available are nitrogen, phosphorous, potassium, calcium, and magnesium. Most other elements are needed in very low quantities and are present somewhere.

Light is usually obvious. Too bright will burn, whereas bright will yellow the fronds (and look hungry!) and too dark will cause stretching although, if the plant looks sad, it is easy to try lowering the light first to see if that is the problem.

Temperature can be too cold, but rarely too warm unless in a small enclosed greenhouse. Over 95F can lead to trouble and over 105F is dangerous to the quality of your plants.

Pests are rarely problems with plants that are watched carefully. You must examine your ferns often to detect pests early so that they are easy to eliminate. Use a prudent mix of common sense in eradicating pests. Chemicals can be very dangerous and should be used only with care after reading all the instructions on the box or bottle. Some pests of ferns are:

• Aphids -- wash off the first few. If they don’t come right back, that is the treatment to continue using.*
• Mealy bug and scale -- use Q-Tips with alcohol*
• Snails and slugs -- catch and squish early AM or evening. If necessary, use methaldahyde granules as bait where children and pets can’t get at it.
• Watch for less dangerous chemicals in the stores, such as insect hormone analogs that will stop the development of the insects, or use synthetic pyrethroids. New chemicals are coming out all the time that are safer to use. Only use chemicals that have the word ’Caution’ on the label. Try not to use those that say ’Warning,’ and never (ever!) use any that say ’Danger’ or ’Poison.’