How to keep greenhouse plants healthy

I have loved my greenhouse since the moment it was built, but in the past I've had problems keeping the plants in it healthy. This year is my best year so far, so here are the tips about what I've done differently this year:

1. Grow all your own plants from seed. This way you know you're not accidentally importing any infestation.

2. Keep the greenhouse door and window shut as much as possible until the plants start to flower if you are only growing plants that cope well with heat. I only opened my door to go in and water every day before the plants flowered, and my aubergines, peppers and cantaloupe melons seemed perfectly happy with this level of heat. It's meant that I'm now only dealing with a relatively small greenfly infestation on my aubergines.

3. Keep an eye out for infestations and deal with them as soon as you spot them. My aubergines have had greenfly on them this year. I have dealt with these by crushing as many as I could on the leaves between my fingers and thumb (fingers one side of the leaf and thumb the other) - although watch out, aubergine leaves grow occasional spines, so make sure no spines are about to penetrate your skin when you do this. I also sprayed with a mixture of washing-up liquid diluted in plenty of water, because I didn't want to crush new leaf growth between my fingers and also I didn't think I'd squashed all the greenfly despite my best efforts. The washing-up liquid and water approach is a tricky balance. Too little and it won't kill the greenfly, too much and it will damage the leaves. I've erred on the side of not killing enough greenfly, so I still have greenfly, but my aubergines are all still alive and thriving.

4. If you don't have many flowers and don't want to open the door for bees yet. you can pollinate with a paintbrush. I'm pretty sure the purple pepper in this picture is a result of paintbrush pollination. Just brush the paintbrush over the centre of an open flower on one plant and then on the open flower of another plant of the same kind and back.

5. Make sure you fertilise. I've long been feeding my greenhouse plants with liquid seaweed feed once or twice a week. But this year I realised it probably didn't contain enough nitrogen for them, as the lower leaves have been going yellow, which is a sign of nitrogen deficiency, so I supplemented the liquid seaweed feed with chicken manure pellets placed on the top of the compost in the pots and watered in. This seems to have helped a great deal.

6. Grow chrysanthemums in the greenhouse. I should have started mine earlier, so they're not flowering yet. These are supposedly a deterrent to pests (possibly they simply have an overwhelming smell that pests find unattractive), and the greenhouse seemed to have fewer infestations last year when I grew them.

The rest of the garden is also looking good, although further behind where I'd like it to be. Regular evening patrols to collect slugs and snails seem to have helped a great deal and are allowing the garden to fight back from the devastation these caused earlier in the year: