Mildew on Courgettes

Courgettes and the cucurbit family can be susceptible to powdery mildew. My courgettes have all succumbed to it this week (August 2021). Off I went to the library, and I looked to garden literature to compare expert advice to treat it.

Topics below include:

  • What is powdery mildew?
  • Whether it affects the fruit
  • Can it be treated?
  • What to do with the leaves
  • Future prevention

What is Powdery Mildew?

This is a fungal disease that covers the leaves, giving the entire leaf a white dust-like coat.

Sally Smith (2010): she described it on the BBC Dig In Blog (2010) as a disease which favours dry soil, when dry days are succeeded by cold nights (BBC Dig In blog, bbc.co.uk, 2010).

Alan Titchmarsh (2009): he says powdery mildew can appear after a dry summer when the evenings are getting cooler (How to Garden, BBC Books, 2009).

Guy Barter (2018): the chief RHS Horticulturist as at 2018 explains it is part of a group of fungal diseases, mainly separated into either powdery or downy mildew. The powdery one is the white covering which affects courgettes and he says they are not necessarily singular – the infection could be unique to your courgettes, for example (RHS Can Anything Stop Slugs?, Mitchell Beazley, 2018).

Mildew on my courgettes

My Courgettes in August

My own courgette plants, of the varieties of Astia, Romanesco, and De Nice, have all succumbed to mildew this week (August 2021). In July, only one of the plants, a De Nice courgette, gained powdery leaves during a heatwave. Meanwhile the rest (there are about a dozen plants in total) remained unaffected. They were watered daily and received a mulch of grass cuttings.

Fast forward to August and gale-force winds preceded a fortnight of persistent rain. These container plants were moved temporarily. Their new spot was exposed so I moved them close together to support each other in the gales. Watering was every couple of days. With all this rain, I did not think they needed much water, but given the exposure and the wind it is possible they may have dried out. It is also probable that they were too close together, hastening the spread of the mildew.

Does Mildew Affect The Fruit?

In my chosen books, authors mostly say that the fruit is fine; it is the leaves that are affected. Here are some author views:

Alan Titchmarsh (2009): the plants affected continue to produce crops but at a lesser rate (How to Garden, BBC Books, 2009).

Aaron Bertelsen (2020): it only affects the leaves (Grow Fruit and Vegetables in Pots, Phaidon, 2020).

Sally Smith (2010): if it is late August or in September that this happens, throw the plant away, simply because it will be unlikely to regrow another yield (BBC Dig In blog, bbc.co.uk, 2010).

With my own affected plants, I have removed the affected leaves. They all look like they’ve had an extreme haircut. Removing the leaves has revealed a few fruits emerging that had previously gone unseen. I’m going to throw out some of the fruitless plants, then retain the ones that look like they will produce courgettes and see what happens.

Can Powdery Mildew Be Treated?

There are chemical options mentioned to treat powdery mildew, but a common approach is care and future prevention.

Christine Walkden (2011): she suggests you grow a resistant variety or use a fungicide that is okay on edibles (No-Nonsense Vegetable Gardening, Simon Schuster, 2011).

Alan Titchmarsh (2009): feed the plant, water it well, and remove affected leaves by hand (How to Garden, BBC Books, 2009).

Guy Barter (2018): give the plant some care. Remove infected leaves as early as possible, water it and mulch it. He notes the home use of milk or garlic, but claims sodium or potassium bicarbonates are more effective. He gives a recipe for bicarbonate spray (image below). (RHS Can Anything Stop Slugs?, Mitchell Beazley, 2018).

Sally Smith (2010): She also mentions potassium bicarbonate spray, used weekly, as a remedy, as well as plenty of water (BBC Dig In Blog, bbc.co.uk, 2010).

Bicarbonate spray in Guy Barter’s 2018 RHS book

What to Do With Discarded Mildew Courgette Leaves?

Differing opinions. Discard, burn, or compost?

