Cultivating small growing Cacti on window sills, balconies & patios

Last updated: 21 April 2018


Equipment and Materials: Potting container of prepared substrate - small plastic pots.
Acidifier solution - Liquid fertilizer with micronutrients - pH testing solution with vial.
Garden hose power spray attachment - large sieve for washing pumice to remove dust

Introduction & Overview

Although I enjoy cultivating and displaying all arid land plants, I have a particular fondness for cacti.

Advancing years are beginning to catch up with me and I now have difficulty walking and keeping my balance, so I cultivate small growing species in containers in such a way that they will be easy to maintain and carry. This is of particular importance in following my winter maintenance regime which involves staging my plants indoors on south facing window sills at night, and during cold days, and staging them outdoors for the benefits of sunshine and fresh air during the 60°F or so (approx. 16°C) days that we frequently experience during our Tucson winters. Therefor the cacti that I cultivate here at our retirement Town Home are plants that can be maintained in 2" (5cm) and 2¾" (7cm) square plastic pots.

They are all small growing tropical cacti that can be easily propagated via seeds, or offsets/cuttings and do not requiring a cold winter rest in order to produce flowers. Such cacti are ideal for indoor winter windowsill growing.

Selected species

Pereskia portulacifolia
Habitat: typically interior dry regions of the Dominican Republic and Haiti


Rooted cuttings growing in 2" (5cm) - by 3" (7.5cm) deep square plastic pots


Established plant growing "bonsai style" in 2" (5cm) square plastic pot


Frailea castanea
Habitat: typically interior dry regions of southern Brazil


Seedlings growing in 2"x2" (5cm) square plastic pots



Plants growing in 2¾" (7cm) square plastic pots


Discocactus buenekeri (sensu lato)
Habitat: typically interior dry regions of eastern Brazil


Seedlings growing in 2" (5cm) - by 3" (7.5cm) deep square plastic pots


Juvenile plant just developing a cephalium


Mature plants growing in 2¾" (7cm) square plastic pots


Flowering mature plants growing in 2¾" (7cm) square plastic pots


Discocactus horstii
Habitat: typically interior dry regions of north eastern Brazil

One of the criteria I use in selecting plants for my present collection is that they freely produce offsets, or have reasonably thin stems that provide easily rooted cuttings, thus facilitating vegetative propagation. I believe I was discussing this with K.W. during his last visit when I made the somewhat rash statement that I was getting too old and infirm to grow cacti from seed and that meant I would no longer be cultivating one of my all-time favorite species -- Discocactus horstii -- which is one of the real gems of the Cactus family Well, I couldn't stand that omission, so here is a tray of seedlings I have raised this year:


Discocactus horstii
growing in 2" (5cm) - by 3" (7.5cm) deep square plastic pots

Exemplars from my past cultivation efforts:


Uebelmannia pectinifera
Habitat: typically interior dry regions of north eastern Brazil
Seedling and mature plants in varios stages of growth


Melocactus matanzanus
Habitat: dry coastal regions of north western Cuba


Mature plant with cephalium growing in 2¾" (7cm) square plastic pot


Root system of mature plant with cephalium


Mature "rescue" plants in flower growing in
2¾" (7cm) square plastic pots



Mature plant bearing fruit in cephalium


Multi headed offsets with cephaliums resulting
from apical damage to mother plant


My general approach to Cactus cultivation

Much of my approach is based on that espoused by Dr. Franz Buxbaum in his book CACTUS CULTURE BASED ON BIOLOGY (translated by Vera Higgins), Blandford Press, 1958. He was a pioneer in the use of mineral rich coarse textured growing media to insure superior drainage and root aeration -- acidifying water and soil by testing and modifying the pH -- using complete, balanced fertilizers incorporating micronutrients -- and using non-porous pots in order to maintain healthy root systems.

The information I present here in general reflects that approach. It is important that you follow your own path in cultivating your plants based on your own physical capabilities, the requirements of the plants that you grow, your growing environment, your climate, and the type of containers you use.

Containers

I grow all of my cacti in ubiquitous commercial plastic pots which I believe contributes to producing healthy and robust plants.

In addition to their light weight, a great feature of using plastic pots is the ability to easily slide established plants out of their container (and afterward slide them back in) in order to examine the condition and health of the root ball structure.


