How to Fertilize Cycads, Part 1

Cycads have become increasingly popular garden plants in recent years. In addition to the more common Sago Palm (Cycas revoluta), rarer species of Cycas, and cycads like Encephalartos and Dioon are finding their way into upscale landscapes.  Cycads’ increased popularity is due to several factors, including their distinctive look, their drought-tolerance, the intrigue of owning a “living fossil”, and that when given proper care, cycads are stunning landscape features. This article addresses the last factor, proper care, specifically how fertilizing can promote healthy and attractive cycad growth.

To be attractive landscape features, cycads need fertilizer to achieve their best healthy growth. Fertilizing means amending your soil by adding nutrients, necessary elements not sufficiently present in your soil.

The Western Fertilizer Handbook shows 16 Essential Elements for healthy plants in this chart: 

        

·  H – Hydrogen ·  B – Boron ·  C – Carbon ·  N – Nitrogen ·  O – Oxygen ·  Mg – Magnesium ·  P – Phosphorus ·  S – Sulphur

·  Cl – Chlorine ·  K – Potassium ·  Ca – Calcium ·  Mn – Manganese ·  F – Iron ·  Cu – Copper ·  Zn – Zinc ·  Mo - Molybdenum

Plants generally obtain sufficient hydrogen, oxygen, and carbon (as carbon dioxide) from air,  water and sunlight. The remaining necessary plant nutrients come from the soil. Primary nutrients plants need are nitrogen, phosphorous, and potassium. Smaller amounts of calcium, magnesium, iron, and sulfur are also necessary. Finally, even smaller amounts of such micronutrients as copper, manganese, zinc, boron and molybdenum can be important. If your soil and water does not have the above elements in sufficient quantity, you need to add them, amending your plant’s “diet”.

During the past 15 years, we have evaluated numerous fertilizers in our nursery and in clients’ gardens to find the best way to augment healthy cycad growth. Through trial, error, reading, and seeing good results and bad ones, we’ve discovered there are several ways to amend soil to grow healthy cycads.

Before discussing a solution, which I will address in the second part of this article, it may be helpful to address the challenges growers face which led us to come up with some specific ways to improve cycad growth:

1. Alkaline soil, found throughout the country, presents plant growing challenges
2. Alkaline water distributed by major utilities in the USA creates additional challenges
3. Cycads have special nutritional needs different from those of other plants

Alkaline Soil and Waters

The pH scale measures acidity and alkalinity. It ranges from 1 (highly acidic) to 14 (highly alkaline), with 7 being neutral. An increase or decrease of one point equals a multiple of 10, so an 8 pH is ten times the alkalinity of a 7 pH. Rain water pH is slightly acidic, generally ranging from 5.5-6.0. Most garden plants prefer a pH of 5.5 to 7.

Arid regions tend to have soil higher in alkalinity and salts, and lower in iron and organic material.  This is a problem for many ornamental plants. Highly organic content generally results in a healthy living soil that can grow strong, pest-resistant plants. Highly organic soil usually results in soil with a slightly acidic-to-neutral pH. Arid climate soils, without organic or other amendments, typically range from 7.5-8.5 pH.

Alkaline tap water is predominant throughout the USA. Many water utilities add elements to increase water alkalinity because this reduces water’s corrosiveness, heavy metal leaching, “red” water and nitrification. For example, tap water in Los Angeles ranges from 8.0 to 8.5 pH, according to the LA Department of Water and Power.

As you’ll see in the graph below from the Western Fertilizer Handbook, nitrification, the conversion of Nitrogen in soil into a form that feeds a plant, is best at 5.0-7.0 pH.

Following this graph, to use fertilizer effectively (and economically), you want to grow plants in soil from 5 to 7 pH.  If you’re not acidifying or neutralizing your water, and your soil remains as is, alkaline water and soils can prevent Nitrogen from being processed by your soil for your plant’s use.

This Western Fertilizer Handbook graph shows what pH does to nutrients’ availability:

A high pH (alkalinity) reduces key nutrients’ availability, and delays or reduces soil nitrification. Plus, water utilities’ reduction of tap water’s iron and nitrates, beneficial for other reasons, means fewer necessary plant nutrients.

Note that iron (Fe) is less available in alkaline soils (above 8.0 pH). And though color is not always a good indicator of a soil’s fertility, African cycad habitat photos show dark orange/reddish-brown soil, indicating high iron.  Cycads love iron, and arid climate soils and municipal water tend to be iron deficient. When cycads grow well in places like Hawaii, it’s not only that they’re in the tropics, but also that volcanic soil is iron rich.  Look at the “Red Dirt” they’re growing in! Growers in Hawaii and South Africa often scoop ground soil and use it in potting mix (see photos below).

One way to offset deficient organic material deficiency in alkaline soils is to use organic mulch, and organic elements in your fertilizer for all plants, not just cycads.  This helps neutralize soil pH, and feeds your soil, so the soil can feed your plants naturally. Organic mulch also moderates soil temperatures, lowers water loss from the soil, and encourages beneficial microorganisms that help plants grow.

Our next posting will conclude this article by discussing cycads' specific nutritional needs and how fertilizer can address these needs and deal with alkaline soils and waters.