Most say discard the leaves, with no mention of where to put them, excepting these two authors I read who said:

Guy Barter (2018): powdery mildew is spread by spores. Burn the leaves and do not add them to your compost heap (RHS Can Anything Stop Slugs?, Mitchell Beazley, 2018).

Sally Smith (2010): she claimed you can compost them because the fungus will not survive the compost heap (BBC Dig In blog, bbc.co.uk, 2010).

I’ve not put them in my compost. I’d love to know if there have been any experiments to test mildew survival on compost heaps. Anyone know any studies?

Future Prevention

Tips offered in gardening literature to resist future mildew on your courgettes include:

Christine Walkden (2011): choose a disease-resistant variety (No-Nonsense Vegetable Gardening, Simon Schuster, 2011).

Guy Barter (2018): consistent watering, mulching, and disease-resistance varieties (RHS Can Anything Stop Slugs?, Mitchell Beazley, 2018).

James Wong (2015): try a diluted milk and aspirin spray (Grow For Flavour, Mitchell Beazley, 2015).

Mildew-resistant varieties of courgettes include Primula F1 and Dunga F1. Anyone else got a variety they can recommend?

Inconstant Tales #2: The Salad Leaves That The Slugs Wouldn’t Eat

I love to grow leafy edibles. The speedier, the better (please send more supplies of focus and patience). But it’s not just the fact that growing salad leaves is a quick way to gain produce. The carpet of green is calming. The number of varieties is wide-ranging, which is just enticing. I am drawn to growing as many types as I can find – or rather, fit in.

However, those young, juicy leaves can be predated by the slug thugs. Seeing your precious green plants all munched can be disheartening, but I see that as an opportunity. The way I see it, the slugs have thrown down the gauntlet of challenge, and I do like a challenge. Can I grow edible leaves that they do not like?

Growing Salads as Experiments

This August, I am planting a round of new leaves which will be left out as part of this annual experiment. Their outcomes will be noted in future posts.

Today’s topic is the main leafy mix that in the last couple of years has gone untouched by our resident slugs and snails. One salad crop is lightyears ahead of the rest: Salad Leaves Oriental Mix. I started purchasing this mix from Simply Seed a couple of years back for an absolute barg of 99p. According to Simply Seed, this mix consists of:

  • mizuna
  • mibuna
  • green mustard pizzo
  • mustard red zest
  • pak choi canton white
  • tatsoi
Oriental Mix: some of the individual leaves

I’ve grown mizuna and pak choi separately as stand-alone crops, with mizuna indoors and pak choi indoors and outdoors. The latter was predated a little by slugs. I can understand that the spicy leaves may be untouched, as I’ve read that they’re not bowled over by spicy leaves, but this mix still carries those unspicy leaves and that juicy pak choi. Yet the slugs and snails did not touch a leaf. Not a single one. These leaves have been outside periodically in spring and summer this year, plus autumn last year, and not a leaf left the building. I advertised them. I left them in a prime spot where the slugs have helped themselves to beets and courgettes, but not these.

Now, I cannot guarantee that this will be the case for everyone. Maybe the slugs will get desperate. Maybe they overlooked the juicy pak choi while the alternatives were more appealing. Nevertheless, I’m going to plant the rest of these seeds, and let them outdoors again, unabashed and blowing free.

Salad Leaves: Oriental Mix in terracotta pot

If you do choose to grow this mix, here are some growing notes:

Salad Leaves Oriental Mix

(from Simply Seed 2019, 2020, 2021)

Position: they have grown successfully in partial shade in a greenhouse or outdoors (at the time of writing, August)

Autumn results: they lasted indoors here in northern England in an unheated greenhouse until (mild) November – later than my cut-and-come-again lettuce types

Soil type: soil used was sieved (peat-free) homemade compost mixed with topsoil

Water: regular watering needed to remain moist (daily in summer)

In situe or transplant: Withstood transplanting

Harvest: continued to regrow after 2-3 rounds of cutting the adult leaves

I’m looking forward to experimenting with the other leaves, particularly the red varieties, but at the same time there’s some trepidation. Some leaves often remain under tight security because I like them too much to risk sending them out into the big wide world! Full of things that see salad as their top takeaway!

