Diatomaceous Earth (DE) - Organic Insect Control

Diatomaceous earth (DE) is a non-chemical pest control agent which uses a 'mechanical' action to which no resistance can ever be developed by the pests it works on.  DE is a fine powder, derived from the sediment of ancient freshwater lakes which contain the remains of simple organisms known as diatoms, which have a silica based 'skeleton'.  It is these fossilised, skeletal remains that provide the pest control as these microscopic shards of silca are deadly to the pest, but completely harmless to humans.  To the insect or mite, it is akin to crawling across a surface covered with broken glass, the shards pierce or damage the skin of the insect, even those with hardened carapaces as they all have weak spots at the joints etc.  Once pierced or otherwise damaged, the 'victim' dehydrates quickly, assisted by the absorbant nature of the earth, and dies. 

Red Spider Controlled by DE on Alocasia leaf

It is effective against insects, arachnids and acarids (mites), including their larva (but importantly not their eggs, so repeat applications will be needed to control a population that has already started the breeding cycle).  It is not harmful to earthworms as it only works when dry. It should not affect larger winged insects (Bees etc) as they would have to fly through clouds of it to have any adverse effect. It works at any temperature, unlike organic biological controls, and can be applied before any pests are spotted so as to reduce the chances of damage occuring before you spot the pests.

It is probably the only reliable method of controlling the 2-spotted mite (aka Red Spider Mite), but works on almost every single garden or glasshouse pest. Other pests that can be controlled are aphids, thrips, whitefly (adults), mealy bug, Lily beetle, earwigs, all other mites, cockroaches, sciarid fly (and larvae) and many others. 


For horticulture, there seem to be 3 methods to apply your DE.

1. Puffer bottle or dispenser to literally puff a fine layer of DE on to the target area - which should be dry as this will only work when dry - try to avoid large clumps or thick layers on plants as this is wasteful and can slow down photosynthesis (which would weaken the plant)
2. Make up or soft paint brush, which can be dipped in the DE and then brush it or flick it on to the target area - this method is wonderful where aphids are clustering on stems as it allows you to target the groups of pests whilst keeping the DE away from beneficial insects.
3. Dissolve 15 grams of DE in one litre of water (add the DE to water and shake well).  Spray on the affected plants so as to wet them, but not so that it runs off.  Allow to dry and it will give a very thin but even coat.

Whichever application method you use, bear in mind that it only works when dry - so if you wash it off when watering or the rain removes it, you will need to re-apply it.  If you can see the DE on the plant, then it is still working, if you cannot see it, then you will need to re-apply.

Once you have killed off the pests (can take 2 or 3 applications to catch all generations and prevent re-population), you can then discontinue its use until you notice pests again.  
Because the DE is food grade there is no minimum interval between application and harvest.  Just wash fruit and veg as you normally would.

If you apply a lot of DE or have any respiratory issues then you should wear a face mask when using it dry. 

There are hundreds of uses for DE, here we are just describing methods to control pest in horticulture.  A rule of thumb application rate for control would be around 2 - 4 grams per square metre of leaf surface being covered at each application - this amount will remain effective until it is removed by rain or watering.

Why Not To Give Up On Seeds You've Sown

Weather has picked up, the greenhouse is getting warm during the day, so thought it was time to start repotting last years seedlings.  We started mist spraying the pots around the end of January to get the roots going on the succulents, which includes several pots of Agave seedlings.

Today as I potted up some Agave americana, here's what I found...

 New seedling to left of year old Agave americana

The new seedling, still with the seed case on the tip of the seed leaf, had germinated almost a year after the original sowing back in Spring 2018.  2 more were found in this state.  It just shows you should never give up on seeds in a pot, especially in the case of succulent plants where not all will germinate at the same time as a defence against poor growing conditions during any one season which would otherwise spoil the whole crop.

Amorphophallus Corms

 Amorphophallus

Most years we have Amorphophallus bulbifer tubers in stock, usually during the period January to July (after that we have either sold out for the year or planted them ourselves to save any extras going to waste).

Every now and then we get other species such as konjac and nepalense in stock or as offshoots of our own plants - rare events so the availabilty is patchy.

