It was around this time last year that our new greenhouse arrived. Now that we’ve come a full year’s cycle, I’ve been thinking about what’s worked and what hasn’t. I wanted a greenhouse for two reasons: (i) to safely raise perennial and annual plants from seed (so I can be sure that no chemicals or pesticides have been used); and (ii) to provide an all year round productive space.
For the first half of the year, the greenhouse did a really good job of safely raising seedlings. I managed to grow a good range of perennial plants, including sea beet, Caucasian spinach, good king henry, kale, garlic chives, wild rocket, and lovage.
I grew annuals including tomatoes, salad greens, kale, French marigolds, snapdragons, basil, parsley, and more.
I was determined to use peat-free compost. Finding a good one isn’t easy, but I used Sylvagrow with added John Innes, and it performed well. It isn’t available locally, so I had it delivered from an online supplier. This obviously bumps up the cost quite a bit, so I just used it for seed sowing and raising seedlings. For my salad troughs, which require a lot more compost, I used veggie soil from a local supplier. It is peat free and cheap, but isn’t actually a potting compost.
As the year went on, I started to encounter problems. The first was the number of plastic compost bags which I ended up accruing. I don’t throw them away as I prefer to reuse things rather than ‘landfill’ them (especially plastic). But there is a limit to how many empty compost bags I can actually use. So I need to find a growing medium that doesn’t proliferate plastic bags. The only way that I can think of to do this is by making my own.
The second problem was that a load of compost fly arrived with the veggie soil. Compost fly are not a nuisance for mature plants, but unfortunately their little grubs feast on seedling roots. Once the compost fly arrived, the seedlings stopped growing.
A third problem, which is related to the relatively dark situation of the greenhouse as well as my ineptitude in keeping things too damp, was the arrival of powdery mildew. This particularly liked the chard and kale baby leaves.
For this year, then, my objectives are to learn: (i) how to make my own greenhouse growing medium; (ii) how to manage pests in the greenhouse – specifically compost fly and powdery mildew. The eagle-eyed amongst you will have spotted a problem here. If I’m putting the compost fly and mildew back into the compost (erm – yes, I am), then my home-made compost will not be a pest free growing medium for the greenhouse. I’ve already had a go at making potting medium from home made compost, leaf mould, sand, blood fish and bone, and garden soil. I can see from the arrival of enthusiastic volunteer seedlings that I don’t kill the seeds in my compost. I also found a slug under a pot. That explains the vanishing remains of seedlings that were already struggling.
In summary, the problems that I face if I use my own growing medium include slugs, seeds, compost fly, and powdery mildew.
Things that I intend to try to address these problems are:-
- Turn my compost every month to heat it up and kill the seeds. This is a pity, because I actually delight in ‘volunteers’ in the garden. An alternative is to create the compost and pot it up, let the seedlings grow, and ‘hoe’ them off before sowing the stuff I actually intended to grow.
- Check under pots for slugs regularly. Put down something they might love to hide under, and check that regularly. Put ‘bait’ in there, such as a large cabbage leaf.
- Grow the things that aren’t susceptible to powdery mildew, such as oriental greens.
- Don’t overwater in winter, don’t underwater in summer, and don’t water foliage.
- Clean greenhouse and pots thoroughly to remove mould spores.
- Try biological control for compost fly, including carnivorous plants.
- Try sowing seed into leaf mould (do compost fly lay eggs in leaf mould?)
I’m learning the hard way that a greenhouse is a micro-environment which is more susceptible to pests and diseases, as it is a closed system rather than an open eco-system. There are fewer natural predators, and the air and sun can’t get at the plants freely. Trying to manage without commercial potting compost, and particularly without peat-free compost, makes a difficult task even more tricky. But that is no reason not to try.