Are you growing any varieties of salad/edible leaves, and if so, how are they doing?

Inconstant Tales #1: This Herb is Not a Hotel

My first homemade trough in my new container vegetable garden was stuffed with as many herbs as I could fit. However, three herb plants missed the trip, due to lack of space (a constant issue here). These were two little corianders and a chive fellow. They look upset at being left out because they’ve all had a minor breakdown. The chives have become a hotel for stray aphids; in fact it is fully booked, no rooms left.

This was unexpected. As herbs in general are often advised as companion plants with vegetables, I thought most insects avoided them due to their pungent leaves. I thought this especially of chives. Not so. According to the RHS, they are liked by greenflies. There were mild-mannered lettuces and cabbages next to the chives – why would greenfly not prefer them? Actually, they picked a single cabbage to sit on too, but the chives were the runaway winner. As I have a no-harm rule for all wildlife in the garden, I quickly looked for a way to get them to move on. Use it as an occasional rest stop, fine. But leave the chives some room, okay?

Chives: this herb is not a hotel!

The aphids may be unhelpful for the chives, but they are a food source for our resident hoverflies and ladybirds. For now, the chives have gone to stay with the borage and squash – the area last hosting hoverflies and green bugs. However, the jury’s out on this solution. If they survive the onslaught of aphids, they need a companion plant, a little herb friend.

Coriander and Fennel

The coriander also needs a herb companion. Alone in the greenhouse, it has not fared well, drying out suddenly in a recent heatwave. Outdoors in the herb trough, it flowered immediately, producing seeds but few leaves. Now, it could be the changeable growing conditions lately, or it could its position next to fennel. I knew that dill and fennel are relatives and should not be grown together, but only recently read that coriander should also be away from its familial fennel.

Herb Trough: mint and fennel

The fennel, meanwhile, is happy as larry, while the neighbouring mints are loving life. All these herbs are together in the same trough because they all favour moist soil and the mint receives shade by the fennel.

#FridayFail: coriander

So it looks like there will be no carrot and coriander soup. Maybe some ‘Orange you glad the parsley’s still there’ soup? Or, given the mint explosion, some carrot soup with a hint of ‘After Eights’?

Are you growing herbs? Do you grow coriander, and have you found a companion plant for it?

Small is Beautiful: Grow These Container Vegetables

Want to grow more than salads but you’ve only got space for pots? Leanne Dempsey introduces some suitable container vegetables and offers tips for finding the right varieties.

A lack of ground space cannot stop anyone from growing vegetables. Whether you are armed with only a balcony, a greenhouse, or a few patio pots, you can grow a variety of edibles. In fact, container gardening offers certain benefits of its own. Pots can be raised off the ground for easier access. They can be moved, should the plant need a change in conditions. They can also be grouped, creating companion planting to protect against pests or direct sunlight. Containment itself not only keeps the plant in but could keep certain diseases out – or at least away from other pots. While herbs and salad leaves are great starting points, there are several other vegetables you can sow in a small space that will add to your homegrown harvest.

In theory, almost any fruit or vegetable could be cultivated in a pot. However, some thrive in pots in a way that others do not, because they have the capacity to remain in a small space. Here are just a few examples of vegetables that grow well in containers, as well as a few tips for finding those varieties that prove that small is beautiful.

5 Crops for Pots

1. Spring Cabbage

Instead of waiting for a cabbage to become the solid, ‘head’ variety that you see in the shops, you can grow cabbages in containers for harvesting the young leaves. Using scissors, carefully remove the leaves without damaging the trunk of the cabbage and offshoots. It will regrow leaves on the same stem, producing repeat harvests of tender leaves. Spring cabbage varieties grow well in pots and provide young juicy leaves. Some cabbage plants can still produce a crop of leaves the following year, so save the plants and test them out as perennials.

Try: Spring Cabbage ‘April’ for a type that has bolt resistance and can be grown in a compact space.