To plant these corms and tubers, you will need a relatively wide pot, at least 4 times wider than the corm.  If potting several corms, allow sufficient space for the corm to double in size, in this way they can stay in the same pot for a couple of seasons.

To plant them, there is a 'right' way up and a 'wrong' way.  The right way is with the domed side uppermost.  If there is no obvious domed side, not to worry as planting the wrong way, the corm will still send a shoot up and its roots down and sideways.   Plant each corm to at least its own depth in compost.  Free draining compost is ideal, either soil or peat based.  If using peat based, add some perlite or vermiculite so that it is easily re-wet after the winter rest.

Warm, bright but out of direct sunlight until the leaves are full developed - so under the shade of shrubs or on the greenhouse floor.

The plant will tell you when it needs water (it will have a shoot above ground) and when to stop watering for the year (the shoot withers and yellows).  Feed well to plump up the corm and you will have a flowering sized specimen in a few years.  Flowering sized corms often 'shatter' after the flowering, producing many smaller bulbs that will grow to flowering size again in a few years.  A. bulbifer will produce a mass of corms in between the leaf axils of the large palm like leaves which can be used to grow new plants.

This Years Test Results and Extra Tips

This year we conducted 200 test sowings amounting to 1/5th of our species overall and almost of 1/3rd of those species we test ourselves rather than just relying on the certification from the wholesaler/collector/grower.

As a result of these tests we have found that all of our cacti and succulent species continue to show excellent viability.  We also tested all Acacia, Cassia, Delonix and Erythrina species again with very good results.

Cacti and Succulents

We didn't use the ziploc bag method this time, instead we went for the covered tray.  Each batch was sown in a 7cm square pot of finely sieved (3mm) compost with a 25% addition of perlite to lighten up the mix.  The pots were watered before sowing and no chemical fungicides were used.  The seeds were all surface sown, then mist sprayed to settle in.  The pots then went in seed tray (15 per tray) and had a domed cover put over the top.  The whole thing then went on a heat mat giving a 10 Centigrade (18 F) lift over the ambient temperature this being in a greenhouse with a minimum temperature of 7.5 Deg C.  Placed on the 2nd shelf of the staging, underneath the main layer, this gave the perfect amount of bright filtered light (around 40% of what was available).  This mimics the ideal conditions where these seeds germinate in long grass or under shrubs.  Temperatures on the mat varied from 17.5C to 37.5 C depending on the temperature in the greenhouse.   1st seedlings showed after 3 days, last ones after 6 weeks (for cacti) and 10 weeks (succulents).  Percentages varied from 80% to 100% which, as ever, was species and age dependent.   Anything with less than 50% we planned to withdraw from sale, happily none fell into this category.

Acacias, Cassia, Delonix, Erythinas

These had a different treatment to the one we normally use.  Instead of boiling water we mechanically abraded every single seed used and then soaked them in tepid water until they swelled to at least twice the orginal size.  We then sowed them as per the cacti - the only difference being 50% were put in bags the other 50% in trays as per cacti.  Germination was even and good across the board and we saw 60 - 100% in every tested species.  Where we noted a difference was in after care, those in the bags fared less well than those in the covered trays once they were exposed to fresh air - conclusion the bag method produces a more even germination but a less robust seedling - we recommend that the covered method is used UNLESS you have time to check every day and get any seedlings out in to the fresh air immediately they show the first leaves.

Growing US Wildflowers From Seed

Growing Wildflowers from Seed (Perennials)

Pre Treatment

Not all seeds need any pre-treatment, those that do will be noted on the bottom of this care sheet with the recommended times.  If your seeds need pre-treating, then follow this guidance first, if not skip straight to the Sowing section.

The best form of pre-treatment is to sow the seeds in the autumn/winter in pots in a cold frame or other protected location (away from mice and birds) and to allow the winter cold to do the work for you.  Accepting that this is not always possible, the alternative method involves cold stratification (sometimes referred to as cold moist stratification).  To do this Place the seeds in a plastic bag or covered container.   Label the outside of the container with date and the seeds name.  Add an equal volume of sharp sand, moss or peat.  Add water to moisten and then mix contents.  The seeds should have some excess water the first day so they can absorb all they will.  After 24 hours check the seeds and add more sand, peat, or moss to absorb any excess moisture in the container.  The seeds should be moist not wet as they can drown in too much water.  Store the seed in the refrigerator (not the freezer) for the stated period in the table at the end of the sheet and then sow as below.