Discocactus root ball

Soil Mix

I have always experimented with soil mixes -- I think I have used about every one that has been devised during my growing lifetime -- and I have found all those that were of coarse and gritty texture, thus providing excellent drainage and root aeration, consistently produced healthy and robust plants.

In addition to producing healthy and nice looking plants, ease of plant maintenance is an important attribute of soil mixes in my opinion. They should tolerate occasional watering misadventures and be light enough to make potted plants easily transportable.The latter is of great importance for older growers, or those who are disabled to some extent, and who have difficulty walking and keeping their balance or have diminished strength in their hands and arms.

I mostly use a very porous, well aerated and reasonably light weight soil mix for cultivating these cacti -- 80% washed pumice plus 20% aged and weathered pine bark fines. I incorporate encapsulated slow release fertilizer (Osmocote) in the mix.

I don't screen out the small granular pumice fines - but I do wash out the dust using a fine sieve in conjunction with a "power spray head" garden hose as dust tends to migrate to the bottom of containers where it can form a drainage impeding "sludge".


Washing out dust using a "power spray head" garden hose and fine sieve.


The pumice described above after washing it to remove dust.


Prepared soil mix ready for use in potting plants
80% washed pumice plus 20% aged and weathered pine bark fines.


Melocactus growing in above mix

Some of the plants illustrated here are growing in 70% Bach's Cactus Nursery mix plus 30% raw pumice (+/- ¼"/6.35mm).

Dan Bach's Cactus Nursery mix:
60% screened coarse and uniform (3/8"/9.53mm) horticultural pumice
20% high quality Canadian sphagnum peat moss
20% well composted shredded pine tree forest bark

I cannot perceive any difference in the quality of plants grown in either mix.

I think a high quality commercial bagged potting soil (very low in peat) mixed with a suitable proportion of ceramic (fired clay) material such as "Turface" or plain "Kitty Litter" or coarse perlite, should work pretty well.

Watering and fertilizing

Watering: I use Tucson City tap water exclusively. I check and adjust the pH to ±6.0 using a General Hydroponics GH1514 pH Control Kit.

Fertilizing: I use a commercial 10N.30P.20K fertilizer (with micro-nutrients) at 50% strength (approx. once per week) during the growing season.

Watering Regime

Active growing period (outdoors under 30% shade cloth): With the arrival of warm spring weather I water my plants with increasing frequency. I insure my plants receive copious amounts during the hot Arizona summer months, When I water during this time I do it from above and soak the plants until the water runs freely from the drainage holes. During our Arizona summer "Monsoon" thunderstorm season the frequent (but sporadic) heavy rains (quite acidic in the pH 5.0 to 5.5 range) reduces the hand watering requirements for my container grown plants significantly.

Because these are CAM plants (stomata opening at night) I water at early evening, often every day except for thunderstorm days, during very hot weather here in Tucson, which equates to late May until late September, when the high daytime temperatures are often in the 100°F+ (approx. 38°C+) range (often much higher) with night time temperatures dropping into the 75°F (approx. 24°C) range.

Resting period: These plants do not require a winter cold resting period in order to produce flowers the following spring (that is one reason I favor them). Winter dormancy for them results from the very dry conditions they experience during this time in their habitat. Therefor they only receive occasional light spraying or misting during this time to maintain general plant health. I use a common garden plastic spray bottle (approx. 2 quarts/1.75 liters) filled with regular Tucson tap water. I add sufficient acid solution (or distilled white vinegar) to attain a pH of approx. 6.0. From time to time, and infrequently, I add a little fertilizer in order to provide the plants with some nutrition.

Staging plants

During cold days, and at night during the winter months, I stage my plants in small square plastic pots within trays indoors on south facing window sills that receive full sunshine. On sunny winter days, when the temperature rises to around 60°F (approx. 16°C) -- which happens quite frequently in southern Arizona -- the trays go outdoors being staged, in full sun, on a wrought iron stand just outside my south facing bedroom window. When the temperature drops at nightfall (or sometimes during the day) I slide the window open (the screen has been removed) and retrieve the trays one at a time (they are light weight) by reaching out through the open window and positioning them inside on the windowsill.

With the arrival of spring - when the daytime temperatures climb into the 80's F (mid 20's C) and the nighttime temperatures are in the 50's F (10's C) - the plants are staged outdoors on plant stands under 30% shade cloth until the arrival once again of winter temperatures.


Summer staging under 30% shade cloth


Some small growing Brazilian cacti on plant stand - close-up photo


Link to the Cactus Cultivation Directory