2. Potatoes

This cupboard staple is a treat in a container. It is like digging for treasure when the time comes to lift the plants and the soil beneath reveals golden (depending on the variety) spuds. Garden suppliers sell grow bags, pots, and wooden planters designed for growing potatoes on a patio: these bags and pots average from a quarter to a half metre in height with at least a 40-litre compost capacity. These sizes accommodate around 3 or 4 seed potatoes which grow into multiple potatoes in a single harvest. There are different varieties of potatoes for different times of the year, and the early varieties are often the fastest to reach maturity. Check with the supplier’s instructions before planting, in case the variety needs to be chitted. Beginners will benefit from containers with a flap or door at the bottom.

Try: a first early Red Duke of York or a second early Charlotte.

Golden Beetroot in a 20cm Container

3. Golden Beetroot

This compact beetroot is flavoursome; it is milder and sometimes sweeter than its red relatives, and it does not stain your hands when prepared for cooking. They are like jewels in the soil, producing these sunshine yellow roots. 2 or 3 beetroots can manage in a pot as small as 20cm in diameter. Alternatively, grow this root just for the leaves. The leaves are very tasty when lightly steamed or fried. They are ready before the root and can be grown even closer together for a patio supply of healthy tasty greens.

Try: Golden Beetroot Burpees Golden (for the root and the tasty leaves)

4. Carrots

Carrots like a fine soil that is light, sieved, and free from stones. Containers are just the ticket to manufacture a more refined environment to help them grow. Sow them an inch apart where they are destined to harvest. If possible, leave a gap at the top of your pot where the carrot heads can grow below the pot, then cover the pot with horticultural fleece to protect them from carrot fly. Alternatively, varieties like Flyaway and Resistafly have been bred to withstand these flies.

Try: Carrot Amsterdam Forcing 3 for a faster carrot, or Carrot Chantenay Red Core for baby carrots

Dwarf French Beans In a Container

5. Dwarf French Beans and Peas

Dwarf legumes are opportune for patios and balconies where space is low. A 30 or 40cm tub can house a dozen staked dwarf French bean vines. This smaller size of beans lends itself better to containers than, say, towering runner bean plants. Dwarf varieties of peas include Feltham First and Kelvedon Wonder, each rising to no more than half a metre in height. Admittedly, dwarf peas do not always have as long a cropping season as their taller relatives, but they are quick to start cropping because they reach their adult size quicker.

Try: Dwarf French Bean Compass, or Pea Kelvedon Wonder

3 Tips for Choosing Container Vegetables

Naturally Small Plants

Root vegetables do not take up too much room, hence their utility for small spaces. Carrots, radishes, beetroots, and turnips are suitable in containers. Other fruit and vegetables that are naturally compact include strawberries, cabbage leaves, kale, spinach, chard, chives, mint, parsley, coriander, and oregano.

Plants like potatoes, courgettes, aubergines, patty pans, patio peaches, and blueberries will manage in medium-sized pots. Blueberries need an acidic soil, however. They need extra care to ensure they continue to thrive each year in containers.

Choose Dwarf Varieties

Likewise, look for dwarf cultivars of plants that would normally be larger. Spring onions and round carrots are two such examples. French beans, peas, cucumbers, kale, and chillis all have dwarf ranges.

Five Dwarf varieties to try:

  • Carrot – Rondo
  • Chilli – Apache
  • Kale – Dwarf Green Curled
  • Spring Onion – White Lisbon
Kale -Dwarf Green Curled

Choose Speedy Vegetables

When space is at a premium, all the edible plants need to pull their weight if there is to be a sufficient harvest. A variety of vegetable which takes 6 months to produce one round of food is not as useful as one which offers multiple harvests in that same period, or a plant which takes a month to cultivate, after which another plant can takes its place.

Crops like cabbages, dwarf kale, spinach and chard offer multiple harvests if their leaves are harvested young and the trunks of the plants are left intact. Cut-and-come-again lettuce, mizuna, and rocket also regrow. Look for strawberries that have a longer cropping period, or mix early and late varieties to provide you with berries throughout summer.