Month: January 2023

Welcome back to the indoor garden guide. Today’s subject is going to be the various pots/container options you have for growing indoors and some basic guidelines regarding their use.

Indoor plants are usually grown in one of two types of pots: ceramic/terracotta pots or plastic pots. Each has their own advantages and disadvantages but either can be made to work for just about any plant. Before we talk about the actual pots though, we need to have a quick note on the importance of drainage.

As discussed in the last post about potting media, one of the most important things to think about with houseplants is getting the drainage right. Too little drainage will end up rotting almost any plant, and too much drainage (although less common of an issue) will result in plants that constantly need water because they dry out very fast. With this in mind, it is important to always choose to grow the plant in a pot with drainage holes.

Image

Drainage holes are the little holes on the underside of the pot which allow excess water to drain out of the pot. As mentioned earlier, this flow of water is important to prevent the roots from soaking and then rotting in a puddle at the bottom of the pot.

You will sometimes see pots sold without drainage holes for one of two reasons. Reason number one is that they were simply not designed with the health of the plant in mind, they were just designed to either look good or be cheap to produce. This is usually the case with those little succulent arrangements you often see at big box stores:

Image

These collections are actually a bit of a pet peeve of mine because they set people up for failure, particularly with succulents which are extremely dependent on good drainage, which leads to people killing their plants and thinking that they don’t have a green thumb when in reality even an experienced grower would struggle with the same set up. (And they’re usually way overpriced)

The other reason you might find a pot without a drainage hole is that it is intended to be a decorative cachepot, which is a pot you use to look good and contain any mess from a houseplant, but the plant is actually planted inside a different pot (usually a plastic nursery pot with drainage holes) and then the whole thing set inside the cache pot.

Image

This is a totally viable option and a great way to have a good looking potted plant that doesn’t make a mess on your floor/windowsill. The only issue is when people mistake one of these decorative cachepot as a grow pot (what the plant should actually be in) and plant directly into the cachepot.

A common misconception is that you can use a pot without drainage holes if you put a layer of gravel at the bottom below the soil. The idea is that the water can drain out of the soil and sit below the plant roots in the gravel, eliminating the need for an actual drainage hole. However, this is actually not the case due to a phenomenon called the perching effect. The science behind it is explained in more detail in the link, but the general idea is that water doesn’t like to flow between layers of soil with different particle sizes (like potting soil to gravel) and therefore  the gravel in the pot actually raises the water table in the pot and doesn’t help with drainage at all.

Terracotta/Ceramic Pots

Terracotta pots and ceramic pots are both made out of clay that has been shaped into a pot and then hardened in a kiln. The difference is that ceramic pots are usually painted/glazed while a plain terracotta pot is just the raw clay.

Image

The only difference this brings in regard to their use is that terracotta itself is porous, which means a plain terracotta pot will dry out faster than a glazed ceramic pot (even with the same drainage holes). This can be advantageous if you have a tendency to be a little heavy handed with the watering can, or are growing plants that like to dry out fast (like cacti and succulents). At the same time however, it can also be annoying if you live in an already dry climate and the extra evaporation makes you need to water more often.

Pros of Terracotta/Ceramic Pots:

• • • • Often visually appealing and come in a wide range of colors, shapes and sizes
      • Extra evaporation from terracotta (can be pro or con)
      • With proper care can last a very long time
      • Widely available

Cons of Terracotta/Ceramic Pots:

• • • • Heavier than plastic
        • This isn’t a big deal for a small plant on the windowsill, but for a large pot (think 20+ inches across) it can make it hard to move
      • Can break/shatter
      • Hard to drill drainage holes
        • Can be done with special drill bits
      • Usually more expensive
      • Harder to take plants out to repot

Plastic Pots

Plastic pots can also come in a wide range of shapes and sizes, but the most common are either decorative plastic pots (top) or the standard black/green nursery pots (bottom)

Images (Top) (Bottom)

Pros of Plastic Pots:

• • • • Lightweight
      • Cheap
      • Flexible/Doesn’t shatter
      • Huge range of colors/shapes
      • Easy to take plant out to repot

Cons of Plastic Pots:

• • • • Will eventually become brittle over time
      • Some people don’t like the look
      • Some are extremely flimsy

Pot Sizes/Up-Potting

As plants grow aboveground, their roots grow below ground as well. At some point, your plants will need to be moved to bigger pots because a plant left in a pot too small will eventually become rootbound like this:

Image

This will lead to problems in the long run, including issues with drainage and soil compaction. To avoid this, plants must occasionally be moved into bigger pots.

When to Up-Pot?