Sowing

The seed, whether treated as above or not, now needs to be surface sown either in a prepared outdoor nursery bed or in pots/trays of good seed raising compost.

Surface sow the seeds initially and then cover with a fine layer of the seeding mix, no more than the depth of the seeds themselves.  Buried too deeply the seeds will rot before they   grow.  The best germination temperatures are listed against each type in the list below and these refer to pot/tray sowings indoors in a heated propagator or frame.  Outdoor sowings can be done when the soil can be worked, but in the less controlled environment, the germination will be more erratic and considerably slower than indoor sowings.  That said, the subsequent plants go through less disturbance when planting out, so each method has its merits.

Germination should occur in most species in 4 – 8 weeks, although some take considerably longer – at all times patience is required and once they start to sprout they should be left until no more seedling emergence is observed for about a week or so.

Growing On

These instructions cover the perennial wildflowers, so once the plants are big enough, they will need to be either transplanted as they get crowded or thinned out (the first method is preferable where small batches of seed are involved as the second means throwing away the thinned out seedlings). In all cases it is best to wait till 2 sets of adult leaves are produced before up-rooting anything.

 
Plant out in their final locations in the autumn (fall) of the first year (for an early sowing) or the following spring for any later sowings.

Flowering can be expected from year 2, although some may take an extra year or so.

Genus	Stratification	Germination Temp
Allium	None	70 F
Amberboa	None	70 F
Aster	None	70 F
Balsamorhiza	1 Month at 70 F followed by 1 month Fridge.	50 F
Coreopsis	None	70 F
Dodecatheon	4 weeks	50 F
Echinacea	8 weeks	70 F
Gallardia	None	70 F
Gentiana	1 Month at 70 F followed by 1 month Fridge.	70 F - slow
Gilia	None	70 F - slow
Hibiscus	None	75 F
Helianthus	8 – 12 weeks	70 F – Autumn sowing is best
Ipomoea	None but soak for 24 hours in warm water.	70 F
Iris	1 Month at 70 F followed by 1 month Fridge.	50 F
Liatris	8 weeks	70 F
Lobelia	None	70 F
Lupinus	None but soak in hot water for 24 hours	70 F
Monarda	None	70 F
Oenothera	None	70 F
Papaver	None	70 F
Passiflora	8 – 12 weeks	70 F – Autumn sowing is best
Penstemon	None	45 F – slow (this is min temp)
Ratibida	None	70 F
Rosa	8 – 12 weeks	65 F – Autumn sowing is best
Rudbeckia	None	40 F – slow (this is min temp)
Sanguisorba	None	70 F
Schrankia	None	70 F
Scutellaria	8 weeks	70 F – Autumn sowing is best
Tradescantia	8 weeks	60 F

Remember only those mentioned above need pre-treatment, the rest can just be sown as per the section above – if sown in the open then they will germinate when the temperatures are sufficiently high.  If sown in trays then a minimum temperature of 65 F should be maintained for optimum germination.

Growing Annuals from Seed.

Annuals can be split into 2 groups.

Hardy annuals.

These can be directly sown as soon as the soil temperatures are above 45 F (6 Deg C).  Ensure the area is weed free as these will compete with your seedlings for space and light.  Thin out if the seedlings appear overcrowded.

If earlier flowers are required, sow in a seed tray of seedling compost and place in a temperature above 65 F (may require bottom heat to achieve this).  Prick out when large enough and space out to grow on.  Acclimatise to the outside temperatures about a week before the final planting time, which should be after the last expected frost in your area (even though they are hardy, you have grown them soft).

Half Hardy annuals.

These should be grown indoors at first like the second method for Hardy annuals.  The final acclimatisation should take place over a slightly longer period as these are not as tough as the Hardy annuals.

Biennials.

Although their life cycle takes place in 2 growing years, the length of time between seed and flower is roughly akin to those of annuals growing in one season.   These should be sown in the height of summer and in the early autumn, such that they germinate and grow somewhat in the first year, ready to flower in the early part of the second.  Follow the rules for Hardy annuals (apart from timing).