Is your plant propagator causing you problems?

Starting off plants and produce from seed in a propagator is one of the most rewarding jobs a gardener can do, but it can be tricky. Get things wrong, and you may find your seeds simply won’t grow.

At Keen Gardener, we get lots of enquiries and questions from customers regarding their propagators. Thankfully, the solution is usually fairly simple.

In this handy troubleshooting guide, we provide answers to some of the most frequently asked questions and queries about propagators.

  1. 1.      Why isn’t my propagator heating up?

The top question we’re asked is related to temperature – and specifically, why the propagator isn’t heating up.

Although sometimes, this may be due to a technical fault or user error (check it’s plugged in properly!) in the vast majority of cases – the propagator is working just fine. You can’t tell by touching the soil, but it’s almost certainly heating up to the right temperature!

Unless you’ve set the soil temperature to 30°C or more (almost certainly too hot for the plants), you won’t be able to tell by feel whether or not your propagator is on.

  1. 2.      Why is my propagator too hot, and how can I reduce the temperature?

Another common query we get is how to reduce the temperature of the propagator. In modern, central heated homes, often, the room temperature never gets low enough to trigger the thermostat – and it still ends up being too warm. Even if your propagator is fitted with a thermostat, it won’t be able to reduce the temperature inside by itself.

Often, this is a problem related to the environment/room where the propagator is located. The simplest solution is to move the propagator to a cooler room. Positioning it by a window, or in an unheated room will usually do the trick. If you’re still struggling, moving the propagator outside into the greenhouse can kelp to keep the temperature down.

  1. 3.      Why aren’t my seeds growing?

There are a number of different reasons why seeds might not be sprouting in your propagator. Usually, they are related to one or more of the following:


Check the temperature. If soil temperatures are too high or too low, seeds simply won’t grow. Check on the back of the seed packet (or search online) for the perfect temperature your seeds need to thrive.


Over and under-watering can also stop your seeds from germinating. As a general rule, soil should be warm and moist, but not wet. Over-watering can also expose seeds, which can prevent them from growing.

If the environment inside the propagator is too humid (see below) it can hamper plant growth.


Seeds need nice, fine, even and lump free soil to grow properly. Big lumps and heavy soil can prevent seeds from sprouting, as can big gaps in the soil. Follow the planting instructions on the seed packet, and ensure that seeds are put to the correct depth, and covered.

Before planting large quantities of seed, it can be useful to do a trial batch, to ensure you get all the variables just right.

  1. 4.      Why is there condensation in my propagator, and is it a problem?

Condensation inside propagators is really common – in fact, it’s often a sign you’ve got the conditions right (warm and moist).  It isn’t usually a problem.


Heavy condensation can cause excess humidity inside the propagator, which can hamper plant growth. Wipe away heavy condensation, monitor your watering and check to ensure your propagator has enough ventilation to prevent it from becoming a bigger issue.

Propagators from Keen Gardener

You’ll find a hand-picked selection of high quality heated and unheated propagators at Keen Gardener. From small windowsill units suitable for a handful of seedlings, to expansive greenhouse systems suitable for numerous trays and larger pots, we’ve got something to suit every requirement.

You’ll also find a range of heat mats, thermostats and soil warming cables – ideal for larger scale propagation.

As with all our products, they’re backed up by our Lowest Price Promise.