Signs that a plant is in need of a repotting include numerous roots coming out of the drainage holes and large amounts of roots visible on the surface. Slow water infiltration can also be a sign but isn’t always caused by this. To check, remove the plant from the pot (either by squeezing and pulling on a plastic pot, or by running a butterknife or some other object around the inside edge of a ceramic pot) and look to see if the roots are visible/circling the pot. If the roots have begun to circle, it is likely a good time to repot that plant. Simply remove the plant from its old pot and place it in a new pot that is about 2-4″ larger across than the previous pot*. Then backfill with soil, making sure to bury the plant no deeper than it was in the old pot. If the roots are super tightly wrapped in the old pot, you can loosen them a bit with your fingers or make a couple small cuts in them with a knife to encourage new growth once they’re in the new pot.

*You may be tempted to just put a plant directly in a much larger pot to prevent the need to repot again in the near future, however this is a bad idea. A plant in a pot that is too big will not be able to absorb all the water contained in the excess soil after a watering, and thus will be prone to root rot. Only increase pot size by about 2″ or a little more each time.

That’s all for this post. The next post will talk about plants that can thrive in places with less than optimal lighting (Like a dorm room…).

Welcome back to the spring edition of this blog series. In the fall we covered outdoor gardening, mostly focusing on edible crops. This semester will still be plant related, but with a more specific focus on indoor plants (aka houseplants).

Image 1

Just like in the outdoor garden, the first steps to successful houseplants come with the soil you use. However, the soil used for potting houseplants is not the same as the soil you’d find outside (And its usually referred to as “potting media” rather that “soil”). Even a houseplant grown in the very best outdoor soil would struggle to survive. This is because outdoors the wind, sun, and exposure to the elements makes soil dry out faster than it would indoors. Since plants don’t usually like to sit in soil that stays soaking wet, we need to make up for the lack of these environmental factors by adding materials to the potting media in order to allow it to drain water better and dry out faster.

Materials:

Image 2

We break potting media materials into two categories:

Base media: Materials used to create the base of the potting media. They usually contain mostly organic material, and have a high water holding capacity. Two of the most common are peat moss and coco coir, and commercial potting mixes often have a combination of the two. They are functionally very similar, so it doesn’t particularly matter which one you use.

Drainage/Porosity: Sometimes also called mineral components, these are used to improve drainage by creating gaps through which water can move and also allows air to move through the potting mix

• • • Perlite: Perlite is a naturally occurring siliceous rock that, when heated, expands from four to 20 times its original volume. These are the little white pieces you find in potting mix which resemble Styrofoam. It is extremely light and porous, and when pressed will crush down into a powder. It is the most common additive for improving drainage because it is extremely cheap and works quite well. The one downside is that it can float up to the top of the pot overtime because it floats in water.
    • Pumice: Another naturally occurring rock with tons of tiny holes that is also very lightweight and porous (Although not quite as light as perlite), it is used straight as it is mined, not heated like perlite. This is a better alternative for perlite in most cases, because it has all the benefits and will not float to the top of a potting mix even when watered frequently. However, it is more expensive than perlite and usually a little harder to find.
    • Orchid bark: This name is misleading, as the bark sold as “orchid bark” is intended to be used for orchids, but it is not from orchids. It is usually pieces of fir bark/coconut husk pieces. It makes a good additive for many tropical plants which come from soils that may have a large amount of decomposing plant material mixed in. It is not quite as porous as the above two, and holds a little water.
    • Vermiculite: another naturally occurring mineral which is expanded through heating. It appears similar to perlite, and acts much the same way except unlike perlite it absorbs water so it cannot be used as the primary drainage material for most mixes because the mix would stay too wet.

Can’t I just use a commercial bagged potting soil?

Image 3

The answer to this is a little tricky. For some plants, a commercial mix may be good enough, but not ideal. For others, using a cheap commercial mix will almost certainly result in the eventual death of the plant. Most commercial mixes contain some perlite or other drainage material, but usually they don’t have enough of it. For this reason, it is always a good idea to use a commercial mix more like a base and add drainage material as needed.

*The exception to this would be high end specialty mixes or those made by local nurseries/greenhouses because these mixes may already be mixed correctly. But if you’re working with a bag of miracle grow (or similar) from a big box store, the above advice is important.

Recipes for soil success

The right ratios of base material and drainage for your plants will depend on the species of plants being grown, and it is always a good idea to look up a specific plant before making a soil mix for it, but here are some general guidelines:

Catci/Succulents:

• • • • 20-40% organic material/base mix
      • 60-80% coarse mineral/drainage (No orchid bark)

Aroids (Like monstera, philodendron, pothos, etc.):

• • • • 40-60% organic material/base mix
      • 20-40% perlite
      • 20-40% orchid bark

Ferns:

• • • • 50-70% organic material/base mix
      • 30-50% coarse mineral/drainage

Most Others:

• • • • ~50% organic material/base mix
      • ~50% coarse mineral/drainage

That’s about it for potting mixes, or at least to depth that we’ll be covering in this blog. As always, these are general guidelines and I suggest doing a little bit of your own research before making a specific potting mix.