Last week we starting this topic off with some basic principles of water and plants, and some tips on watering in your garden. If you stumbled on this blog without seeing that one, check it out first. There we have some valuable background on plants and water, and how to water your outdoor garden more effectively. In this blog we are going to focus on watering plants in containers – outdoor planters and boxes, and also indoor plants.
Getting Started With Outdoor Planters
Growing plants in containers outdoors is always a great way to build a garden in a difficult place, from a balcony to a paved garden. It is also perfect for many urban gardens, as well as for terraces and patios. A garden with planters looks so much richer and full of color and life. But a lot of people have trouble with planters, so before talking about watering them, let’s look at some general points.
- Planters need Drainage Holes – this is a very simple point, but one that many people try to avoid. Every single pot you grow in MUST have a way for the water to escape (we are not talking self-watering containers here). If you have a beautiful container with no drainage, there are two options. One is to use a drill and suitable bit to make at least one large hole in the bottom, or several for a large container. The second way is to use a regular plastic pot inside it and be prepared to lift that pot regularly and empty the container – at least once a week, and ideally after each watering.
- Don’t Put Pots in Saucers – I know, you don’t want your wooden deck to get wet, right? Trouble is, with the exception of a water plant like Papyrus, potted plants don’t like standing in water. So, if you do need to use saucers, empty them after watering, or after rain if they are outdoors. Sorry, no way around that one.
- Don’t Fill the Bottom of Your Pots with Gravel – I know, you do it ‘for drainage’, right? Sometimes you can get away with a plant in a undrained pot by putting rocks and charcoal in the bottom, but it won’t last long. If you do this with regular pots, it has the opposite effect. Due to an interesting and slightly complex piece of physics, gravel underneath finer soil creates a ‘perched water table’ that traps water inside the soil, making it wetter, not better drained. You will have to trust me on this one. . .(or do some Googling)
- Use a Single Stone to Cover Drainage Holes – this is the flip side of the previous point. Just cover that hole with a single flat stone or a broken piece of clay pot. You can also use old screening from a screen door or window to prevent soil from washing out.
- Don’t Use Garden Soil in Planters – it can be tempting, but garden soil won’t drain properly inside a pot. Use a blended soil, and try to find one that matches your purpose – outdoor blends for outdoor pots, cactus blends for succulents, azalea blend for acid-loving plants, etc. Some plants, like roses, can enjoy up to 20% garden soil mixed in, as they like heavier soils, but as a rule, don’t add any. It can also add weed seeds and diseases, so. . .
- Many Commercial Soils Don’t Drain Well – this is a sad fact, and many experienced gardeners add up to 20% coarse perlite to most commercial mixes – better to have to water a bit more often than have your plants sitting constantly in wet soil.
How to Water Planters
Just like in the garden, the first ‘rule’ is to avoid constantly watering. ‘Just in case’ is a bad watering method! Many people over-water, or they water ‘just a little bit’. Both of these are bad habits it can be hard to break. Instead aim to water when your plants need it.
- How do you know that? If you are using a suitable mix, and have good drainage in your pots, simply look at the top of the soil. Is it dry? If it isn’t, don’t water. Simple.
- How ‘dry’ is ‘dry’? That depends on what you are growing. For plants that need plenty of water, that would be about the top ½ inch to 1 inch at the most. For ordinary plants it could be 2 inches. For cactus and succulents, let the soil dry almost completely to the bottom of the pot.
- Water less in winter, and more in spring and summer, where you will see that watering might switch from once or twice a month to once a day.
- Water in the evenings if you can, it leaves the plants all night to take up plenty of water to be ready for the next day’s heat.
Watering Your Houseplants
Getting houseplants right is tricky, because there are many variables. Room temperature, light levels, season, and the specific needs of the plant all need to be considered. After a while you will get to know the rhythm of watering your particular plant, although they will change dramatically as they grow.
- Forget all those ‘water once a week’ ideas, and use the same rules as for outdoor planters. Is the soil dry? That is the only question you need to ask yourself.
- Experienced waterers in greenhouses don’t even look at the soil – they pick up the pot. Does it feel light? Water. Does it feel heavy? Don’t water. Practice this method and your watering will be great – although of course it won’t work so well for big floor plants, or plants in big ceramic outer pots! Great for all your table and windowsill plants, though.
- In winter the temperatures indoors may be just as warm, or even warmer, than in summer, but light levels will be a lot lower. Best to keep your plants dormant through the winter months, and you can do that best by holding back on watering as much as possible. Tough houseplants can go for weeks in completely dry soil, and if the leaves are firm and not drooping or soft, don’t water.
- Save watering for when they are growing, because as we said in the introduction to the first part of this blog, without water plants won’t grow, even if they aren’t dying.
Don’t Forget the Fertilizer
Finally, a ‘secret’ related to watering. Every good grower of planters and indoor plants uses fertilizer. It can be chemical or organic, as you wish, but plants in pots need regular feeding during their growing seasons. Half-strength every second watering is good, or quarter-strength every time you water, with the occasional watering with clean water to keep the salt levels in the soil from rising too high.