My tips on growing natives in containers

I want to start this post by stating the obvious: the following tips are things that I do to grow plants in containers. Some of my suggestions are not conventional, in fact, some plant people may strongly disagree with me. The main reason for this is that I do not purchase potting mix, amendments, fertilizers, pesticides, organic soap, horticultural oil… and the list goes on. I use what I have on hand, except for the plants, containers, and water and parts for the temporary drip irrigation system. If a plant gets sick, I make little effort to heal it. If a plant needs supplemental nutrients, I either repot it with additional compost, top-dress it with worm castings (from my worm bin) or throw it out. All in all, I do well with containers, unless we are traveling a lot and they are neglected. Remember, container plants require careful attention more than anything else.

Potting soil/fertilizer
I use a homemade potting mix consisting of oak leaf mold, compost, and garden soil. For plants requiring excellent drainage I add coarse sand or coarse perlite (one of the few amendments I sometimes purchase). Minimize fertilizer to keep the growth rate low, but use a dilute application if plant seems nutrient-deficient (yellowed leaves). Rather than fertilizing most container plants, I repot them since the soil can be deficient in many macro- and micronutrients. However, heavy feeders (like vegetables) may need supplemental fertilizers. I start with a fairly rich soil (high in organics like compost and leaf mold) and top-dress the soil with compost and/or worm castings. Many native plants do best with lower nitrogen levels since excess nitrogen promotes rampant growth that is unsustainable in our hot and dry climate.

Oak leaf mold taken from layer below fallen leaves of coast live oak. So nice!

Mix leaf mold with garden soil, add compost and/or worm castings for heavy feeders (vegetables, eg.), coarse sand or perlite for plants requiring excellent drainage. I don’t put anything in the bottom of the pot.

Water
Water when the soil is dry and the plant appears to need water – slight flagging of stems, or other signs. Check the soil at the surface and a few inches down. You can also lift the pot to see if it feels heavy or light. Sometimes the surface dries out, while the soil below remains wet – the pot will feel heavy in this case. Do not water plants that are dormant. Wait until they resume growth and then water regularly. Water thoroughly until the water drips through the holes. This prevents the accumulation of salts since they are carried out with the water that drains through the pot. It also depletes the soil of nutrients (see above regarding fertilizers). Don’t water too often. For most plants, other than those adapted to continuous moisture, it is best to let soil dry out before watering again.

Containers
One of the most important things to look for in a good container is the number and size of drainage holes. Many commercial containers have inadequate drainage, resulting in plant loss due to root rot. Unglazed pots dry out more quickly than glazed or plastic ones, however, if kept moist the pot surface stays cooler. Dark colored plastic pots can get very hot, scorching roots that are growing near the edge of the container. Plant at least an inch below the top of the pot so that water can penetrate the soil without running off. Repurpose household and other objects – boots, cans, wine barrels, wire baskets, old sinks, etc. – as garden containers. Make sure they hold the soil, don’t overheat, and drain easily. Colorful containers can add year around interest to a garden.

Location
It is best to keep pots up off the ground, unless they are sitting on a thick layer of gravel or sand. The roots of potted plants growing on soil will eventually grow through the hole into the soil below. If this happens, drill holes in side of pot so it doesn’t get water logged. Once a plant’s roots have established in the soil below, it usually stresses the plant greatly to sever its roots, so be prepared to enjoy the permanently-situated container. Plants are also more susceptible to earwigs and other pests if located on the ground. And finally, soil, insects and debris can easily clog the drainage holes of plants sitting on ground leading to root rot. Periodically check the drainage holes to make sure they are clear. Most container plants do best with some shade, especially in the afternoon. It is very important to make sure that the roots don’t cook from a solar-heated pot and soil. Move plants to a sheltered spot when extreme weather is predicted (heat-wave, frost or high winds).

One of several holes drilled through the side of the pot along the bottom to aid drainage since the roots of this plant have grown through the bottom drainage hole into the soil below. The plant is now immovable, but it looks too good to destroy.

See what I mean? It is soooo pretty and just keeps blooming!

Disease
I rarely succeed in controlling pests and disease so I first move the infected plant away from other plants to limit the damage. Aphids usually occur only in spring, disappearing in the heat of summer. Cut and remove young stems infested with aphids and hose off the plant. Pick out or dab mealy bugs with alcohol. I usually dispose of a plant with mealy bugs because I am rarely able to fully remove these nasty bugs. In dudleyas and coral bells, and other plants susceptible to them, the mealy bugs snuggle into tiny, inaccessible spaces. Other common pests include red spider mites scale and thrips. These, along with mealy bugs, often hitch a ride into your the garden from the nursery where you got them, so consider quarantining new plants until you are sure they are pest-free.

Transplant
Just as the only way to know when to water is to watch the plant, your plant will usually give indications when it needs to be repotted. Repot when roots are growing through the drainage holes. If allowed to continue, they may grow into the soil below (if they are on the ground). Furthermore, the roots can plug the drainage holes so water stagnates in the pot, leading to root rot and nearly certain death. If the plant needs water more frequently than usual, and the weather is not to blame, it is likely that the roots are filling the pot and there is little potting mix left to hold water. Repot immediately. Sudden growth spurt and vigor may indicate that the plant’s roots have extended into the soil below the pot. Repot the plant into a larger container before it becomes a permanent, immobile garden character. If this happens – and you are okay with it – be sure to drill holes into the side of the pot near the ground so water can drain from the pot (see picture above).

Should have taken care of this earlier! Still after dividing it up (and getting torn to pieces, even wearing garden gloves), it looks like it will pull through just fine. It is a non-native, can’t-kill-it-for-anything agave.

Here’s one of the rosettes several weeks after transplanting. Its central core is firm and growing. The outer leaves will fall off and it will once again thrive, ready to tear apart with its amazing leaf spines anyone who dares to approach.

Be adventurous
Many plants are easily propagated from cuttings or seed. Monkeyflowers, for example, root readily from cuttings, and bloom when young. They are beautiful container plants that can be transplanted into your garden when they outgrow the pot. Sprinkle seeds or plant bulbs in containers for a beautiful springtime wildflower display. For bulbs, once they have gone dormant move the pot to a protected spot and do not water it again until they start to grow. Some bulbs will perform for years this way. Manzanitas look absolutely fabulous as container plants and I have tried them several times. Unfortunately, they die abruptly as soon as the root tips reach the pot’s edge. Nevertheless, I have seen these plants used to great advantage in containers; so if they appeal to you, give them a try, but consider using pots with well-insulated walls. The list of native plants for containers is just a start; there are many native plants that will do well in containers, some for a short-while, others for many, many years.

Pot full of baby blue eyes. Isn’t it cute?

Final words of caution
Most container plants require careful attention. If you travel a lot, you may want to restrict your containers to succulents or cacti that can survive neglect, especially in the summer.

This slideshow includes many examples of unusual container plant arrangements. Be sure to check out the captions for additional information.